CN110391583B

CN110391583B - Saturable absorber based on non-stoichiometric transition metal oxide film and preparation method thereof

Info

Publication number: CN110391583B
Application number: CN201910596429.4A
Authority: CN
Inventors: 张多多; 刘小峰; 邱建荣
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2019-07-03
Filing date: 2019-07-03
Publication date: 2020-08-18
Anticipated expiration: 2039-07-03
Also published as: CN110391583A

Abstract

The invention discloses a saturable absorber based on a non-stoichiometric transition metal oxide film and a preparation method thereof. The saturable absorber mainly comprises a substrate, a non-stoichiometric transition metal oxide layer and a surface layer; the saturable absorber includes both a transmissive type and a reflective type. Wherein the substrate comprises an inorganic transparent substrate such as sapphire, quartz glass and the like and a coating film thereon; the transition metal oxide comprises TiO_2‑x、VO_2‑x、ZrO_2‑x、Nb₂O_5‑xEtc.; the operating band can cover the visible mid-infrared band due to the different materials used. The invention provides a brand-new saturable absorber for various pulse lasers and a preparation method thereof, which have the characteristics of simple preparation method, low cost, high laser damage threshold value and the like, can be widely applied to various lasers such as solid lasers, optical fiber lasers, semiconductor lasers and the like, and is used for generating the shortest laser pulse which can reach hundreds of femtoseconds.

Description

Saturable absorber based on non-stoichiometric transition metal oxide film and preparation method thereof

Technical Field

The invention belongs to the fields of nonlinear optical thin film materials and devices, laser materials and the like, and particularly relates to a saturable absorber based on a non-stoichiometric transition metal oxide thin film and a preparation method thereof.

Background

Pulsed lasers are widely used in the fields of laser manufacturing, medical treatment, precision spectroscopy, and the like. The pulse laser can be generated by an active and passive modulation mode, and mainly comprises a mode locking mode working mode and a Q modulation working mode, wherein the shortest mode locking pulse can reach a magnitude of several femtoseconds, and the Q modulation pulse has higher pulse energy. Active modulation techniques are currently mainly implemented by introducing acousto-optic or electro-optic modulators, while passive modulation includes kerr lenses and saturable absorbers. At present, the introduction of saturable absorbers in the laser resonator to achieve pulsed output by means of passive modulation is considered to be the most efficient and economical method of pulsed laser generation.

After only 6 years of first laser invention, scientists achieved pulsed laser output in Nd-doped glass lasers using organic dyes as saturable absorbers. In the last decades, various saturable absorbers have been developed, and pulsed laser output has been realized in different lasers, and these saturable absorber materials include dyes, doped glass, various carbon nanomaterials (such as graphene and carbon nanotubes), and various two-dimensional materials and topological insulator materials reported in recent years. Studies have shown that the performance of the laser pulse output is strongly dependent on the nonlinear optical properties of the saturable absorber employed, including saturable absorption intensity, modulation depth, response time, etc.

However, the stability of various saturable absorbers based on low-dimensional materials reported in recent years is not ideal enough, and the pulse output performance and the service life of the laser are greatly influenced. Therefore, although various low-dimensional material systems can easily realize Q-switched or mode-locked pulse output at present, and the working waveband covers the visible middle infrared light region, the pulse performance obtained by the saturable absorbers is not ideal in indexes such as pulse energy and stability, and the laser damage threshold is low, and the factors are still the main bottlenecks in realizing industrialization. At present, a commercial saturable absorber is monopolized by SESAM developed by Batop corporation of switzerland, the saturable absorber is based on semiconductor thin film materials, mainly comprises III-V group semiconductors, and the preparation process depends on molecular beam epitaxy technology, so that the requirement on equipment is high, the cost is high, and on the other hand, the saturable absorber has a limited working waveband and is difficult to realize broadband light modulation. Therefore, it is urgently required to develop a high-performance saturable absorber which can be prepared at low cost and has high stability, thereby reducing the production cost of the pulse laser to some extent.

