An air-cooled tunable single-frequency pulsed slab laser

Abstract

The application discloses a kind of air-cooled type tunable single-frequency pulsed slab laser, belong to solid laser technical field.The method includes diode stack, pump shaping system, coupling cavity mirror, slab laser crystal, first mirror, film polarizer, wherein, the diode stack is as pump source;The pump shaping system is used to eliminate the slow axis direction non-uniformity of diode stack, and slab laser crystal is directly partially end-pumped based on coupling cavity mirror;The coupling cavity mirror, first mirror and film polarizer jointly constitute annular resonant cavity, and oscillation laser is repeatedly passed through slab laser crystal in the annular resonant cavity, and finally single-frequency pulsed laser is output via film polarizer.The application does not need continuous seed modulation or seed injection locking, and the system is simple and reliable, low in cost, and can be used as the large energy single-frequency pulsed laser source required by atmospheric detection.

Description

Technical Field

[0001] This invention belongs to the field of solid-state laser technology, specifically relating to an air-cooled tunable single-frequency pulsed slab laser. Background Technology

[0002] Single-frequency lasers have the advantages of narrow laser linewidth and long coherence length, and have been widely used in laser wind radar and atmospheric detection in recent years. To achieve spatial resolution, lidar often uses single-frequency pulsed lasers as the emission source.

[0003] To achieve long-range wind measurement, lidar atmospheric detection requires a high-energy single-frequency pulsed laser source, typically using a 1064nm fundamental frequency harmonic at 532nm. Assuming a wind speed of 100m / s, the Doppler frequency shift is only 0.354pm, corresponding to a frequency of only 376MHz. Generally, the emission wavelength of 532nm is locked to the edge of the iodine absorption line. The Doppler frequency shift is converted into a change in signal intensity. If a wind measurement accuracy of 0.6m / s is required, the frequency stability of the emission wavelength must be less than 1MHz, and the single-pulse energy often needs to be tens or even tens of millijoules. However, conventional solid-state lasers have very wide gain linewidths, often reaching tens of GHz without frequency control measures. The frequency also drifts due to environmental disturbances, also reaching tens of GHz, making them unsuitable for direct application in wind-measuring lidar.

[0004] Existing high-energy single-frequency pulsed laser systems commonly employ two schemes: First, continuous single-frequency seed lasers are used for fiber pulse modulation. Due to the often low duty cycle, the continuous seed laser power loss is significant, with the single-pulse energy modulated to only the nJ level. This requires multi-stage fiber pre-amplification before injection into the subsequent solid-state amplifier, making the laser system complex and costly. Second, a continuous single-frequency seed source is injected into a resonant cavity, while simultaneously detecting the resonance signal generated by the seed laser injection. Matching and locking between the cavity length and the frequency of the injected continuous seed laser are achieved using piezoelectric elements, electro-optics, or acousto-optic devices. After locking, Q-switching enables multi-pass amplification of the seed laser, suppressing quantum noise and achieving high-energy single-frequency pulsed laser output. However, the locking technology is often very complex and costly. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an air-cooled tunable single-frequency pulsed slab laser. Based on slab laser crystals, ring cavity technology, etalon filtering technology, and high-precision temperature control, it directly achieves high-energy single-frequency pulsed laser output.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A wind-cooled tunable single-frequency pulsed slab laser includes a diode array, a pump shaping system, a coupling cavity mirror, a slab laser crystal, a first reflecting mirror, and a thin-film polarizer, wherein...

[0008] The diode array serves as a pump source;

[0009] The pump shaping system is used to eliminate the slow-axis non-uniformity of the diode array, based on the direct partial end-face pumping of the slab laser crystal by the coupled cavity mirror;

[0010] The coupling cavity mirror, the first reflecting mirror, and the thin-film polarizer together form a ring resonant cavity. The oscillating laser passes through the slab laser crystal multiple times within the ring resonant cavity and is finally output as a single-frequency pulse laser via the thin-film polarizer.

[0011] The beneficial effects of this invention are as follows:

[0012] This invention achieves high pump power injection, eliminates thermally induced depolarization and thermally induced birefringence effects using a slab laser crystal, which is beneficial for high beam quality and high single-pulse energy output. The ring cavity overcomes the spatial hole burning effect, enabling single-frequency pulse laser output. Combined with high-precision temperature control, mode jump can be overcome. The etalon enables wavelength tuning without the need for continuous seed modulation or seed injection locking. The system is simple, reliable, and low-cost, and can be used as a high-energy single-frequency pulse laser source for atmospheric detection. It can also be used as an excellent single-frequency seed source for cascaded solid-state amplifiers to further enhance single-pulse energy. Attached Figure Description

[0013] Figure 1 This is a structural diagram of a wind-cooled tunable single-frequency pulse slab laser according to the present invention.

