CN108493747A - 2 μm of high-energy pure-tone pulse lasers based on optical fiber solid Cascaded amplification - Google Patents

Abstract

A kind of 2 μm of high-energy pure-tone pulse lasers based on optical fiber solid Cascaded amplification.It using the continuous single-frequency seed source of low-power as front end, uses acousto-optic modulator by continuous single-frequency seed source copped wave for pulsed light, pulse repetition, pulsewidth and waveform after copped wave is flexibly controlled by controlling driving repetition, pulsewidth and the waveform of acousto-optic modulator.Subsequently pass through polarization maintaining optical fibre amplifier respectively and solid amplifier realizes the energy amplification of pure-tone pulse laser, it is final to realize 2 μm of high-energy pure-tone pulse laser outputs.The continuous single-frequency seed source single-frequency of low-power is stable and reliable for performance, strong antijamming capability；Prime uses polarization maintaining optical fibre amplifier, effectively improves the amplifying power of small signal；Rear class is amplified using solid, is easy to generate the pure-tone pulse laser output of high pulse energy and high-peak power.The laser structure is simple, system is stable, Parameter adjustable, not only adapts to general operating environment requirements, moreover it is possible to adapt to airborne and spaceborne requirement.

Description

2μm high-energy single-frequency pulse laser based on fiber solid-state cascade amplification

technical field

The invention belongs to the field of 2μm lasers, in particular to a 2μm high-energy single-frequency pulse laser based on optical fiber solid-state cascade amplification.

Background technique

2μm lasers are widely used in atmospheric and environmental monitoring, laser medical treatment, laser precision ranging, photoelectric countermeasures, laser radar and other fields. In the field of laser radar for Doppler wind measurement or remote sensing to detect atmospheric concentration, 2μm laser is used as its emission source, and its line width, frequency stability, single pulse energy, beam quality and other parameters directly determine the measurement accuracy and detection ability of laser radar. Therefore, the development of a narrow-linewidth, high-energy, and high-performance 2μm single-frequency pulsed laser is of great significance for improving the measurement accuracy, temporal and spatial resolution, and stability of the lidar system.

For single-frequency high-energy 2μm lasers, the common technical means is to use a seed injection oscillator to achieve single-frequency pulse output, and then use a solid-state amplifier to achieve high-energy output. This technology has made great progress in the past few decades, but its principle determines some inevitable shortcomings, which are mainly reflected in the following two points:

One is that the frequency stability of the laser pulse is determined by the frequency stability of the longitudinal mode of the driven cavity, and since the frequency of the longitudinal mode of the driven cavity has a random jitter relative to the frequency of the seed light, its frequency stability is compared to that of the The frequency stability of the seed light is poor;

The second is that the seed injection laser needs to achieve a narrow linewidth output, and the required pulse width is relatively wide, which requires a relatively long resonant cavity length, resulting in a complex laser structure and poor stability.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a 2 μm high-energy single-frequency pulse laser based on optical fiber solid-state cascade amplification. The spectral characteristics of the laser are determined by a low-power seed laser, which enables it to maintain good single-frequency characteristics even in complex external environments. Moreover, the laser can flexibly control parameters such as the repetition frequency, pulse width, and waveform of the output pulse, so as to meet different application requirements, especially difficult for seed injection lasers. The laser has simple structure, stable system, and adjustable parameters, which can not only meet the requirements of general working environment, but also meet the requirements of airborne and spaceborne.

Basic thought of the present invention is:

A low-power single-frequency seed source is used as the front end, which is converted into pulsed light after being chopped by an acousto-optic modulator. The energy amplification of the single-frequency pulse laser is realized through a polarization-maintaining fiber amplifier and a solid-state amplifier respectively, and finally a 2μm high-energy single-frequency pulse laser is realized. output. The single-frequency performance of low-power single-frequency seed source is stable and reliable, and the anti-interference ability is strong; the optical fiber amplifier is used in the front stage, which can effectively improve the amplification ability of small signals; The advantage of power can effectively avoid the nonlinear effect that is easy to occur in fiber amplification under high power, so as to achieve 2μm single-frequency, high-energy laser pulse output.

