WO2006085886A1 - Lasers a solide employant une pompe a lumiere monochromatique incoherente - Google Patents

Lasers a solide employant une pompe a lumiere monochromatique incoherente Download PDF

Info

Publication number
WO2006085886A1
WO2006085886A1 PCT/US2005/007809 US2005007809W WO2006085886A1 WO 2006085886 A1 WO2006085886 A1 WO 2006085886A1 US 2005007809 W US2005007809 W US 2005007809W WO 2006085886 A1 WO2006085886 A1 WO 2006085886A1
Authority
WO
WIPO (PCT)
Prior art keywords
laser
light
excitation
excitation light
laser element
Prior art date
Application number
PCT/US2005/007809
Other languages
English (en)
Inventor
Ningyi Luo
Sheng-Bai Zhu
Shaoping Lu
Feng Zhou
Original Assignee
Pavilion Integration Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US11/052,725 external-priority patent/US7522651B2/en
Application filed by Pavilion Integration Corporation filed Critical Pavilion Integration Corporation
Publication of WO2006085886A1 publication Critical patent/WO2006085886A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/04—Arrangements for thermal management
    • H01S3/042—Arrangements for thermal management for solid state lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/0915—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light
    • H01S3/0933—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light of a semiconductor, e.g. light emitting diode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/025—Constructional details of solid state lasers, e.g. housings or mountings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/04—Arrangements for thermal management
    • H01S3/0407—Liquid cooling, e.g. by water
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/162—Solid materials characterised by an active (lasing) ion transition metal
    • H01S3/1625—Solid materials characterised by an active (lasing) ion transition metal titanium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/163—Solid materials characterised by a crystal matrix
    • H01S3/1631—Solid materials characterised by a crystal matrix aluminate
    • H01S3/1636—Al2O3 (Sapphire)

