A high-stability laser based on SBS standing-wave cavity

Abstract

The present invention proposes a high-stability laser based on an SBS standing-wave cavity. The laser comprises a seed source, an optical isolator, a polarizer, a quarter-wave plate, and an SBS pulse compressor, arranged in sequence. The centers of the seed source, optical isolator, polarizer I, quarter-wave plate, and SBS pulse compressor are arranged on the same horizontal line, with polarizer I tilted at a 56° angle. The seed source generates single-longitudinal-mode linearly polarized pump light, which passes through the optical isolator, polarizer, and quarter-wave plate in sequence before being transmitted to the SBS pulse compressor. While achieving a pulse width conversion from nanoseconds to hundreds of picoseconds, the present invention utilizes a standing-wave cavity structure to effectively improve the waveform jitter of the Stokes seed light, further narrow the seed light, and improve the output energy reflectivity. This significantly improves the energy and waveform stability of the output pulse compared to traditional structures, enabling high-power, high-stability, short-pulse laser output.

Description

Technical Field

[0001] The present invention relates to the field of nonlinear optics, and in particular to a high-stability laser based on an SBS (stimulated Brillouin scattering, SBS) standing wave cavity. Background Art

[0002] In recent years, high-power, 100-picosecond laser pulses with stable output pulse energy and pulse width have found important and widespread applications in inertial confinement fusion, space debris detection, laser precision machining, and laser medical treatment. In the impact ignition scheme of laser inertial confinement fusion, multiple stable, high-energy, high-power 100-picosecond lasers are required to simultaneously act on a deuterium-tritium target pellet filled with fuel to cause fusion and release enormous energy. In industrial laser processing, high-peak-power, high-stability 100-picosecond pulses can achieve "cold processing" with micron-level precision, generate less vibration during processing, reduce the roughness of the processed surface, and improve processing efficiency. In laser medical treatment, laser pulses with a duration of 100 picoseconds are far more effective in treating pigment spots than laser pulses with a duration of nanoseconds, greatly improving the efficiency of disease treatment.

[0003] SBS pulse compression technology can compress laser pulses of tens of nanoseconds to hundreds of picoseconds. Nanosecond pump light is incident on a Brillouin medium cell, generating a backward Stokes seed light. Under the modulation of the electrostrictive force, the seed light couples with the pump light and extracts the remaining energy. Because the seed light front extracts most of the energy of the pump light, a seed light with a steep front and narrow pulse width of hundreds of picoseconds can be obtained. This technology has become a hot research topic in recent years due to its simple structure, high beam quality, and high output energy. Currently, the focused single-cell structure suffers from optical breakdown, tail modulation, and low pulse compression rate at high pump power densities. The independent dual-cell structure, on the other hand, is cumbersome to install and makes optical path adjustment more difficult.

[0004] For example, the Chinese invention application with publication number CN114421270A discloses a Brillouin laser and a method for generating Brillouin lasers. The Brillouin laser disclosed in this invention includes a wavelength-tunable light source, a circulator, an optical fiber, and an optical microcavity. The wavelength-tunable light source is used to provide pump light. The optical fiber extends from the second end of the circulator to the optical microcavity. The optical fiber extending to the optical microcavity includes a tapered structure, and the optical fiber is coupled to the optical microcavity through the tapered structure. The pump light passes through the circulator and is coupled into the optical fiber. The pump light is coupled into the optical microcavity through the tapered structure. The wavelength and power of the pump light and the distance between the tapered structure and the optical microcavity are adjusted so that the pump light excites Brillouin laser light in the optical microcavity, and the pump light and the Brillouin laser light are in different optical mode families of the optical microcavity. The Brillouin laser light is coupled into the optical fiber, input from the second end of the circulator, and output from the third end of the circulator. The technical solution of the embodiments of the present invention can achieve on-chip integrated, low-noise, high-power, cascade-free Brillouin laser output. However, this embodiment is an integrated fiber laser with an output power of only mW level, and there is no mention of the laser having the effect of improving the output waveform; while the output power of this patent can reach MW level, while achieving the conversion of pulse width from nanoseconds to hundreds of picoseconds, it also improves the stability of the output pulse waveform and output energy. Summary of the Invention