Disclosure of Invention

In order to solve the problems in the background art, the invention provides a saturable absorber based on a non-stoichiometric transition metal oxide thin film and a preparation method thereof, wherein the saturable absorber is used for various solid and optical fiber lasers, is simple to prepare, has low cost, and has excellent saturable absorption performance and higher laser damage threshold.

The invention adopts the following technical scheme:

saturable absorber based on non-stoichiometric transition metal oxide film

The saturable absorber mainly comprises a substrate, a non-stoichiometric transition metal oxide layer and a surface layer; the saturable absorber includes a transmissive saturable absorber and a reflective saturable absorber.

The non-stoichiometric transition metal oxide layer is one or a mixture of more than two of TiO2-x, VO2-x, ZrO2-x or Nb2O5-x (x is 0-1).

The substrate of the transmission type saturable absorber is a transparent material substrate in an infrared or visible light wave band, and the transmission type saturable absorber has no surface layer or the surface layer is a dielectric antireflection film or an antireflection film.

The substrate of the reflective saturable absorber is a transparent material substrate in the infrared or visible light band and a reflective layer coated thereon, and the reflective layer includes a noble metal reflective layer or a dielectric multilayer film reflective layer. The reflective saturable absorber has no surface layer or the surface layer is a dielectric high reflection film.

The transparent material substrate is quartz glass, silicon Si sheet and sapphire Al₂O₃A sheet, a quartz glass sheet, a CaF2 sheet, or a metal sulfide semiconductor single crystal (e.g., ZnSe).

The saturable absorber is used for mode locking and Q-switching pulse generation of different kinds of pulse lasers (such as a solid laser, a fiber laser and a semiconductor laser); the saturable absorber has a working band coverage of 0.5-5.0 microns.

The non-stoichiometric transition metal oxide thin film may exhibit saturable absorption effects in the 0.5-5 micron band.

Preparation method of saturable absorber based on non-stoichiometric transition metal oxide film

The preparation method of the permeable saturable absorber comprises the following steps: depositing an oxide film on a substrate by other methods such as magnetron sputtering or laser pulse deposition, then placing the substrate in a reducing atmosphere for heat treatment to obtain an oxide film with a non-stoichiometric ratio, and finally depositing a surface layer on the surface of the oxide film with the non-stoichiometric ratio to obtain a permeable saturable absorber; the surface layer may or may not be an antireflection film.

The preparation method of the reflection-type saturable absorber comprises the following steps: depositing a high-reflection film on a substrate by other methods such as magnetron sputtering or laser pulse deposition, depositing an oxide film on the surface of the high-reflection film, placing the high-reflection film in a reducing atmosphere for heat treatment to obtain an oxide film with a non-stoichiometric ratio, and depositing a surface layer on the surface of the oxide film with the non-stoichiometric ratio to obtain a reflective saturable absorber; the surface layer may be a highly reflective film or not.

The invention has the beneficial effects that:

(1) the saturable absorber based on the transition metal oxide can be prepared in large quantity by common equipment (such as magnetron sputtering and pulsed laser deposition), and the obtained solid film has a large laser damage threshold value which is 100mJ/cm². The low-cost saturable absorber can reduce the research and manufacturing cost of the pulse laser to a certain extent.

(2) The invention can realize the modulation of the absorption spectrum and the nonlinear optical property of the material by controlling the stoichiometry of the material, thereby providing a new idea for the design and development of saturable absorber materials.

(3) The invention can be used in various pulse lasers to generate mode-locked and Q-switched pulse output and the fields of laser pulse shaping and the like.

Drawings

FIG. 1 shows the TiO base corresponding to example 1_2-xZ-scan test curve of saturable absorber.

FIG. 2 shows a TiO-based material according to example 1_2-xThe transmittance of the transmissive saturable absorber of (3) and the incident laser power.

FIG. 3 shows the TiO base corresponding to example 1_2-xSchematic structural diagram of the transmissive saturable absorber of (1).

FIG. 4 shows ZrO based alloys according to example 5_2-xSchematic structural diagram of the transmissive saturable absorber of (1).