Definitions

  • This invention relates generally to the field of solid-state lasers, and more particularly, it relates to solid-state lasers pumped by incoherent monochromatic light sources such as light emitting diode(s) (LEDs).
  • LEDs light emitting diode
  • Solid-state lasers have found applications in all areas where high peak power or high continuous power are required. Examples include material processing (cutting, drilling, welding, marking, heat treating, etc), semiconductor fabrication (wafer cutting, IC trimming), graphic arts (printing, copying), biotechnology instrumentations (proteomics, DNA sequencing, flow cytometry), medical applications (diagnosis, therapy, micro-surgery), military applications (range finding, target designation), entertainment (laser TV, DVD), and scientific research, to mention a few.
  • solid-state lasers based on active ions doped in crystals or glasses are optically pumped.
  • One of the key components of a solid-state laser therefore is an efficient and low-cost light source to provide the optical pumping.
  • Such optical pumping of solid-state lasers requires the efficient conversion of electrical energy into optical radiation, and an efficient coupling between the generated high-radiation fluxes and the solid-state laser active (gain) medium. Efficient coupling requires a close match between the output spectrum of the pumping source and the characteristic absorption bands of the particular gain medium employed. To maximize the laser output and minimize thermal effects, precise spatial overlap and uniform absorption of pumped photons over the laser mode volume is important.
  • Flash lamps have been employed to pump solid-state lasers over the past years. All of these pumping sources have serious limitations and drawbacks, however.
  • flash lamps have been widely utilized for pumping solid-state lasers partly because of their high conversion efficiency.
  • the coupling efficiency is generally low.
  • Increasing the flashlamp's filling pressure could improve the conversion efficiency, however, this would require higher trigger voltage and the simmer current would be more difficult to establish and maintain.
  • the flashlamp's low coupling efficiency causes a large amount of heat to be generated during the pumping, which limits repetition rates of solid- state lasers pumped by flash lamps.
  • the excessive heating leads to undesirable thermal effects such as thermal birefringence, thermal lensing, and even thermal damage.
  • flash lamps typically exhibit short operating lifetimes. Consequently, their frequent replacement is necessary.
  • semiconductor diode lasers produce characteristically narrow emissions, which may be advantageously matched to the absorption peak of a laser's active medium, resulting in a high coupling efficiency.
  • semiconductor lasers are effectively low-peak-power devices and as such, are not applicable to high peak power pulsed mode operations and can be easily damaged by electrostatic discharge or current spikes.
  • the available output wavelengths of diode lasers are limited. Consequently, some wavelengths in the visible spectrum that have important applications -- such as pumping vibronic crystal lasers - are not available with diode lasers.
  • diode lasers have a relatively short lifetime of only 5,000 to 10,000 hours and their cost is relatively high.
  • incoherent monochromatic light sources such as the high-intensity Amplified Spontaneous Emissions (ASE) from rare-earth-doped fluoride, telluride and silica fibers, ASE from super-luminescent diodes, spontaneous emission from light emitting diodes (LEDs), and incoherent or partially coherent emission from vertical cavity surface emitting laser (VCSEL) arrays.
  • LEDs and VCSEL vertical cavity surface emitting laser
  • VCSELs are of particular interest, because their spectral bandwidths may suitably match the absorption spectrum of the lasing medium.
  • high power LEDs and VCSELs offer some particularly important wavelength ranges -- where conventional high power edge emitting laser diodes are unavailable. And unlike a flashlamp, which runs with an expensive high-voltage power supply of a large footprint, an LED can be driven easily with a low-voltage power supply.
  • Farmer and Kiang described the results of LED-pumped neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers.
  • Nd:YAG yttrium aluminum garnet
  • Farmer and Kiang described a solid-glass half-cylinder used for index matching and as a pumping cavity reflector for their Nd: YAG laser.
  • a LiNdP 4 Oi 2 laser pumped with an Al x Gai -x As electroluminescent diode was described by Saruwatara et al. in a paper published in Applied Physics Letters, Vol. 27, No. 12 on 15 December 1975. Therein, the authors disclosed that using an incoherent Al x Gai -x As light-emitting diode as a pump source, pulsed laser oscillation was observed in a LiNdP 4 Oi 2 crystal cooled to -35 0 C.
  • Additional Nd:YAG investigations were performed and described by Stone, Burrus, and Dentai in a paper appeared in Applied Physics Letters, Vol. 29, No. 1 , 1 July 1976. The authors achieved CW laser action using single-crystal Nd.YAG fibers end-pumped by a single high-radiance LED.
  • a laser structure consisting of an unguided uniform gain element and two mirrors forming a Fabry-Perot cavity was coupled to an LED pump.
  • incoherent light emanating from an incoherent monochromatic source such as an LED or VCSEL is coupled into a laser gain medium through the use of a diffusing pump chamber.
  • Our inventive pump chamber provides for multi-bounce reflections of unabsorbed pump light, resulting in uniform distribution of gain medium excitation, while at the same time, providing a convenient mechanical mounting for the source and associated driver electronics.
  • our inventive pump chamber provides for the efficient conduction of heat - away from the lasing components -- resulting in a laser capable of sustained, high-power, continuous (CW) or pulsed output - including those with extremely high repetition rates.