[0005] In response to the technical problems of difficult adjustment, complicated device and low pulse compression efficiency of pulse compressors in existing lasers, the present invention proposes a high-stability laser based on an SBS standing wave cavity, which realizes the conversion of pulse width from nanoseconds to hundreds of picoseconds while improving the waveform jitter problem of the output pulse under high power density pumping, and improving the stability of the output pulse waveform and output energy.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A high-stability laser based on an SBS standing wave cavity is characterized by comprising a seed source, an optical isolator, a polarizer, a quarter-wave plate and an SBS pulse compressor arranged in sequence, wherein the centers of the seed source, the optical isolator, the polarizer I, the quarter-wave plate and the SBS pulse compressor are arranged on the same horizontal line, and the polarizer I is tilted at an angle of 56°; the seed source generates single-longitudinal-mode linearly polarized pump light, which is converted into circularly polarized light through the optical isolator, the polarizer and the quarter-wave plate in sequence, and finally transmitted to the standing wave cavity of the SBS pulse compressor to stabilize the phase of the generated parallel light beam and simultaneously achieve energy amplification and pulse width compression of the generated Stokes light.

[0008] The optical isolator includes a polarizer II, a Faraday rotator and a half glass plate arranged in sequence. The centers of the polarizer II, the Faraday rotator and the half glass plate are arranged on the same horizontal line, and the tilt angle of the polarizer II is 56°.

[0009] The SBS pulse compressor includes a beam reduction system, a Brillouin amplifier cell, a collimation system, a partial reflector, a positive lens and a Brillouin generating cell, which are arranged in sequence. The centers of the beam reduction system, the Brillouin amplifier cell, the collimation system, the partial reflector, the positive lens and the Brillouin generating cell are arranged on the same horizontal line, and the partial reflector maintains a normal incidence relationship with the pump light.

[0010] The beam reduction system comprises a positive lens and a negative lens which are arranged in sequence, and the centers of the positive lens, the negative lens and the Brillouin amplification cell are arranged on the same horizontal line.

[0011] The collimating system comprises a first pinhole diaphragm and a second pinhole diaphragm which are arranged in sequence, and the centers of the first pinhole diaphragm, the second pinhole diaphragm and the Brillouin amplification cell are arranged on the same horizontal line.

[0012] The incident surface of the partial reflector is coated with a partial reflective film, and the output surface of the partial reflector is coated with an anti-reflective film I, and the transmittance of the anti-reflective film I is greater than the reflectivity of the partial reflective film.

[0013] The length of the Brillouin amplifier cell L1≥τ p c / 2n, the distance d between the Brillouin amplifier cell and the Brillouin generator cell and the focal length F of the positive lens have the following constraints:

[0014] d+F≤τ p c / 4n

[0015] Among them, τ p is the pump light pulse width; c is the speed of light; n is the refractive index of the Brillouin medium.

[0016] The front and rear windows of the Brillouin amplifier cell and the Brillouin generator cell are both coated with anti-reflection film II, and the Brillouin amplifier cell and the Brillouin generator cell are both filled with SBS active medium.

[0017] The working method of the SBS pulse compressor is as follows: the circularly polarized light is incident on a partial reflector through a Brillouin amplifier cell and a collimation system of a beam reduction system; a partially parallel light beam is reflected by the partial reflector to form an antiparallel light beam; the antiparallel light beam is incident on a Brillouin amplifier cell through the collimation system and interferes with the circularly polarized light in the Brillouin amplifier cell, causing the Brillouin amplifier cell to form a standing wave cavity; the standing wave generated by the coherence of the parallel light beam and the circularly polarized light causes density modulation of the medium, stabilizing the phase and amplification process of the parallel light beam and suppressing waveform broadening; the circularly polarized light not reflected by the partial reflector propagates along the original direction, is focused by a positive lens and enters a Brillouin generating cell; the incident light power density in the Brillouin generating cell reaches the SBS threshold, thereby generating backscattered Stokes light; the Stokes light enters the Brillouin amplifier cell again, achieving energy amplification and pulse width compression in the standing wave cavity.