FIG. 5 shows TiO-based materials of example 7_2-xThe structure of the reflective saturable absorber of (1) is schematically illustrated.

Detailed Description

The invention is further illustrated with reference to the following figures and examples, without thereby limiting the scope of protection of the invention.

The invention mainly comprises a substrate, a non-stoichiometric transition metal oxide thin film layer and a surface layer, and comprises a transmission type and a reflection type, wherein the most important transition metal oxide comprises one of the following materials: TiO2_2-x、VO_2-x、ZrO_2-x、Nb₂O_5-x(x＝0～1)。

Example 1

This example preparation of a non-stoichiometric TiO base_2-xThe permeable saturable absorber of the film is used for a 1.5 micron wave band optical fiber pulse laser.

(1) Taking a quartz glass substrate with the thickness of 0.5 mm and the length and the width of 20 mm, and growing a layer of TiO with the thickness of 50nm by a magnetron sputtering method₂A film.

(2) Carrying out heat treatment on the film obtained in the step (1) in a hydrogen atmosphere for 10 hours at the temperature of 800 ℃, thereby obtaining TiO_2-xA film.

(3) Growing a layer of Al on the surface of the film obtained in the step (2) through magnetron sputtering₂O₃20nm in thickness, the Al₂O₃Only has the protection function and does not have the functions of permeability increasing and reaction reducing.

Based on TiO_2-xThe saturable absorber of (A) shows saturability in the range of 1.5 to 3.0 μmAbsorption, wherein the modulation depth of the 1.5 micron wave band is 2.5%.

FIGS. 1 and 2 are Z-scan curves and transmittance and incident laser power curves for a saturable absorber, with a test wavelength of 1.5 microns; FIG. 3 is a diagram based on TiO_2-xA thin film structure of a saturable absorber; the Z-scan curve of the saturable absorber in FIG. 1 demonstrates that the TiO base is based on_2-xThe saturable absorber of (a) has excellent saturable absorption;

the application comprises the following steps: and (4) placing the saturable absorber device thin film obtained in the step (3) into two optical fiber connectors to serve as a passive modulation mode locking original piece, and realizing mode locking pulse output in an Er-doped fiber laser, wherein the pulse width is 530 femtoseconds.

Example 2

This example preparation of a non-stoichiometric TiO base_2-xThe thin film reflective saturable absorber is used for a solid laser with a wave band of 1.0 micron to realize Q-switched pulse output.

(1) Sapphire (Al) with thickness of 0.5 mm and length and width of 20 mm is selected₂O₃) A substrate, a layer of TiO is grown on the substrate material by Pulsed Laser Deposition (PLD) technique₂/SiO₂A high-reflection film (thickness of 500-700nm) and then growing TiO on the high-reflection film₂And the thickness of the film is 20 nm.

(2) Carrying out heat treatment on the film obtained in the step (1) in a reducing atmosphere at the temperature of 800 ℃ for 10 hours in the atmosphere of pure hydrogen (1MPa) to obtain TiO_2-xA film.

(3) Coating a layer of TiO on the surface of the film obtained in the step (2) by magnetron sputtering₂/SiO₂The reflectivity of the finally obtained saturable absorber in a 1-micron wave band is more than 98 percent, and the modulation depth is 0.7 percent.

The application comprises the following steps: the prepared saturable absorber is placed in a laser cavity, the used gain crystal is Yb: YAP, under a 980nm pump, pulse output of Q modulation is obtained, the laser wavelength is 1060nm, and the pulse width is 1.0 microsecond.

Example 3

The present embodiment utilizes laserVO-based preparation by optical pulse deposition technology_2-xThe film is a permeable saturable absorber, and the working wave band is covered by 1.5-5.0 microns.

(1) Selecting a silicon wafer with the thickness of 1 mm and the length and width of 20 mm as a substrate, and performing laser pulse deposition on the substrate to VO by reasonably controlling the atmosphere of a cavity_2-xThe film was deposited to a thickness of 50nm on the substrate surface.