  • our inventive teachings result in solid state lasers exhibiting three basic characteristics, namely, 1 ) the efficient delivery of pump energy into a lasing media; 2) the efficient transfer of excited energy into stimulated emission with minimum loss from spontaneous emission or non-radiative quenching - a characteristic particularly important for laser materials having short upper state lifetimes; and 3) the novel integration of technologies such as high power LED arrays and solid-state laser materials in conjunction with the uniform absorption of pumping energies.
  • the resulting inventive structures are highly flexible, and therefore applicable to a large group of lasing media, operating at different modes that may be applied to a plethora of laser systems at wavelengths that have important applications not available to direct pumping technologies.
  • FIG 1A illustrates an embodiment of a basic solid-state laser according to the present invention
  • FIG 1 B is a 3-D illustration of the structure(s) depicted in FIG 1A;
  • FIG 1C is a functional block diagram of a solid-state laser according to the present invention.
  • FIG 2A shows a schematic, cross-sectional view of a pumping configuration according to the present invention
  • FIG 2B is a 3-D illustration of the structure(s) depicted in FIG 2A;
  • FIG 3A is a schematic, cross-sectional view of an alternative pumping configuration according to the present invention.
  • FIG 3B is a 3-D illustration of the structures depicted in FIG 3A;
  • FIG 4 is a graph comparing the absorption spectrum of
  • FIG 5A is a graph showing the radial distribution of excitation in the LED-pumped Alexandrite, Nd:Cr:GSGG, and Ti:sapphire lasing medium according to the present invention
  • FIG 5B is a graph showing LED pumping threshold as a function of output coupling for the LED-pumped Alexandrite laser both with, and without employing the full teachings of the present invention
  • FIG 5C is a graph showing the performance of Alexandrite laser pumped with red and blue LEDs, both with, and without employing the full teachings of the present invention
  • FIG 6 is a graph showing Nd:Cr:GSGG laser output as a function of blue LED pump power, both with and without employing the full teachings of the present invention
  • FIG 7A is a graph showing Ti:Sapphire laser output as a function of pulsed green LED pump energy, both with and without employing the full teachings of the present invention
  • FIG 7B is a graph showing the dependence of laser output energy on pulse repetition rate for Q-Switched TkSapphire laser pumped by a total of 125W optical power from green LED arrays according to the present invention.
  • FIG 8A is a schematic illustration of a solid-state laser constructed according to the teachings of the present invention.
  • FIG 8B is a schematic illustration of a solid-state laser having a coupling cavity and optional function blocks constructed according to the teachings of the present invention.
  • FIG 1A where an embodiment of a basic laser system 100, oftentimes called a “laser head”, is shown constructed according to the present invention. More specifically, an LED-pumped solid-state laser is illustrated therein.
  • laser gain medium 110 When operational, laser gain medium 110 is pumped by LED arrays 120 - disposed along a length of the medium 110.
  • the output emission spectra of the LED arrays 120 are selected to suitably match the absorption spectrum of the gain medium 110, which has a characteristic broadband absorption.
  • a resulting laser oscillation is generated in a laser or oscillation cavity formed between a highly reflective (HR) mirror 130 and an output coupler 140.
  • HR highly reflective
  • FIG 1B there is shown a 3-D illustration of a laser head section of the laser system depicted in FIG 1A with two laser cavity mirrors 130 and 140, disposed at each end of the laser, respectively.
  • the laser assembly is preferably covered by shell 150 and affixed to mounting plate 190.
  • One or more locating holes 191 are used for mounting the locating plate 190 and consequently the overall assembly, to another surface as required by the particular application.
  • the laser cavity mirrors 130, 140 are positioned external to the shell 150, vias or other passageways, disposed in end plates 160, permit optical communication between the gain medium 110 and cavity mirrors 130 and 140.
  • the resonant or laser cavity is defined by the optical path that exists between the cavity mirrors 130, 140, including the gain medium 110.
  • end plates 160 are located at each end of the laser assembly. Such end plates may preferably fix appropriate component(s), such as a laser rod and/or glass tube (or other elements), in an axial, or any other desired alignment.
  • An index matched coolant - such as water or other heat-conductive fluid with appropriate index of refraction is circulated though the system and as such may flow into inlet 170 and out from outlet 180 for cooling the laser medium (110 in FIG 1A) LED arrays (120 in FIG 1A), as well as other internal structures as necessary or desired.
  • FIG 1C is a functional block diagram of a solid-state laser constructed according to the present invention.
  • the LED pump source which is specifically labeled as 120 in FIG 1A, is energized by the electrical driver (not shown in FIG 1A). Part of the electrical energy is converted into incoherent and monochromatic radiation, which is further delivered into the laser gain medium, labeled as 110 in FIG 1A, through the coupling mechanism.
  • the driving energy is advantageously controlled through laser feedback.
  • our inventive teachings when combined with state-of-the-art computer controlled feedback, permits advantageously variable laser output, including pulsed output as well as sophisticated variable pulsed output all under computer or other automatic control.