[0018] The beneficial effects of the present invention are as follows: a high-stability laser based on an SBS compact dual-cell standing-wave cavity is proposed for the first time, which realizes the conversion of pulse width from nanoseconds to hundreds of picoseconds. The standing-wave cavity structure is used to effectively improve the waveform jitter problem of the Stokes seed light, further narrow the seed light, and improve the output energy reflectivity. The energy and waveform stability of the output pulse are greatly improved compared with the traditional structure, thereby realizing high-power and high-stability short-pulse laser output. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 It is a structural schematic diagram of the present invention.

[0021] Figure 2 for Figure 1 Schematic diagram of the structure of the SBS pulse compressor shown.

[0022] In the figure, 1 is the seed source, 2 is the optical isolator, 3 is the polarizer, 4 is the quarter-wave plate, 5 is the SBS pulse compressor, 5-1 is the beam reduction system, 5-2 is the Brillouin amplifier cell, 5-3 is the collimation system, 5-4 is the partial reflection mirror, 5-5 is the positive lens, 5-6 is the Brillouin generating cell, 5-1-1 is the positive lens, 5-1-2 is the negative lens, 5-3-1 is the first pinhole aperture, and 5-3-2 is the second pinhole aperture. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0024] like Figure 1As shown, the high-stability laser based on the SBS standing-wave cavity includes a seed source 1, an optical isolator 2, a polarizer I 3, a quarter-wave plate 4, and an SBS pulse compressor 5, arranged in sequence. The centers of the seed source 1, optical isolator 2, polarizer I 3, quarter-wave plate 4, and SBS pulse compressor 5 are co-located. Seed source 1 is used to generate single-longitudinal-mode linearly polarized pump light. Optical isolator 2 includes a polarizer II, a Faraday rotator, and a half-glass, arranged in sequence. The centers of polarizer II, Faraday rotator, and half-glass are co-located, and polarizer II is tilted at a 56° angle. Polarizer II transmits forward P-polarized light and reflects reverse S-polarized light. The Faraday rotator rotates the polarization planes of both forward and reverse incident light by 45° in the same direction. The half-glass modulates the polarization state of light passing through the rotator back to P-polarized light and rotates the polarization state of the reverse incident light by 45° in a different direction, converting it to S-polarized light after passing through the rotator. Optical isolator 2 ensures unidirectional transmission of the light beam, preventing backward Stokes pulses or unpumped pump light from returning to the seed source 1 and damaging it. After passing through optical isolator 2, the pump light enters polarizer I 3, which is tilted at 56°. Polarizer I 3 analyzes the pump light. Setting the tilt angle at 56° ensures that the light is incident at the Brewster angle, ensuring that all transmitted light is P-polarized. The analyzed pump light then enters quarter-wave plate 4 and is converted to circularly polarized light. Subsequently, the circularly polarized light enters the pulse compressor 5 to achieve pulse compression and energy conversion, and output high-power and high-stability hundred-picosecond pulses.

[0025] like Figure 2 As shown, the SBS pulse compressor 5 includes a beam reduction system 5-1, a Brillouin amplifier cell 5-2, a collimator system 5-3, a partial reflector 5-4, a positive lens 5-5, and a Brillouin generator cell 5-6, which are arranged in sequence. The centers of the beam reduction system 5-1, the Brillouin amplifier cell 5-2, the collimator system 5-3, the partial reflector 5-4, the positive lens 5-5, and the Brillouin generator cell 5-6 are arranged on the same horizontal line, and the partial reflector 5-4 always maintains a normal incidence relationship with the pump light. Among them, the main function of the beam reduction system 5-1 is to increase the optical power density by reducing the spot area. The beam reduction system 5-1 includes a positive lens 5-1-1 and a negative lens 5-1-2, which are arranged in sequence. The centers of the positive lens 5-1-1 and the negative lens 5-1-2 are arranged on the same horizontal line. By combining the positive lens 5-1-1 and the negative lens 5-1-2, the focal length combination of the lens group is adjusted to obtain a suitable spot area. To avoid damaging the optical components in the subsequent optical path, the spot shape and spot diameter in the near field and far field after the beam reduction system 5-1 need to be measured when building the optical path to ensure that the circularly polarized light is converted into a parallel beam with good beam quality after passing through. The length L1 of the Brillouin amplifier cell 5-2 is ≥ τ pc / 2n, the distance d between the Brillouin amplifier cell 5-2 and the Brillouin generator cell 5-6 and the focal length F of the positive lens 5-1-1 have the following constraints:

[0026] d+F≤τ p c / 4n

[0027] Among them, τ p is the pump light pulse width; c is the speed of light; n is the refractive index of the Brillouin medium.

[0028] The front and rear windows of the Brillouin amplifier cell 5-2 are coated with antireflection coatings to prevent interfering return light from the window mirror. The cell is filled with a low-absorption, high-load, and short-phonon-lifetime SBS-active medium, providing a venue for energy conversion in the SBS process. The collimation system 5-3 comprises a first aperture 5-3-1 and a second aperture 5-3-2, arranged in sequence. The centers of the first and second apertures 5-3-1 and 5-3-2 are aligned horizontally to ensure collinear interference between the forward pump light and the antiparallel beam within the Brillouin amplifier cell 5-2, forming a coherent standing wave cavity. The incident surface of the partial reflector 5-4 is coated with a partial reflective coating, which reflects a portion of the parallel beam into the Brillouin amplifier cell. The output surface is coated with antireflection coating I to prevent interfering return light from the antiparallel beam. A positive lens 5-5 focuses the parallel beam within the medium. The Brillouin generating cell 5-6 primarily serves as a venue for energy exchange.

[0029] Specifically, circularly polarized light travels from beam reduction system 5-1 through Brillouin amplifier cell 5-2 and collimation system 5-3, entering partial reflector 5-4. Part of the parallel beam is reflected by partial reflector 5-4 to form an antiparallel beam. This antiparallel beam then travels through collimation system 5-3 and enters Brillouin amplifier cell 5-2, where it interferes with the circularly polarized light within Brillouin amplifier cell 5-2, forming a standing wave cavity within the cell. The standing wave generated by the coherence of the parallel and circularly polarized light modulates the density of the medium, further stabilizing the phase of the parallel beam and the amplification process. This effectively suppresses waveform broadening, further narrows the waveform, and reduces smearing and waveform jitter. The circularly polarized light not reflected by the partial reflector 5-4 propagates along the original direction, is focused by the positive lens 5-5 and enters the Brillouin generating cell 5-6. As the spot area decreases sharply, the incident light power density in the Brillouin generating cell 5-6 quickly reaches the SBS threshold, thereby generating backscattered Stokes light. The Stokes light enters the Brillouin amplifier cell 5-2 again, and further realizes energy amplification and pulse width compression in the standing wave cavity.

[0030] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-stability laser based on an SBS standing wave cavity, characterized by: The invention comprises a seed source (1), an optical isolator (2), a polarizer I (3), a quarter-wave plate (4) and an SBS pulse compressor (5) which are arranged in sequence, wherein the centers of the seed source (1), the optical isolator (2), the polarizer I (3), the quarter-wave plate (4) and the SBS pulse compressor (5) are arranged on the same horizontal line, and the polarizer I (3) has an inclination angle of 56°; The seed source (1) generates a single longitudinal mode linearly polarized pump light, which is converted into circularly polarized light through an optical isolator (2), a polarizer I (3), and a quarter wave plate (4) in sequence, and is finally transmitted to the standing wave cavity of an SBS pulse compressor (5) to stabilize the phase of the generated parallel light beam and simultaneously achieve energy amplification and pulse width compression of the generated Stokes light. The SBS pulse compressor (5) comprises a beam reduction system (5-1), a Brillouin amplifier cell (5-2), a collimating system (5-3), a partial reflector (5-4), a positive lens (5-5) and a Brillouin generating cell (5-6) which are arranged in sequence. The centers of the beam reduction system (5-1), the Brillouin amplifier cell (5-2), the collimating system (5-3), the partial reflector (5-4), the positive lens (5-5) and the Brillouin generating cell (5-6) are arranged on the same horizontal line, and the partial reflector (5-4) maintains a normal incidence relationship with the pump light. The length of the Brillouin amplifier cell (5-2) L 1 ≥ τ p c / 2 n ,in, τ p is the pump light pulse width; c is the speed of light; n is the refractive index of the Brillouin medium.