(2) Then depositing a layer of MgF on the surface of the film obtained in the step (1) by a magnetron sputtering technology₂And (4) forming a layer to realize an anti-reflection effect. Tests show that the saturable absorber exhibits saturable absorption in the range of 1.5-5.0 microns, with a modulation depth of 15% at 3.6 microns.

The application comprises the following steps: based on the Er-ZBLAN fiber, the film prepared in the step (2) is used as a saturable absorber, so that Q-switched pulse output of a 3.6-micron wave band is obtained, and the pulse width is 3.0 microseconds.

Example 4

This example utilizes a sol-gel method for the preparation of Nb-based₂O_5-xThe film is a permeable saturable absorber, and the working wave band is covered by 1.5-5.0 microns.

(1) Selecting a silicon wafer with the thickness of 1 mm and the length and width of 20 mm as a substrate, and growing Nb with the thickness of 50nm on the substrate through sol-gel₂O_5-xThe process comprises three steps of spin coating at room temperature, drying at 100 ℃ and heat treatment at 600-900 ℃.

(2) Spin-coating a layer of SiO on the surface of the film obtained in the step (1) by a sol-gel method₂And a layer having a thickness of 800nm or less.

Tests have shown that the saturable absorber exhibits saturable absorption in the range of 1.5-5.0 microns, with modulation depths of 2 microns, 3 microns, and 3.5 microns of 25%, 20%, and 18%, respectively.

Example 5

This example preparation of a non-stoichiometric ZrO_2-xThe reflective saturable absorber of the thin film, its working wavelength band covers 1-3 microns.

(1) CaF with the thickness of 0.5 mm and the length and width of 20 mm is selected₂A substrate, a layer of silver (Ag) film is firstly grown on the substrate by a vacuum evaporation method, and then ZrO continues to grow on the silver (Ag) film₂The thickness of the film is controlled to be less than 20 nm.

(2) Heat treating the film obtained in step (1) in a reducing atmosphere at 800 deg.C for 10 hr to obtain ZrO, wherein the atmosphere is pure hydrogen (1MPa)_2-xA film.

(3) Coating a layer of TiO on the surface of the film obtained in the step (2) by magnetron sputtering₂/SiO₂High reflection film, resulting in a saturable absorber having the structure shown in fig. 4.

The reflectivity of the saturable absorber in a 1-3 micron wave band is more than 98 percent. Nonlinear optical tests show that the saturable absorption waveband of the optical fiber covers the interval of 1-3 microns, and the modulation depth of the optical fiber reaches 1.8% in the 2-micron waveband.

Example 6

This example preparation is based on non-stoichiometric Nb₂O_5-xThe reflective saturable absorber of the thin film covers 1.5-5 microns in the working wave band.

(1) Selecting a ZnSe substrate with the thickness of 0.5 mm and the length and width of 20 mm, firstly growing a layer of gold (Au) film on the substrate by a sputtering method, and then continuously growing Nb on the Au film by a magnetron sputtering method₂O_5-xThe thickness of the film is controlled below 50 nm.

(2) And (2) carrying out heat treatment on the film obtained in the step (1) in a reducing atmosphere at the temperature of 800 ℃ for 10 hours in the atmosphere of pure hydrogen (1 MPa).

(3) Coating a layer of TiO on the surface of the film obtained in the step (2) by magnetron sputtering₂The reflectivity of the saturable absorber obtained by the high-reflection film in a 1.5-5 micron wave band is more than 95%. Nonlinear optical tests show that the saturable absorption waveband covers the interval of 1-5 microns, and the modulation depth in the interval is 0.5% -3.5%.

Example 7

This example preparation based on TiO_2-xThe reflective saturable absorber of the film has an operating band of 1.5 microns.

(1) A silicon chip substrate with the thickness of 0.5 millimeter and the length and width of 20 millimeters is selected, a multilayer film Bragg reflector is grown on the silicon chip substrate by a molecular beam technology, and the reflection wavelength is 1.5 micrometers.

(2) Growing TiO on the film obtained in the step (1) by magnetron sputtering₂The thickness of the film is controlled to be less than 20 nm.