  • FIG 2A there is shown in schematic form, a cross-sectional view of a solid-state laser 200 constructed according to our inventive principles.
  • a laser gain medium 210 is shown at the center or core of the inventive laser structure.
  • the laser gain medium 210 is situated within a tube 240 and axial aligned therein.
  • the entire assembly is further positioned within a housing 270.
  • inventive teachings are applicable to a variety of laser gain media, for example, Nd:Cr:GSGG, Alexandrite, TkSapphire, Nd:YVO4, Nd:GdVO4, Nd:YAG, Nd:KGW, CrSapphire (usually known as Ruby), CrLiSAF, CrYAG, CrForsterite, ErYLF, and Nd:glass, as well as other solid state materials that exhibit a spontaneous emission of photons as a result of a population inversion initiated by gain medium excitement with absorption-matching incoherent monochromatic sources such as arrays of LEDs or VCSELs.
  • active ion doping levels may vary vastly to meet desired operating conditions and/or to desirably modify the mode- pump overlap.
  • the diagram depicts an exemplary cross-sectional view of our inventive laser structure 200. Consequently, the laser gain medium 210 is rod, or cylindrically shaped, and is shown as the innermost component of laser structure 200. It is understood that, the precise cross- sectional shape of the laser gain medium may vary considerably, with circular, elliptical, rectangular, hexagonal, octagonal and polygonal shapes all being possible with our invention. Additionally, and depending on the required laser output, the precise length of the laser gain medium may vary considerably as well.
  • a gap 250 which, in a preferred embodiment, contains a circulating, index matched coolant such as water (distilled or deionized) or salt solutions exhibiting an appropriate index of refraction to index match laser gain medium rod 210 and diffusion chamber 240 that is constructed from a glass (or other suitable material transparent to the pumping light) tube.
  • the gap 250 is a space or other void formed between the outer surface of the laser gain medium 210 and the inner surface of the tube 240.
  • the circulating, indexed matched coolant liquid removes heat generated during laser operation thereby maintaining laser thermal stability.
  • it is transparent to the pump light produced by an LED or other pump source employed.
  • each individual LED array 230 includes a number of individual LEDs (not specifically shown), typically arranged and packaged one by one. Each individual LED emits its respective pump light that illuminates and pumps the laser gain medium 210.
  • the specific number of the LEDs in each array and their particular operational and emission characteristics may be selected to enhance or otherwise optimize the performance of the laser.
  • the total pumping energy generated by the LED arrays 230 must be sufficient to induce lasing operation while not being too high to avoid efficiency reduction and, probably, thermal damage.
  • Each of the LED arrays 230 is mounted on fixtures 260 which may also serve as LED driver mounting base and heat sinks, carrying any excessive heat away from LED arrays 230 as appropriate.
  • the outermost housing is preferably a metal shell 270, or other material that provides suitable physical protection of the laser system and heat dissipation characteristics. Accordingly, heat-conductive plastics or ceramics are suitable materials for incorporation into our inventive laser.
  • the outer surface 242 of the tube 240 is coated to be highly reflective, except for generally slot-shape areas providing transmitting windows 241 for the LED pumping light to enter into the tube 240 and subsequently into the gain medium 210.
  • 241 slots are anti-reflective (AR) coated to minimize reflection loss at the pump wavelength.
  • the outer surface 242 of the tube 240 may be etched to be uneven and coated with dielectric HR film or metallic film to provide diffusive reflection of pump light.
  • an additional gap or chamber 220 is formed between the outer surface of the tube 240, and an inner surface of the housing or shell 270.
  • This gap 220 can be filled with highly diffusive reflecting materials such as Spectralon, BeO, MgO, BaSO4, or ceramics for diffuse reflection, and the outer surface 242 of the tube 240 can then be all AR coated.
  • Such a configuration results in this outer gap 220 effectively serving as a "diffusion" chamber, which further enhances the coupling efficiency of pump light, emitted from the arrays of LEDs 230, and the gain medium 210.
  • the LED arrays 230 When operational and energized, the LED arrays 230 emit light at a wavelength characteristic of the particular LED.
  • this operation may be made continuous, pulsed, or some desirable variation thereof.
  • the light emitted from the LED arrays 230 passes through respective AR transmitting windows 241 , the tube 240, the index matched coolant (water or other appropriate liquid) 250, and into the laser gain medium 210.
  • the index matched coolant water or other appropriate liquid
  • most of the light emitted from the LED arrays 230 strikes and is subsequently absorbed by the gain medium rod 210. Nevertheless, a portion of that emitted light is either not absorbed by the gain medium rod or fails to strike it altogether.
  • the rod 210 or does not initially strike the rod 210, is reflected back internally towards the gain medium rod through the effect(s) (either combined or individually) of the reflective outer surface 242 of the tube 240, diffusive material (not specifically shown) situated in gap 220, or a highly reflective inner surface of housing 270.
  • FIG 2B provides a perspective, 3-D view of the inventive structure of FIG 2A.
  • laser assembly 300 includes a gain medium 310, positioned within and in axial alignment with, a tube 340, which is transparent to the pumping light, and a number of LED arrays 330, positioned around the outer perimeter of the tube 340 and preferably disposed uniformly around the inner surface of shell 320.