[0014] Figure label:

[0015] 1. Diode array; 2. Pump shaping system; 3. Coupled cavity mirror; 4. Slab laser crystal; 5. Slab Faraday rotator crystal; 6. Passively Q-switched crystal; 7. λ / 2 waveplate; 8. First mirror; 9. Thin-film polarizer; 10. Ereba; 11. Second mirror; 12. Third mirror. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0017] This invention provides an air-cooled tunable single-frequency pulsed slab laser, which directly achieves high single-pulse energy single-frequency pulsed laser output based on slab laser crystal, ring cavity technology, etalon filtering technology, and high-precision temperature control. The slab laser crystal employs partial end-face pumping, with the pump field distributed flat-top along the narrow length of the slab crystal, resulting in a one-dimensional temperature field distribution. This eliminates thermally induced depolarization and birefringence issues under high-power pumping. The ring cavity is a traveling-wave resonant cavity, overcoming mode competition caused by standing waves and greatly suppressing the spatial hole-burning effect, enabling single-frequency pulsed laser output. However, due to the relatively long cavity length and small longitudinal mode frequency interval, high-precision temperature control is used to overcome mode skipping issues. The etalon is a frequency-selective device that enables wavelength tuning. Based on the above design, high beam quality and high single-pulse energy direct output can be achieved without continuous seed modulation or seed injection locking, making it suitable as a high-energy single-frequency pulsed laser source for atmospheric detection.

[0018] Specifically, such as Figure 1 As shown, the diode array 1 has a rectangular light-emitting cross section. The pump shaping system 2 is used to eliminate the non-uniformity of the slow axis direction of the diode array 1. The slab laser crystal 4 is directly pumped from the end face based on the coupling cavity mirror 3. The temperature field inside the slab laser crystal 4 is one-dimensionally distributed. The laser is a multi-path folded structure. The oscillating laser passes through the slab laser crystal 4 multiple times, effectively increasing the resonant cavity length and cavity mode size. Since the thermal lensing effect only exists in the thickness direction of the slab laser crystal 4, the oscillating laser is an elliptical spot. The second reflector 11 and the third reflector 12 are placed at a small angle to eliminate parasitic oscillations in the resonant cavity under high-power pumping. The coupling cavity mirror 3, the first reflector 8, and the thin-film polarizer 9 together constitute the resonant cavity mirror. The resonant cavity is designed as a ring cavity to achieve single-frequency pulse laser output. The etalon 10 can achieve wavelength tuning. Combined with high-precision temperature control, mode jump can be overcome without continuous seed modulation or seed injection locking.

[0019] The laser has a multi-path folded structure, passing through the slab laser crystal 4 multiple times. Since the thermal lens exists only in the thickness direction of the slab, the cavity mode size of the resonant cavity in the orthogonal direction of the slab laser crystal 4 is inconsistent. The resonant cavity oscillating laser is an elliptical spot. The oscillating laser is output based on the thin film polarizer 9. However, since the thickness of the slab laser crystal 4 is only 1mm, the output laser is easily circularly symmetric based on cylindrical shaping and is a Gaussian mode, resulting in very high beam quality.

[0020] The diode array 1 is a vertical array that can be flexibly stacked according to the single-pulse energy output requirements. It can work in both pulse pumping and continuous pumping modes. The light-emitting cross section is rectangular. However, since the slow axis direction is the superposition of multiple single-tube light-emitting areas of diodes, the beam quality is poor and the pump distribution often appears serrated. The pump shaping system 2 is often based on the idea of ​​beam integration, such as rectangular waveguides or microlenses, to homogenize and shape the slow axis direction of the diode array 1, so that the long strip direction of the slab laser crystal 4 has a one-dimensional temperature field distribution, which is used to eliminate the problem of thermally induced birefringence of rod crystals under high-power pumping.

[0021] The coupling mirror 3 is used to couple pump energy and also serves as a folded mirror of the laser resonant cavity. Considering that spontaneous emission loss may occur during the energy storage stage under high-power pumping, the second mirror 11 and the third mirror 12 adopt a discrete structure with a gap between them. Spontaneous emission can leak through this gap without parasitic oscillation, thereby losing pump energy storage, reducing single-pulse energy output and system efficiency.

[0022] The slab laser crystal 4 can expand in width direction according to the single pulse energy output while keeping the thickness direction unchanged to achieve efficient heat dissipation. Two large heat dissipation surfaces are welded to the heat sink to achieve efficient and uniform heat dissipation. The laser oscillation back and forth transmission can almost fill the slab laser crystal, thereby efficiently extracting all the stored energy.

[0023] To ensure that the oscillating laser operates in only one direction to eliminate the spatial hole burning effect and achieve single-frequency pulses, the Faraday rotator crystal 5 is a slab structure. The polarization direction rotation of the polarized laser depends only on the direction of the applied magnetic field. Since the oscillating laser passes through the slab Faraday rotator crystal 5 multiple times, compared with a conventional Faraday rotator, this means that the applied magnetic field strength can be reduced by 1 / N, where N is the number of times the oscillating laser passes through, which is beneficial to the overall magnetic shielding design of the laser.

