CN111142178B - Microstructure low-oscillation back coated chirped mirror and preparation method thereof - Google Patents
Microstructure low-oscillation back coated chirped mirror and preparation method thereof Download PDFInfo
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- CN111142178B CN111142178B CN202010064010.7A CN202010064010A CN111142178B CN 111142178 B CN111142178 B CN 111142178B CN 202010064010 A CN202010064010 A CN 202010064010A CN 111142178 B CN111142178 B CN 111142178B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/08—Mirrors
- G02B5/0816—Multilayer mirrors, i.e. having two or more reflecting layers
- G02B5/0825—Multilayer mirrors, i.e. having two or more reflecting layers the reflecting layers comprising dielectric materials only
- G02B5/0833—Multilayer mirrors, i.e. having two or more reflecting layers the reflecting layers comprising dielectric materials only comprising inorganic materials only
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
- G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
- G02B1/11—Anti-reflection coatings
- G02B1/118—Anti-reflection coatings having sub-optical wavelength surface structures designed to provide an enhanced transmittance, e.g. moth-eye structures
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/20—Exposure; Apparatus therefor
- G03F7/2051—Exposure without an original mask, e.g. using a programmed deflection of a point source, by scanning, by drawing with a light beam, using an addressed light or corpuscular source
- G03F7/2053—Exposure without an original mask, e.g. using a programmed deflection of a point source, by scanning, by drawing with a light beam, using an addressed light or corpuscular source using a laser
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Abstract
The invention provides a microstructure low-oscillation backside coated chirped mirror which has a structure of A/M/G/C, wherein A represents an air layer, M represents an anti-reflection microstructure, G represents a substrate, and C represents a chirped film system. The refractive index of the substrate material is close to that of a low refractive index material in the chirped film system, and the chirped medium film system structure is formed by alternately depositing high and low refractive index materials. The invention etches an anti-reflection microstructure on the surface of the substrate to reduce the optical loss, and combines the impedance matching principle to plate the chirped film system on the back of the substrate, and utilizes the property that the refractive index of the substrate is close to that of the low-refractive-index material in the chirped film system to reduce the group delay dispersion oscillation. Therefore, the low-oscillation dispersion mirror for pulse compression and broadening in an ultrafast laser system is designed.
Description
Technical Field
The invention belongs to the field of ultrafast laser films, particularly relates to a low-oscillation dispersion mirror in a femtosecond pulse laser system, and discloses a high-reflection mirror for pulse compression and broadening in the femtosecond laser system.
Background
In the field of ultrafast laser, the quality of a dispersion compensation mode directly influences the generation and stable output of ultrafast laser pulses, and the invention and the use of a dispersion mirror have milestone significance for the ultrafast laser. Compared with the traditional dispersion compensation element prism and grating pair, the dispersion mirror has the advantages of more accurate dispersion compensation mechanism, compact structure and the like, different delays are given to light with different wavelengths by the dispersion mirror, namely the penetration depths of the light with different wavelengths in the dispersion mirror are different, so that different lights have different delays, the purpose of dispersion compensation is achieved, and high-order dispersion and nonlinear effects cannot be introduced while the dispersion mirror provides accurate dispersion compensation.
The dispersion mirror is mainly divided into a high dispersion mirror, a broadband chirped mirror and a low dispersion mirror. The low dispersion mirror is the most commonly used optical element in laser systems, and by providing near-zero group delay dispersion within the reflection bandwidth, it is ensured that only the transmission direction of the laser pulse is changed when passing through the low dispersion mirror, and no additional dispersion is introduced. The high dispersion mirror is a mirror that gives a sufficiently large amount of dispersion compensation while maintaining a high reflection output in a narrow bandwidth range. The broadband chirped mirror is an optical element essential for compensating dispersion in a cavity of an ultrafast laser system, and an important standard for evaluating the performance of the broadband chirped mirror is the reflection bandwidth and the dispersion oscillation size of the broadband chirped mirror, but the reflection bandwidth and the dispersion oscillation are a pair of contradictory variables, and the dispersion oscillation is certainly aggravated due to the increase of the reflection bandwidth. This is mainly caused by impedance mismatch between the chirped film system and the external air layer, and the optical pulse will form interference between the partially reflected light on the surface of the film and the highly reflected light on the bottom of the film, and finally the dispersion curve will oscillate, and the pulse splitting will be caused by too large dispersion oscillation.
In order to eliminate the dispersion oscillation of the broadband chirped mirror, various design ideas are proposed internationally, and mainly comprise: brewster angle chirped mirrors, double chirped mirrors, inclined surface chirped mirrors, back coated chirped mirrors, etc. At present, a common method is a chirped mirror pair, which shifts the central wavelength or the incident angle to make the dispersion oscillation of two mirrors have a half-period shift, so that the oscillation ripples of the two mirrors are cancelled positively and negatively, and the dispersion curve is relatively smooth. However, the design of chirped mirrors in pairs is a not insignificant challenge from both design and manufacturing considerations.