  • the number of LED arrays is preferably an odd number, i.e., 3, 5, 7, etc. and the length of each array is positioned such that it is parallel to the length of the gain medium 310.
  • FIG 3B provides a perspective, 3D-view of the structure depicted in FIG 3A for additional, simultaneous reference.
  • the outer surface 341 of tube 340 is coated with a material that is antireflective (AR) at the pumping wavelength. Consequently, light emitted from the LED arrays 330 is not significantly reflected by this outer surface of the tube 340.
  • the coating may beneficially contain a special layer or certain materials exhibiting strong absorption at the lasing wavelength to suppress unwanted ASE and, therefore, to eliminate parasitic laser transitions.
  • the tube 340 is constructed from common borosilicate glass material, i.e., Pyrex, or other dimensionally stable, chemically resistive, and optically transparent materials sufficient to permit the satisfactory optical pump of the laser gain medium 310.
  • gap 370 Concentrically overlying the tube 340 is gap 370 that formed in a void existing between the tube 340 and the inner surface of shell 320.
  • the tube 340 is shown as being cylindrical in shape, and within its hollow core is positioned laser gain medium rod 310, which runs lengthwise, in axial alignment with the tube 340. Bathing the rod, and contained within the tube 340, is an index-matched coolant, which is preferably circulated to remove heat from the operating laser assembly. [0063] Continuing with our discussion of the laser structure 300 depicted in FIG 3A, each of the LED arrays 330 is mounted on fixtures 360 which may also serve as heat sinks.
  • the inner surface 321 of shell 320 is preferably roughened and coated with HR metallic film or dielectric film or polished metal surface to provide effective diffused reflection.
  • one or more of the individual diodes contained in LED arrays 330 are energized such that they emit one or more characteristic pump lights. It is important to note that the operation of the LEDs may be continuous or selectively turned on or off such that they operate intermittently and thereby "pulse" the laser.
  • individual arrays or LEDs may be selectively operated - preferably under computer or other automatic control - to produce a desired output.
  • the LED arrays are disposed lengthwise (as in FIG 3B) along the laser gain medium 310, the LEDs may be selectively operated along the length as well as the perimeter to realize any beneficial operational performance that may result from such operation.
  • the light emitted from the LEDs passes through the tube 340 and the gap 350 containing index-matched coolant. While much of the light does strike the laser gain medium 310, that portion of the light which does not, or which passes through the gain medium 310, will eventually strike the highly reflective (HR) inner surface 321 of outer chamber (shell) 320 where it will be reflected back towards the laser gain medium 310. This process may be repeated a number of times, thereby enhancing the efficiency of the inventive structure while promoting a uniform gain distribution within the gain medium.
  • the pump or diffusion chamber may be defined by those regions of the structure between the inner surface of the outer shell 321 and the gain medium 310.
  • the outer surface of the laser gain medium rod 310 may be ground to give a surface roughness of 20 to 100 micro inches RMS.
  • our inventive structures may be quite compact -- , the overall dimensions of the structure depicted in FIG 3A may be on the order of 30mm x 20mm, or smaller.
  • inventive concepts may be enhanced through the use of a pair of lenses or a single lens, located at an exit aperture of the LED arrays (230 in FIG 2A or 330 in FIG 3A) to further guide and confine the pump light towards the laser gain medium 210.
  • our inventive concepts may be further enhanced by the use of LED arrays with a photonic crystal layer or polymer domes or coupling lenses for efficiency improvement.
  • FIG 3B provides a perspective, 3D view of the inventive structures depicted in planar view in FIG 3A.
  • incoherent monochromatic pump light sources such as LEDs
  • their couplings As can be appreciated, recent advances in visible wavelength high power LEDs enable efficient excitation of solid-state lasers, in particular, near IR tunable lasers and femtosecond short pulse lasers based on vibronic laser materials.
  • the incoherent emission from such high power LEDs typically has a bandwidth of -40 nm and can be packaged to radiate within a limited divergence angle of ⁇ 30°.
  • the reader is referred to Table I, and in particular three representative materials, namely, Alexandrite, Nd:Cr:GSGG, and Ti.Sapphire.
  • Alexandrite (BeAbO 4 ICr 3+ ) can produce tunable laser emission at 700 nm - 818 nm. Due to the relatively long spontaneous lifetime of its upper state, i.e., 260 ⁇ s at 25 0 C, an Alexandrite laser can be operated at
  • FWHM of approximately 170 nm which is a good match for the blue light (420 nm, FWHM « 30 nm) and orange light (590 nm, FWHM « 30 nm) emanating from GalnN/GaN or InGaAsP/GaAsP LEDs.
  • Nd.Cr.GSGG is an important source of 1061 nm laser, both CW and pulsed.
  • Cr 3+ is a sensitizer, utilized for improving efficiency through the mechanism of transferring excitation. Due to the broad absorption bands of chromium, the material can efficiently absorb light throughout the whole visible region of the spectrum, although it is particularly sensitive to blue light such as the emission from GalnN/GaN LED.
  • the TkSapphire (TKAI 2 O 3 ) laser is probably the most widely used tunable solid-state laser.
  • TKAI 2 O 3 the TkSapphire
  • This material exhibits a broad absorption band, located in the blue-green region of the visible spectrum with a peak around 490 to 510 nm and FWHM « 50 nm.
  • diode lasers there are currently no suitable diode lasers to match this range.