Technical solution of the present invention is as follows:

A 2μm high-energy single-frequency pulse laser based on fiber-optic solid-state cascade amplification, which is characterized in that its structure includes three parts: a single-frequency seed source, a fiber amplifier, and a solid-state amplifier:

The single-frequency seed source includes a single-frequency seed laser, and the first fiber isolator, the first beam combiner, the first gain fiber, and the second fiber isolator are sequentially arranged along the output direction of the seed laser, and the above-mentioned devices are sequentially welded together . The output end of the first optical fiber pump source is fused with the pump input end of the first beam combiner;

The optical fiber amplifier is provided with an optical fiber acousto-optic modulator, a second beam combiner, a second gain fiber, a fiber filter isolator, a third beam combiner, a third gain fiber, and a fiber collimator in sequence along the laser transmission direction. The above devices are welded together end to end. The output end of the second optical fiber pump source is fused with the pump input end of the second beam combiner, and the output end of the third optical fiber pump source is fused with the pump input end of the third beam combiner; the single-frequency seed The tail of the second optical fiber isolator of the source is fused with the head of the optical fiber acousto-optic modulator of the optical fiber amplifier;

The solid-state amplifier is sequentially arranged along the laser transmission direction with a first reflector placed at 45° to the optical path, a spatial acousto-optic modulator, a second reflector placed at 45° with the optical path, a first space isolator, and a first expander. Beam system, the first half-wave plate, end-pump gain crystal, the first 0° reflector, the first 45° prism reflector, the third reflector placed at 45° with the optical path, the second space isolator, The second beam expander system, the second half-wave plate, the side pump gain crystal, the second 0° reflector, and the second 45° prism reflector. The output laser light of the solid end-pump pump source enters the end-pump gain crystal through the coupling mirror and the first 0° reflector respectively from the end face. The output laser light from the solid-state side-pump pump source enters the side-pump gain crystal from the side.

The seed laser outputs single-frequency continuous low-power laser.

The fiber isolator prevents the amplified laser feedback from damaging the seed laser.

The fiber optic acousto-optic modulator chops continuous seed light into pulsed light.

The first gain fiber, the second gain fiber and the third gain fiber are double-clad doped thulium, holmium or thulium-holmium co-doped fibers.

The fiber filter isolator prevents subsequent amplified laser feedback from damaging the front-end device, and at the same time narrows the laser pulse line width.

The spatial acousto-optic modulator sets a gate switch for chopping, eliminating the impact of the pulse base on subsequent solid amplification.

The end-pump gain crystal and the side-pump gain crystal are gain crystals doped with thulium, holmium or co-doped with thulium and holmium.

The first half-wave plate and the second half-wave plate are used to adjust the polarization state of the laser.

The present invention has the following advantages:

1. The spectral performance of the laser is determined by the seed laser. Even in a complex external environment, the laser can still maintain good single-frequency characteristics.

2. The pulse repetition frequency, pulse width, waveform and other parameters of the laser can be flexibly controlled to meet different application requirements.

3. The laser has simple structure, stable system, and adjustable parameters, which can not only meet the requirements of general working environment, but also meet the requirements of airborne and spaceborne.

Description of drawings

Fig. 1 is a schematic diagram of the optical path of the 2 μm high-energy single-frequency pulse laser based on the fiber solid cascade amplification of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

Referring to FIG. 1, FIG. 1 is a schematic diagram of the optical path of the 2 μm high-energy single-frequency pulse laser based on the fiber solid cascade amplification of the present invention. It can be seen from the figure that the 2 μm high-energy single-frequency pulse laser of the present invention includes three parts: a single-frequency seed source, an optical fiber amplifier, and a solid-state amplifier:

The single-frequency seed source includes a single-frequency seed laser 1-1, and the first fiber isolator 1-2, the first beam combiner 1-4, and the first gain fiber are arranged in sequence along the output direction of the seed laser 1-1. 1-5. The second optical fiber isolator 1-6. The above devices are welded together end to end. The output end of the first optical fiber pump source 1-3 is fused with the pump input end of the first beam combiner 1-4;

The optical fiber amplifier is sequentially provided with an optical fiber acousto-optic modulator 2-1, a second beam combiner 2-3, a second gain fiber 2-4, a fiber filter isolator 2-5, and a third beam combiner along the laser transmission direction 2-7, third gain fiber 2-8, fiber collimator 2-9. The above devices are welded together end to end. The output end of the second optical fiber pumping source 2-2 is fused with the pumping input end of the second beam combiner 2-3, and the output end of the third optical fiber pumping source 2-6 is connected to the third beam combiner 2-7. The pump input end is fused; the tail of the second optical fiber isolator 1-6 of the single-frequency seed source is fused with the head of the optical fiber acousto-optic modulator 2-1 of the optical fiber amplifier;