(3) Carrying out heat treatment on the film obtained in the step (2) in a reducing atmosphere at the temperature of 800 ℃ for 10 hours in the atmosphere of pure hydrogen (1MPa) to obtain TiO_2-xA film.

(4) Coating a layer of SiO on the surface of the film obtained in the step (3) by magnetron sputtering₂/TiO₂High reflection film, resulting in a saturable absorber having a structure as shown in fig. 5. The reflectivity of the finally obtained saturable absorber in a 1.5-micron wave band is more than 98%. Nonlinear optical testing indicated that the modulation depth was 1.5%.

Example 8

This example preparation is based on VO_2-xThe reflective saturable absorber of the film has an operating band of 2.0 microns.

(1) A ZnSe substrate with the thickness of 0.5 mm and the length and width of 20 mm is selected, a multilayer film Bragg reflector is grown on the ZnSe substrate by a molecular beam technology, and the reflection wavelength is 2.0 microns.

(2) Growing VO on the film obtained in the step (1) through magnetron sputtering₂The thickness of the film is controlled to be less than 20 nm.

(3) Heat treating the film obtained in step (2) in a reducing atmosphere at 700 deg.C for 10 hr₂/N₂Mixing the gas to obtain VO_2-xA film.

(4) Coating a layer of SiO on the surface of the film obtained in the step (3) by magnetron sputtering₂/TiO₂The reflectivity of the saturable absorber obtained by the high-reflection film in a 2.0 micron wave band is more than 98.5 percent. Nonlinear optical testing indicated that the modulation depth was 1.0%.

The above-described embodiments are intended to illustrate rather than to limit the invention, and all such modifications and variations are possible within the spirit of the invention and the scope of the appended claims.

Claims

1. A preparation method of a saturable absorber based on a non-stoichiometric transition metal oxide film adopts the saturable absorber based on the non-stoichiometric transition metal oxide film, and the saturable absorber mainly comprises a substrate, a non-stoichiometric transition metal oxide layer and a surface layer; the saturable absorber comprises a transmission type saturable absorber and a reflection type saturable absorber;

the non-stoichiometric transition metal oxide layer is TiO₂-x、VO₂-x、ZrO₂-x or Nb₂O₅-x is one or a mixture of two or more thereof;

the substrate of the transmission type saturable absorber is a transparent material substrate in an infrared or visible light wave band, and the transmission type saturable absorber has no surface layer or the surface layer is a dielectric antireflection film;

the substrate of the reflection type saturable absorber is a transparent material substrate in an infrared or visible light wave band and a high-reflection film growing on the transparent material substrate, and the high-reflection film comprises a gold coating, a silver coating and a multilayer Bragg reflection film; the surface layer of the reflective saturable absorber is not provided with or is a dielectric high-reflection film;

the transparent material substrate is silicon (Si) sheet or sapphire (Al)₂O₃) A sheet, a quartz glass sheet, a CaF2 sheet, or a metal sulfide semiconductor single crystal;

the saturable absorber is used for mode locking and Q-switched pulse generation of different kinds of pulse lasers; the working wave band of the saturable absorber covers 0.5-5.0 microns;

it is characterized in that the preparation method is characterized in that,

the preparation method of the permeable saturable absorber comprises the following steps: depositing an oxide film on a substrate through magnetron sputtering or laser pulse deposition, then placing the substrate in a reducing atmosphere for heat treatment to obtain an oxide film with a non-stoichiometric ratio, and finally depositing a surface layer on the surface of the oxide film with the non-stoichiometric ratio to obtain a permeable saturable absorber;

the preparation method of the reflection-type saturable absorber comprises the following steps: firstly, depositing a high-reflection film on a substrate through magnetron sputtering or laser pulse deposition, then depositing an oxide film on the surface of the high-reflection film, placing the high-reflection film in a reducing atmosphere for heat treatment to obtain an oxide film with a non-stoichiometric ratio, and finally depositing a surface layer on the surface of the oxide film with the non-stoichiometric ratio to obtain the reflective saturable absorber.