  • due to its very short fluorescence lifetime - around 3.2 ⁇ s - direct flashlamp pumping is difficult.
  • Table I Major solid-state laser materials to be directly pumped by LED or
  • Configuration A represents a full implementation of the present invention which is a simplified structure of that depicted in FIG 2A or FIG 3A. More specifically, a laser gain medium (rod) is concentrically placed at the center of a cylindrically shaped diffusion chamber. Three or five of LED bars are evenly installed on the chamber wall.
  • Configuration B is identical to that Configuration A, but without the diffusion chamber. Therefore, it represents a partial implementation of the present invention. A comparison of the results from these two configurations shows the advantage of employing the entire, inventive coupling structure.
  • the first simulation evaluates the pump uniformity of Configuration A.
  • the diameter of the laser gain medium is assumed to be 2 mm.
  • Radial distributions of the excitation in three different laser materials, namely Alexandrite, Nd:Cr:GSGG, and Ti:Sapphire are calculated.
  • FIG 5A displays the results.
  • the resultant illumination at the Alexandrite rod center is about 6% higher than that at the rod edge.
  • the illumination at the center is 8% higher than that at the edge, while for TkSapphire, it is 5%.
  • FIG 5B Plotted in FIG 5B are curves of the pumping power threshold vs. the laser cavity output coupler transmission for LED pumped Alexandrite lasers. These curves clearly show that with a full implementation of the present invention, the required LED pump power to reach laser threshold may be dramatically reduced. In particular, one may conclude that our inventive structure(s) make compact, LED-pumped lasers realistic.
  • Configuration B a partial implementation of our inventive teachings of present invention is represented by Configuration B.
  • the threshold of light from LED sources 3 mm away from the gain medium rod center, would be approximately 160 W for a laser system with an Alexandrite rod of 2 mm in diameter and the output coupler transmission of 1 .5%. This requires at least 160 LEDs, each with 1 W light output. Provided that the LED conversion efficiency is
  • the total surface area that can be used to mount the LEDs is less than 470 mm 2 , or less than 3 mm 2 per
  • LED While increasing the distance between the LED sources and the rod center provides more mounting area, it reduces the light-medium coupling efficiency and, consequently, requires more LEDs. For example, increasing the distance from 3 mm to 5 mm would raise the threshold by 65%, which increases the minimally required number of LEDs from 160 to 263.
  • conventional approaches are simply not practical, both physically and economically, for LED-pumped solid-state laser systems.
  • a suitable population inversion can be generated in the same laser system incorporating our inventive structure and only three LED bars or arrays, each having 22 individual LEDs providing 1 W light output each.
  • Such a configuration consumes only 330 W in electrical power and the heat generated during operation can be easily removed. This threshold can be further reduced when the LEDs are operated in pulsed modes.
  • certain laser materials having doping atoms located within a crystal have a short lifetime for the upper level, resulting in a very high pumping threshold.
  • the upper laser level of TkSapphire material at the room temperature is only 3 ⁇ s, and will be even shorter as the temperature increases.
  • directly pumped Tksapphire lasers can be constructed.
  • 1 .3 mJ/pulse output can be obtained from a ThSapphire laser having a gain medium diameter of 2 mm, a coupler transmission of 2.4%, and pumped by LED arrays operating at pulsed mode with 15 mJ energy per pulse, 3 ⁇ s pulse width, and 25 kHz repetition rate. Absent our inventive teachings, the slope efficiency of such a laser system would be much lower and therefore impractical at best.
  • FIG 7B The dependence of Tksapphire laser output energy on pulse repetition rate is depicted in FIG 7B, wherein additional advantages resulting from the pulsed operation of laser constructed according to our inventive teachings, may be realized.
  • lasers constructed according to our inventive teachings may be operated at various high repetition rates.
  • the three curves depicted in that FIG 7B respectively represent three different maximum peak powers, all with a LED pump with pulse width of 3 ⁇ s.
  • the highest repetition rate without reduction of the output energy per pulse would be 66.7 kHz.
  • the LED arrays are allowed to operate the pumping power at ten times the average power, or equivalent ⁇ 1250 W peak power, the laser output energy reaches 0.14 mJ/pulse for a repetition rate of up to 33.3 kHz.
  • the maximum peak power is assumed to be 1 %.
  • Tksapphire lasers can be constructed and operated at high repetition rates -producing usable energy per output pulse.
  • Ti:Sapphire lasers can be used for many applications.
  • the incoherent, monochromatic light such as the one emitting from LED arrays must spectrally match the absorption of the gain medium, which can be quantitatively defined as the integral of the product of the two spectra over the wavelength; and 2) in order to make compact and robust lasers, the LED arrays must be able to produce high power density, preferably, 1 W/cm 2 or higher, depending on the specific lasing material and operation mode. In many applications, compact lasers with the ability to operate over a wide temperature ranges are required thereby increasing the importance of our inventive teachings.
  • the preferable number of LED bars is three or five.
  • FIG 8A a solid-state laser system 800 that is a generalization of the inventive structure(s) shown previously, and in particular those of FIG 1A.
  • the laser system 800 includes a laser gain medium 810, LED pump sources 820, an HR mirror 830, an output coupler 840, together with optional components 850, 860, and 870.