Disclosure of Invention
The invention provides a microstructure low-oscillation back-coated chirped mirror, which is characterized in that a periodic anti-reflection array structure is etched on the surface of a substrate, the optical loss is reduced, a chirped film system is coated on the back of the substrate by combining an impedance matching principle, and the group delay dispersion oscillation is reduced by utilizing the characteristic that the refractive index of the substrate is close to that of a low-refractive-index material in the chirped film system.
The technical scheme of the invention is as follows:
a microstructure low-oscillation backside-coated chirped mirror has a structure of A/M/G/C, wherein A represents an air layer, M represents an anti-reflection microstructure, G represents a substrate, and C represents a chirped film system. The anti-reflection microstructure is a periodic array structure, the refractive index of the substrate material is close to that of a low-refractive-index material in the chirped film system, and the chirped medium film system structure is formed by alternately depositing high-refractive-index materials and low-refractive-index materials.
The expression of the chirped mirror structure is A/M/G/(HxL) ^ M (xHL) ^ n (HL) ^ k/, wherein A represents an air layer, M represents an antireflection microstructure, G represents a substrate, H is a high-refractive-index material with the optical thickness of lambda/4, L is a low-refractive-index material with the optical thickness of lambda/4, n and M are the number of cycles of a cavity, x is the thickness of the cavity, and k is the number of cycles of a high-reflective film.
The selection range of the number k of the periods of the high-reflectivity film layer is 7-20, the thickness x of the cavity is 1.2-3, and the number m and n of the periods of the cavity are 5-18.
The material of the substrate layer is quartz glass, K9(BK7) or CaF2And the thickness is less than 0.5 mm.
The medium thin film material with high refractive index in the chirped film system is TiO2，Nb2O5，Ta2O5，HfO2，ZrO2Fluoride, sulfide, or Si.
The medium thin film material with low refractive index in the chirp film system is SiO2。
Each unit of the periodic array structure is in a shape of a cuboid, a cylinder, a cone, a truncated cone, a pyramid or a parabolic cone.
A method for preparing the microstructure low-oscillation back-coated chirped mirror is characterized by comprising the following steps: the method comprises the following steps:
step 1) spin-coating photoresist on a substrate, and preparing a required mask pattern by adopting a laser holographic interference technology.
And 2) transferring the mask prepared in the step 1 to a substrate by adopting a reactive ion beam etching technology to prepare a periodic array structure.
And 3) depositing a chirped film system on the back surface of the substrate with the periodic array structure prepared in the step 2.
The beneficial technical effects of the invention are as follows:
the invention etches an anti-reflection microstructure on the surface of the substrate, reduces the optical loss, plates a chirped film system on the back of the substrate by combining the impedance matching principle, and designs the low-loss and low-oscillation chirped mirror in a broadband range by utilizing the property that the refractive index of the substrate is close to that of a low-refractive-index material in the chirped film system.
Drawings
FIG. 1 is a schematic diagram of a microstructure low-oscillation backside coated chirped mirror according to the present invention.
The figure is sequentially provided with a chirp film system, a substrate, an anti-reflection microstructure and an air layer from bottom to top.
FIG. 2 is a schematic diagram of an anti-reflective periodic array structure unit.
FIG. 3 shows the transmittance of a substrate with an anti-reflection microstructure etched on the surface.
FIG. 4 is a back-chirped film group delay dispersion curve.
Detailed Description
The following detailed description of specific embodiments of the invention refers to the accompanying drawings.
As shown in FIG. 1, a microstructure low-oscillation backside-coated chirped mirror has a structure of A/M/G/C, wherein A represents an air layer, M represents an anti-reflection microstructure, G represents a substrate, and C represents a chirped film system. The method is characterized in that: the anti-reflection microstructure is a periodic array structure, the refractive index of the substrate material is close to that of a low-refractive-index material in the chirped film system, and the chirped medium film system structure is formed by alternately depositing high-refractive-index materials and low-refractive-index materials.
Example 1 index: 200fs2@ 780-.
In terms of substrate material, quartz glass is mixed with conventional low refractive index material SiO2Has very close refractive indexes, so quartz glass JGS1 is selected as the substrate material in the present example. Furthermore, since the incident light passes through the base material, the dispersion of the base material cannot be ignored, and the thickness of the base material is as thin as possible, in this example the thickness of the base JGS1 is 0.5mm (800nm center wavelength, 0.5mm quartz base incorporates +24 fs)2Positive dispersion).
In terms of periodic array structure selection, the present example selects a parabolic cone as shown in figure 2 (cross-sectional view),
the material of the chirp film layer is selected from a high-refractive-index material Nb2O5The low refractive index material is SiO2The refractive index parameters of the high and low refractive index materials are determined by the following cauchy formula:
wherein A is0，A1，A2The Cauchy dispersion coefficient is different depending on different media, λ is the wavelength, and n (λ) is the refractive index corresponding to the wavelength λ. The parameters of this example are shown in Table 1.