2. The high-stability laser based on the SBS standing wave cavity according to claim 1, characterized in that: The optical isolator (2) comprises a polarizing plate II, a Faraday rotator and a half glass plate arranged in sequence, wherein the centers of the polarizing plate II, the Faraday rotator and the half glass plate are arranged on the same horizontal line, and the tilt angle of the polarizing plate II is 56°.

3. The high-stability laser based on the SBS standing wave cavity according to claim 1 or 2, characterized in that: The beam reduction system (5-1) includes a positive lens (5-1-1) and a negative lens (5-1-2) arranged in sequence, and the centers of the positive lens (5-1-1), the negative lens (5-1-2) and the Brillouin amplifier cell (5-2) are arranged on the same horizontal line.

4. The high-stability laser based on the SBS standing wave cavity according to claim 3, characterized in that: The collimation system (5-3) includes a first pinhole diaphragm (5-3-1) and a second pinhole diaphragm (5-3-2) arranged in sequence, and the centers of the first pinhole diaphragm (5-3-1), the second pinhole diaphragm (5-3-2) and the Brillouin amplifier cell (5-2) are arranged on the same horizontal line.

5. The high-stability laser based on the SBS standing wave cavity according to claim 4, characterized in that: The incident surface of the partial reflector (5-4) is coated with a partial reflective film, and the output surface of the partial reflector (5-4) is coated with an anti-reflective film I, and the transmittance of the anti-reflective film I is greater than the reflectivity of the partial reflective film.

6. The high-stability laser based on the SBS standing wave cavity according to claim 5, characterized in that: The distance between the Brillouin amplifier cell (5-2) and the Brillouin generator cell (5-6) d Focal length of positive lens (5-1-1) F With the following constraints: d + F ≤ τ p c / 4 n 。 7. The high-stability laser based on the SBS standing wave cavity according to any one of claims 4 to 6, characterized in that: The front and rear windows of the Brillouin amplifier cell (5-2) and the Brillouin generator cell (5-6) are both coated with antireflection film II, and the Brillouin amplifier cell (5-2) and the Brillouin generator cell (5-6) are both filled with SBS active medium.

8. The high-stability laser based on the SBS standing wave cavity according to claim 7, characterized in that: The working method of the SBS pulse compressor (5) is as follows: the circularly polarized light is incident on a partial reflector (5-4) from a beam reduction system (5-1) via a Brillouin amplifier cell (5-2) and a collimation system (5-3); a partially parallel light beam is reflected by the partial reflector (5-4) to form an antiparallel light beam; the antiparallel light beam is incident on a Brillouin amplifier cell (5-2) via the collimation system (5-3) and interferes with the circularly polarized light in the Brillouin amplifier cell (5-2), so that the Brillouin amplifier cell (5-2) forms a standing wave cavity; The standing wave generated by the coherence of the parallel light beam and the circularly polarized light causes density modulation of the medium, which stabilizes the phase and amplification process of the parallel light beam and suppresses the broadening of the waveform; the circularly polarized light that is not reflected by the partial reflector (5-4) propagates along the original direction, is focused by the positive lens (5-5) and enters the Brillouin generating cell (5-6), and the incident light power density in the Brillouin generating cell (5-6) reaches the SBS threshold, thereby generating backscattered Stokes light, which enters the Brillouin amplifying cell (5-2) again, realizing energy amplification and pulse width compression in the standing wave cavity.

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