The solid-state amplifier is sequentially arranged along the laser transmission direction with a first reflector 3-1 placed at 45° to the optical path, a spatial acousto-optic modulator 3-2, a second reflector 3-3 placed at 45° with the optical path, The first spatial isolator 3-4, the first beam expander system 3-5, the first half-wave plate 3-6, the end-pump gain crystal 3-7, the first 0° mirror 3-8, the first 45° prism mirror 3-11, third mirror 3-12 placed at 45° to the optical path, second space isolator 3-13, second beam expander system 3-14, second half-wave plate 3-15, side pump gain crystal 3-16, second 0° reflector 3-17, second 45° prism reflector 3-19. The output laser light of the solid-end pumping source 3-9 enters the end-pump gain crystal 3-7 through the coupling mirror 3-10 and the first 0° reflector 3-8 respectively. The output laser light of the solid-state side-pump pump source 3-18 enters the side-pump gain crystal 3-16 from the side.

The single-frequency seed laser 1-1 outputs single-frequency continuous low-power laser light.

The first fiber isolator 1-2 and the second fiber isolator 1-6 prevent the feedback of the amplified laser from damaging the seed laser.

The optical fiber acousto-optic modulator 2-1 chops the continuous seed light into pulsed light.

The first gain fiber 1-5, the second gain fiber 2-4 and the third gain fiber 2-8 are double-clad doped thulium, holmium or thulium-holmium co-doped fibers.

The fiber filter isolator 2-5 prevents subsequent amplified laser feedback from damaging front-end devices, and at the same time narrows the laser pulse linewidth.

The spatial acousto-optic modulator 3-2 sets a gate switch to perform chopping to eliminate the impact of the pulse base on the subsequent solid amplification.

The end-pump gain crystal 3-7 and the side-pump gain crystal 3-16 are gain crystals doped with thulium, holmium or co-doped with thulium and holmium.

The first half-wave plate 3-6 and the second half-wave plate 3-15 are used to adjust the polarization state of the laser.

Below is the parameter of a specific embodiment of the present invention:

The single-frequency seed source 1-1 uses a DFB seed laser with an output power of 5mW, a linewidth of less than 3MHz, and a wavelength of 2μm. The first gain fibers 1-5 are thulium-doped double-clad fibers with a core diameter of 6 μm, a numerical aperture of 0.22, and an inner cladding diameter of 125 μm. The first optical fiber pumping source 1-3 is continuously pumped by a laser diode with a center wavelength of 793nm, and the output power is 2W. The second gain fiber 2-4 is a thulium-doped double-clad fiber with a core diameter of 10 μm, a numerical aperture of 0.14, and an inner cladding diameter of 125 μm. The third gain fiber 2-8 is a thulium-doped double-clad fiber with a core diameter of 25 μm, a numerical aperture of 0.09, and an inner cladding diameter of 300 μm. The second optical fiber pumping source 2-2 and the third optical fiber pumping source 2-6 are laser diodes pumped by pulses with a center wavelength of 793 nm, the repetition frequency is set to 10 Hz, and the pumping pulse width is 1 ms. When the energy of the second optical fiber pumping source 2-2 is 4.2mJ and the energy of the third optical fiber pumping source 2-6 is 12mJ, the output energy of the optical fiber amplifier is 0.15mJ. The end-pump gain crystals 3-7 of the solid-state amplifier are rod-shaped Tm:Ho:LuLF crystals, in which Tm is doped by 6%, Ho is doped by 0.5%, the diameter is 3 mm, and the length is 15 mm. The pumping source 3-9 of the solid-end pump adopts a 793nm module with fiber-coupled output, the fiber core diameter is 400μm, the numerical aperture NA<0.17, the peak power is 600W, the pulse width is 1ms, and the repetition frequency is 10Hz. The pumping source 3-18 of the solid side pump adopts a 793nm Bar bar with a maximum output peak power of 100W and a pulse width of 1ms. In order to improve the output laser beam quality and laser energy, a laser diode is used to side-pump rod-shaped crystals. Five groups are radially evenly distributed, each group has 4 bars, and the total pump energy is 2J. The side-pump gain crystal 3-16 is a rod-shaped Tm:Ho:LuLF crystal, in which Tm is doped with 6% and Ho is doped with 0.5%. A typical single Bar is 10mm long, with a 1mm gap between the Bars. The gain bar is 45mm long and 4.5mm in diameter. Finally, it can output a single-frequency laser output with a pulse energy of 100mJ.