TABLE 1
And selecting a proper initial structure according to the requirements of the low-oscillation dispersion mirror. The initial structure of this example is A/M/G/(H1.5L) ^10(1.5HL) ^10(HL) ^13, where A represents an air layer, M represents an anti-reflection microstructure, G represents a substrate, H is a high refractive index material with an optical thickness of lambda/4, and L is a low refractive index material with an optical thickness of lambda/4. Setting the optimization target within the range of 750-850nm, the p-light reflectivity is 100%, and the group delay dispersion GDD is-200 fs2Through a membraneThe system design software optimizes the initial film structure until the film system structure meeting the design requirements is obtained.
The specific operation steps of the example are as follows:
1. ultrasonically cleaning a 0.5mm quartz glass substrate in an acetone solution for 15 minutes, repeatedly washing the quartz glass substrate with deionized water after taking out, and drying the quartz glass substrate.
2. And uniformly coating the photoresist on the front surface of the substrate by adopting a spin coating method, wherein the thickness of the photoresist is about 450-550 nm.
3. And (3) exposing by adopting a laser holographic interference technology, and soaking the exposed substrate in a developing solution for 10-30 seconds to obtain a two-dimensional array structure with the period of 400nm, the height of 300nm and the duty ratio of 1.
4. And transferring the prepared mask pattern to the surface of the quartz glass substrate by using a reactive ion etching technology to obtain the nano-structure array. As shown in FIG. 2, the period is 400nm, the height is 300nm, and the duty ratio is 1. Fig. 3 shows transmittance after the microstructure is prepared.
5. And depositing a chirped film system meeting the design requirement on the back of the substrate by adopting a double-ion-beam sputtering deposition technology. FIG. 4 is a graph of dispersion curve and reflectance curve of a chirped film system. After the anti-reflection microstructure is carved, the surface transmittance is increased from 96.5 percent to more than 99.9 percent, and the optical loss is greatly reduced. And since the incident medium is quartz glass, the dispersion oscillation of the back chirped film system is only one sixth of that of the air medium incident chirped mirror as shown in fig. 4.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (5)
1. A microstructure low-oscillation back-coated chirped mirror is characterized in that: the structure of the chirp medium film is A/M/G/C, wherein A represents an air layer, M represents an anti-reflection microstructure, G represents a substrate, C represents a chirp medium film system, the anti-reflection microstructure is a periodic array structure, and the chirp medium film system structure is formed by alternately depositing high-refractive index materials and low-refractive index materials;the chirped mirror structure expression is A/M/G/(HxL) ^ M (xHL) ^ n (HL) ^ k, wherein A represents an air layer, M represents an anti-reflection microstructure, G represents a substrate, H is a high-refractive-index material with the optical thickness of lambda/4, L is a low-refractive-index material with the optical thickness of lambda/4, n and M are the cavity periodicity, x is the cavity thickness, and k is the high-reflectivity film periodicity; the substrate material is quartz glass, K9, BK7 or CaF2The thickness is less than 0.5mm, and the medium thin film material with low refractive index in the chirp film system is SiO2。
2. The microstructured low-oscillation backside coated chirped mirror structure according to claim 1, wherein the number of periods k of the high reflectivity film is selected from a range of 7 to 20, the thickness x of the cavity is between 1.2 and 3, and the number of periods m, n of the cavity is between 5 and 15.
3. The microstructured low-oscillation backside coated chirped mirror of claim 1, wherein: the medium thin film material with high refractive index in the chirped film system is TiO2，Nb2O5，Ta2O5，HfO2，ZrO2Fluoride, sulfide, or Si.
4. The microstructured low-oscillation backside coated chirped mirror of claim 1, wherein: each unit of the periodic array structure is in a shape of a cuboid, a cylinder, a cone, a truncated cone, a pyramid or a parabolic cone.
5. A method of making the microstructured low-oscillation backside coated chirped mirror of any one of claims 1 to 4, characterized in that: the method comprises the following steps:
step 1) spin-coating photoresist on a substrate, and preparing a required mask pattern by adopting a laser holographic interference technology;
step 2) transferring the mask prepared in the step 1 onto a substrate by adopting a reactive ion beam etching technology to prepare the periodic array structure, wherein each unit of the periodic array structure is in a cuboid, a cylinder, a cone, a truncated cone, a pyramid or a parabolic cone;
and 3) depositing a chirped film system on the back surface of the substrate with the periodic array structure prepared in the step 2.
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| CN112666641B (en) * | 2021-01-18 | 2022-06-28 | 中国科学院上海光学精密机械研究所 | Design method of broadband low-dispersion chirped mirror |
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