  • Component 860 which can be a prism or a birefringent filter (BRF), is inserted between the laser medium 810 and the output coupler 840 to provide wavelength selection of tunable laser systems.
  • An etalon may be used in conjunction with the prism or BRF 860 to further reduce the laser linewidth to a single longitudinal mode (SLM).
  • SLM single longitudinal mode
  • such lasers may operate either in CW or pulsed mode, depending on the LED pumping condition and the laser operation mode.
  • a specially coated dielectric chirped mirror an LED pumped broadband laser with flat-top output in the spectral domain may be realized.
  • such laser systems are highly desirable for certain applications including RGB color projection displays with minimum speckle effects, or high power laser amplifier systems with minimum nonlinear effects.
  • component 850 which is inserted between the laser medium 810 and the HR mirror 830, still other useful variations of our inventive teachings can be constructed.
  • component 850 may be a Q-switch and both AO-switching and EO-switching may be applied.
  • the LED can operate in either CW or pulsed mode. In the latter case, the timing must be synchronized with the Q-switching.
  • component 850 is an Acusto- Optical Modulator (AOM), or passive mode-locker, such as a quantum-well based saturable absorber
  • AOM Acusto- Optical Modulator
  • passive mode-locker such as a quantum-well based saturable absorber
  • the laser operates on active or passive mode locking.
  • component 850 is a combination of an acousto-optical modulator and a passive mode-locker, such as a quantum-well based saturable absorber
  • mode locking with Q- switching can be realized.
  • picosecond and femtosecond pulses can be generated.
  • component 870 can be a seeding laser and can be embodied differently for reduction of laser build-up time, TEMOO output beam quality control, control of lasing wavelength, control of laser temporal pulse shape, to mention a few.
  • component 870 is a seeding diode laser having a single frequency used in conjunction with beam-shaping optics. The resulting structure(s) enable our inventive LED pumped lasers to operate in SLM condition.
  • component 870 includes a seeding diode laser producing ultrashort (picosecond or femtosecond) pulses, in conjunction with a beam shaping system, to enable high peak power per pulse from an LED directly pumped laser, especially the pulsed LED pumped Ti:sapphire laser.
  • component 870 is a seeder producing nanosecond short pulse in pulsed operation and is used to seed a short cavity solid state laser, such as TkSipphire, which is synchronously pumped by short pulse LED arrays. With this configuration, laser output of good beam quality with large beam size can be obtained in an ordinary Fabry-Perot cavity.
  • component 870 includes a seeding diode laser with a broad spectrum (1 nm or wider), in conjunction with a set of beam-shaping lenses. This embodiment enables a broadband laser output with high brightness and low coherence, which is particularly useful for applications such as laser projection. As should be apparent to the person skilled in the art, there are a number of other alternative embodiments of component 870.
  • the component 880 may be a dichroic mirror or a thin film polarizer (TFP) that forms a coupling cavity or so-called composite cavity for intracavity nonlinear process.
  • Component 890 may be a nonlinear optical device such as a harmonic generator or a parametric oscillator.
  • based lasers can be extended to 350-500 nm (second harmonic) and 235-335 nm (third harmonic).
  • a BBO, LBO, KTP, BiBO, KBBF, or a CLBO nonlinear crystal (NLC), which generates the harmonic wavelengths can be positioned inside (or outside) of the laser cavity 800.
  • NLC CLBO nonlinear crystal
  • component 880 can be a dichroic mirror or TFP, which sits between the primary cavity and the composite cavity and allows the passage of the primary wavelength only. Any primary light, which is not converted to its second harmonic, will return into the primary cavity for normal laser oscillation.
  • the second harmonic thus generated on the other hand, resonantly oscillates in a coupling cavity or so-called composite cavity formed by component 880 while can never enter the primary cavity to avoid energy loss. In this way, the frequency doubling is optimized.
  • the component 880 can be a polarizer and component 890 can be an acoustic modulator or a wave plate together with a Pockels Cell for cavity rapid dumping of optical energy.
  • This configuration can also be used to construct a regenerative amplifier. Cavity dumping or regenerative amplifier is commonly used to generate intense short laser pulses.
  • 3A can be used to construct LED-pumped solid-state laser amplifiers. Again, various laser gain materials can be selected and the number and length of LED arrays can vary to meet the required operation conditions.
  • inventive structure can be obtained by combining our inventive principles with other techniques, e.g., highly reflecting compound parabolic concentrator (CPC), concentrator with two overlapped parabolic portions, and multiple CPCs.
  • CPC compound parabolic concentrator
  • the CPC surface can be constructed by metal or Pyrex glass coated with highly reflecting metal film or dielectric HR thin film or highly diffuse reflecting materials such as
  • Spectralon, BeO, MgO, or BaSO4, or a highly diffuse reflecting ceramics exhibits advantageous manufacture/assembly characteristics and is an ideal candidate as a high power pumping source.
  • a host lattice material include gadolinium gallium garnet (GGG), gadolinium scandium gallium garnet (GSGG), LiCAF, LiSAF, sapphire, KGW, ruby and alexandrite.
  • Suitable single or multiple dopants for this lasing medium include Ti, Cr, Pr, Nd, Ho, Er, Tm, and Yb.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Lasers (AREA)