In addition to Tm, Ho:LLF, the laser gain medium of the present invention can also use other laser crystals doped with thulium and holmium; the corresponding pump source can be an LD pump source suitable for different crystal center wavelengths. According to the above, according to actual needs, based on the design idea and design principle of the present invention, the number of stages of fiber amplifiers and solid amplifiers can be changed to obtain a higher-energy single-frequency 2 μm pulse laser output.

Claims (7)

1. a kind of 2 μm of high-energy pure-tone pulse lasers based on optical fiber solid Cascaded amplification are characterized in that its structure includes single Frequency seed source, fiber amplifier, solid amplifier three parts：

The single-frequency seed source includes single-frequency seed laser (1-1), along the seed laser (1-1) outbound course successively Be head and the tail welding the first fibre optic isolater (1-2), the first bundling device (1-4), the first gain fibre (1-5) and the second optical fiber every From device (1-6), the pumping input terminal welding of the output end and the first bundling device (1-4) in the first pumped fiber source (1-3)；

The fiber amplifier is closed along the optical fiber acousto-optic modulator (2-1) that laser transmission direction is head and the tail welding successively, second Beam device (2-3), the second gain fibre (2-4), optical fiber filtering isolator (2-5), third bundling device (2-7), third gain fibre The pumping of (2-8) and fiber optic collimator mirror (2-9), the output end and the second bundling device (2-3) in the second pumped fiber source (2-2) inputs Hold welding, the output end in third pumped fiber source (2-6) and the pumping input terminal welding of third bundling device (2-7)；The list The tail portion of the second fibre optic isolater (1-6) of frequency seed source and the optical fiber acousto-optic modulator (2-1) of the fiber amplifier Head welding；

The solid amplifier is set gradually and the first speculum of light path placement at 45 ° (3-1), sky along laser transmission direction Between acousto-optic modulator (3-2), expand with the second speculum (3-3) of light path placement at 45 °, the first space isolator (3-4), first Beam system (3-5), the first half wave plate (3-6), end pump gain crystal (3-7), the one 0 ° of speculum (3-8), the one 45 ° Prism mirror (3-11) and the third speculum (3-12) of light path placement at 45 °, second space isolator (3-13), second Beam-expanding system (3-14), the second half wave plate (3-15), side pump gain crystal (3-16), the 2nd 0 ° of speculum (3-17), 2nd 45 ° of prism mirror (3-19).The output laser that solid end pumps pumping source (3-9) passes through coupling mirror (3-10), the respectively One 0 ° of speculums (3-8) from end face enter end pump gain crystal (3-7), solid side pump pumping source (3-18) output laser from Side approaching side pump gain crystal (3-16).

2. 2 μm of high-energy pure-tone pulse lasers according to claim 1 based on optical fiber solid Cascaded amplification, feature It is single-frequency seed laser (1-1) the output single-frequency continuous low power laser.

3. 2 μm of high-energy pure-tone pulse lasers according to claim 1 based on optical fiber solid Cascaded amplification, feature It is that continuous seed light copped wave is pulsed light by the optical fiber acousto-optic modulator (2-1).

4. 2 μm of high-energy pure-tone pulse lasers according to claim 1 based on optical fiber solid Cascaded amplification, feature Be the first gain fibre (1-5), the second gain fibre (2-4) and the third gain fibre (2-8) for thulium doped, holmium or The gain fibre that person's thulium holmium is co-doped with.

5. 2 μm of high-energy pure-tone pulse lasers according to claim 1 based on optical fiber solid Cascaded amplification, feature It is that the optical fiber filtering isolator (2-5) prevents from subsequently amplifying Laser feedback damage front-end devices, while narrows laser arteries and veins It breasts the tape width.

6. 2 μm of high-energy pure-tone pulse lasers according to claim 1 based on optical fiber solid Cascaded amplification, feature It is that space acousto-optic modulator (3-2) the setting door switch carries out copped wave, eliminates what pulse substrate amplified subsequent solid It influences.

7. 2 μm of high-energy pure-tone pulse lasers according to claim 1 based on optical fiber solid Cascaded amplification, feature It is that the end pump gain crystal (3-7) and side pump gain crystal (3-16) are the gain that thulium doped, holmium or thulium holmium are co-doped with Crystal.