[0024] The slab Faraday rotator crystal 5, the λ / 2 waveplate 7, and the thin-film polarizer 9 together constitute an optical unidirectional diode, which allows the oscillating laser to propagate in only one direction along the ring cavity, eliminating the spatial hole burning effect caused by the standing wave cavity. By tuning the rotation angle of the λ / 2 waveplate 7, the p-polarization and s-polarization ratio can be flexibly realized. The s-polarization oscillates in the resonant cavity, and the p-polarization is output by the thin-film polarizer 9. No separate output cavity mirror is required. The effective output reflectivity can be flexibly adjusted according to the pump design and the single-pulse energy requirements. The Jones matrix is ​​often used for calculation. The equivalent reflectivity of the resonant cavity can be continuously tuned from 100% to 40%, which is sufficient to cope with conventional resonant cavity laser pulse output.

[0025] The passively Q-switched crystal 6 is used to generate Q-switched pulses. During the pumping and energy storage stage, the oscillating laser cannot oscillate back and forth. The slab laser crystal forms an effective population inversion number density storage. Once the oscillation threshold is reached, the passively Q-switched crystal 6 has high transmittance to the oscillating laser, which causes the laser to oscillate rapidly and form a pulse output.

[0026] The etalon 10 is inserted into the resonant cavity at a small angle. The coupling mirror 3, the first reflector 8, and the thin-film polarizer 9 together constitute the resonant cavity mirror. If the surface of the etalon 10 is parallel to the resonant cavity mirror, the etalon 10 will form a composite cavity with the original resonant cavity, and the resonant frequency in the cavity will change. Moreover, the relative jitter between the etalon 10 and the resonant cavity is extremely sensitive, and a stable single-frequency laser output cannot be obtained. The tilted placement of the etalon 10 can eliminate the coupling resonance between the end face and the resonant cavity mirror. The resonant frequency is no longer sensitive to the relative motion between the etalon 10 and the resonant cavity mirror. The etalon 10 only acts as a bandpass filter and selects from the many frequencies in the resonant cavity. In addition, in order to reduce insertion loss, the FP insertion position is generally selected at a position with a larger resonant cavity mode size.

[0027] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are 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 within the protection scope of the present invention.

Claims

1. A wind-cooled tunable single-frequency pulse slab laser, characterized in that, This includes a diode array, a pump-shaping system, a coupling cavity mirror, a slab laser crystal, a first reflecting mirror, and a thin-film polarizer, among which... The diode array serves as a pump source; The pump shaping system is used to eliminate the slow-axis non-uniformity of the diode array, based on the direct partial end-face pumping of the slab laser crystal by the coupled cavity mirror; The coupling cavity mirror, the first reflecting mirror, and the thin-film polarizer together form a ring resonant cavity. The oscillating laser passes through the slab laser crystal multiple times within the ring resonant cavity and is finally output as a single-frequency pulsed laser via the thin-film polarizer. A slab Faraday rotator crystal is connected to the rear end of the slab laser crystal. The slab Faraday rotator crystal has a slab structure. A second reflecting mirror and a third reflecting mirror are also arranged longitudinally at the rear end of the slab Faraday rotator crystal, with a gap between the second reflecting mirror and the third reflecting mirror. The front end of the thin-film polarizer is also provided with a standard etalon.

2. The air-cooled tunable single-frequency pulse slab laser according to claim 1, characterized in that, The cavity mode sizes of the resonant cavities in the orthogonal directions of the slab laser crystal are inconsistent, and the oscillating laser in the annular resonant cavity is an elliptical spot.

3. The air-cooled tunable single-frequency pulse slab laser according to claim 1, characterized in that, The diode array is a vertical array with a rectangular light-emitting cross-section.

4. The air-cooled tunable single-frequency pulse slab laser according to claim 1, characterized in that, The pump shaping system uses the idea of ​​beam integration to homogenize and shape the slow axis of the diode array, so that the long strip of the slab laser crystal has a one-dimensional temperature field distribution.

5. A wind-cooled tunable single-frequency pulse slab laser according to claim 1, characterized in that, The front end of the first reflector is also provided with a λ / 2 waveplate. The ratio of p-polarization and s-polarization is realized by tuning the rotation angle of the λ / 2 waveplate. The s-polarization oscillates in the ring resonant cavity, and the p-polarization is output by the thin film polarizer.

6. A wind-cooled tunable single-frequency pulse slab laser according to claim 5, characterized in that, The front end of the λ / 2 waveplate is also equipped with a passively Q-switched crystal to achieve narrow pulse width laser output.

7. A wind-cooled tunable single-frequency pulse slab laser according to claim 1, characterized in that, The standard etalon is inserted at an angle into the ring resonant cavity.

Images