Abstract

La présente invention concerne des lasers à solide pompés par la lumière monochromatique incohérente provenant de sources telles que des rangées de DEL et intégrant des techniques telles que des rangées de DEL puissantes et des matériaux laser à solide associés à une absorption efficace et uniforme des énergies de pompage par une chambre de pompe de diffusion. Les lasers résultant sont compacts, résistants, peu coûteux et capables de fournir un rendement à grande puissance pour des applications pratiques. Ils sont opérationnels sur de vastes plages de températures et de performances, en mode en continu ou à impulsion, même avec des largeurs d’impulsion extrêmement courtes et/ou à des vitesses de répétition extrêmement élevées. La structure ou les structures de l’invention est ou sont très flexible(s) et peut ou peuvent être appliquée(s) à un vaste groupe de matériaux actifs, y compris à ceux ayant des durées de vie à l’état maximum très brèves. Elle(s) peut ou peuvent être avantageusement appliquée(s) à une pléthore de systèmes laser à des longueurs d’ondes qui ont des applications importantes et qui ne sont pas disponibles avec d’autres techniques de pompage direct.
PCT/US2005/007809 2005-02-07 2005-03-11 Lasers a solide employant une pompe a lumiere monochromatique incoherente WO2006085886A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US11/052,725 US7522651B2 (en) 2004-03-10 2005-02-07 Solid-state lasers employing incoherent monochromatic pump
US11/052,725 2005-02-07

Publications (1)

Publication Number Publication Date
WO2006085886A1 true WO2006085886A1 (fr) 2006-08-17

Family

ID=36793346

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2005/007809 WO2006085886A1 (fr) 2005-02-07 2005-03-11 Lasers a solide employant une pompe a lumiere monochromatique incoherente

Country Status (1)

Country Link
WO (1) WO2006085886A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT503819B1 (de) * 2006-08-24 2008-01-15 Ctr Carinthian Tech Res Ag Verfahren und anordnung zur regelung der laser-pulsenergie
WO2008046257A1 (fr) * 2006-10-13 2008-04-24 Shenzhen Han's Laser Technology Co., Limited Cavite de pompage incidente concentrique

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3821663A (en) * 1973-01-15 1974-06-28 Motorola Inc Integral reflecting cavity semiconductor pumped laser
US6282217B1 (en) * 1998-09-04 2001-08-28 Kabushiki Kaisha Toshiba Solid-state laser device
EP1315257A1 (fr) * 2000-07-13 2003-05-28 Artur Afanasievich Mak Module de laser a plaquette a corps solide avec pompage optique

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3821663A (en) * 1973-01-15 1974-06-28 Motorola Inc Integral reflecting cavity semiconductor pumped laser
US6282217B1 (en) * 1998-09-04 2001-08-28 Kabushiki Kaisha Toshiba Solid-state laser device
EP1315257A1 (fr) * 2000-07-13 2003-05-28 Artur Afanasievich Mak Module de laser a plaquette a corps solide avec pompage optique

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT503819B1 (de) * 2006-08-24 2008-01-15 Ctr Carinthian Tech Res Ag Verfahren und anordnung zur regelung der laser-pulsenergie
WO2008046257A1 (fr) * 2006-10-13 2008-04-24 Shenzhen Han's Laser Technology Co., Limited Cavite de pompage incidente concentrique
CN101162827B (zh) * 2006-10-13 2010-09-08 深圳市大族激光科技股份有限公司 一种对心注入式泵浦腔

Similar Documents

Publication Publication Date Title
US7522651B2 (en) Solid-state lasers employing incoherent monochromatic pump
US7430231B2 (en) Vertical cavity surface emitting laser (VCSEL) arrays pumped solid-state lasers
US7633979B2 (en) Method and apparatus for producing UV laser from all-solid-state system
US5351251A (en) Laser apparatus
US9160131B2 (en) Transition-metal-doped thin-disk laser
US6009114A (en) Method and apparatus for pumping of transition metal ion containing solid state lasers using diode laser sources
US5182759A (en) Apparatus and method for pumping of a weakly absorbing lasant material
US4756003A (en) Laser diode pumped solid state laser
JP2000058951A (ja) Ｎｄ―ＹＡＧレ―ザ
EP1618634B1 (fr) Systeme laser a milieu amplificateur solide sans danger pour les yeux
US4167712A (en) Praseodymium blue-green laser system
US5841805A (en) Three-level laser system
US4956843A (en) Simultaneous generation of laser radiation at two different frequencies
US4490822A (en) Cr-Doped yttrium gallium garnet laser
Rustad et al. Low threshold laser-diode side-pumped Tm: YAG and Tm: Ho: YAG lasers
WO2006085886A1 (fr) Lasers a solide employant une pompe a lumiere monochromatique incoherente
Xiong et al. High power VCSEL array pumped Q-switched Nd: YAG lasers
US6859480B2 (en) Tm:YAG laser
CN1328367A (zh) 一种多波长晶体激光器
MOHAN LASERS: Medical and Cosmetic Photonics
Titterton et al. Progress with a flashlamp-pumped titanium sapphire laser
Titterton Liquid lasers
Eichler et al. Solid-State Lasers
Koechner et al. Laser oscillator
Pratesi Diode-Pumped Miniature Solid State Lasers

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application
NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 05725147

Country of ref document: EP

Kind code of ref document: A1