We demonstrate a wavelength tunable continuous wave single-frequency Cr:ZnSe laser based on a self-seeded ring cavity configuration in this paper. The laser system is based on anti-coated Cr:ZnSe crystal which has a length of 6 mm and a low signal transmission of 15% (at 1908nm). Unidirectional operation of Cr:ZnSe laser is obtained by using a retro-reflecting device which can retro reflect a self-seed laser back into the ring cavity. The transmission of the output coupler is also optimized to get unidirectional operation. With three different birefringent filters inserting in the cavity, single-frequency operation with narrow linewidth is obtained. By rotating the angle of the birefringent filters, the laser’s wavelength under single-frequency operation could be continuously tuned from 2338 nm to 2572 nm. The tuning range is over 200 nm. The maximum single-frequency output power is 0.92 W at wavelength of 2357 nm.
Long-range wind sensing using coherent Doppler lidar is attractive in many fields such as wind shear warning, aerosol detection and aircraft wake vortex detection. Recently, single frequency, all-solid-state laser around 1.6 μm has caused great interests for its eye-safety and high pulse energy. Velocity accuracy which is one of the key factors of wind lidar systems needs to be calibrated. The 1645 nm eye-safe coherent Doppler wind lidar based on injection-seeded technique consists of laser systems, transceiver optics, and data processing systems is developed. The average power of the laser pulses is 2.6 W with a pulse width of 190 ns at a repetition rate of 300 Hz. The accuracy of velocity measured by the lidar system is calibrated with a velocity calibrator based on a servo motor with a maximum speed of 3000 r/min and a rotating disk with a diameter of 300 mm. A real-time display software based on the LabVIEW platform is designed to get the velocity results and signal to noise ratio (SNR) from the FPGA acquisition module, and the central frequency correction algorithm is used to eliminate frequency jitter of the laser. To calibrate the wind velocity near 0 m/s, a nonmoving hard target at the range of 1.2 km with an elevation angle of about 0.5 deg is measured. Results show that a velocity accuracy (standard deviation of the measurement errors) of 0.38 m/s in the range ±40 m/s and the accuracy of zero velocity is 0.16 m/s.
A1645nm injection-seeded Q-switched Er:YAG ceramic laser pumped by a 1532 nm fiber laser with changeable pulse repetition frequency (PRF) used for Coherent wind measurement Lidar is demonstrated. Single-frequency operation of Er:YAG laser is achieved by injection seeding technique. A ‘M-shape’ ring cavity is utilized to eliminate the effects of spatial hole burning. The laser delivered single-frequency pulses with energy ranging from 6.6 to 10.2 mJ. The corresponding pulse width and PRF varied between 179 ns-271 ns and 300 Hz-1 kHz, respectively. And the line width at 300 Hz is measured to be 2.82 MHz. The measured M2 factors are 1.51 and 1.54 in x and y directions, respectively.
A single-frequency injection-seeded Er:YAG ceramic laser with a pulse repetition frequency (PRF) running at 1645 nm is demonstrated. The Er:YAG ceramic laser is seeded with a Er:YAG non-planar ring oscillator (NPRO) laser. Pulse energy of 5.19 mJ, pulse width of 571 ns at a PRF of 1 kHz is obtained. The fluctuation of the average power is measured to be less than 1.1% in 30 min. The M2 factors are 1.23 and 1.39 in x and y directions, respectively.
A 1645-nm injection-seeded Q-switched Er:YAG master oscillator and power amplifier system is reported. The master oscillator generates single-frequency pulse energy of 11.10 mJ with a pulse width of 188.8 ns at 200 Hz. An Er:YAG monolithic nonplanar ring oscillator is employed as a seed laser. The output pulse from the master oscillator is amplified to 14.33-mJ pulse energy through an Er:YAG amplifier, with a pulse width of 183.3 ns. The M2-factors behind the amplifier are 1.14 and 1.23 in x- and y-directions, respectively. The full width at half maximum of the fast Fourier transformation spectrum of the heterodyne beating signal is 2.84 MHz.
An Er:YAG triangular ring laser resonantly pumped by a 1470 nm laser diode was reported. 7.28 W continuous-wave output power at 1645 nm was obtained by using a triangular ring resonator. In the Q-switched mode, the Er:YAG laser generated pulse energies from 6.05 mJ to 16.6 mJ at 1645 nm when pulse repetition rates change from 1 kHz to 200 Hz. By inserting an etalon into the resonator, the Er:YAG laser yielded Q-switched energies from 1.714 mJ to 5.1 mJ at 1617 nm when pulse repetition rates change from 1 kHz to 200 Hz.
A new method for combining Finite Element Method (FEM) thermal analysis and thermo-mechanical coupling method for calculating the thermal lensing values in diode end-pumped Er:YAG lasers is proposed. A finite-element model is used to simulate the thermal effects in different Er:YAG crystals with pumping scenarios. The influences of pump powers, crystal absorption coefficients and crystal sizes on the Er:YAG thermal effects are discussed, and the relationship between the thermal effects and thermal lensing effects is analysed. A thermo-mechanical coupling model is also constituted for finite-element analysis based on the above results, and the focal length of the Er:YAG crystal with different pump powers are obtained by using this thermo-mechanical coupling model. The predicted thermal lensing values are compared with experimental results, which agree well with the simulated results.
Coherent Doppler wind lidars (CDWL) are widely used in aerospace, atmospheric monitoring and other fields. The parameters of laser source such as the wavelength, pulse energy, pulse duration and pulse repetition rate (PRR) have significant influences on the detection performance of wind lidar. We established a simulation model which takes into account the effects of atmospheric transmission, backscatter, atmospheric turbulence and parameters of laser source. The maximum detection range is also calculated under the condition that the velocity estimation accuracy is 0.1 m/s by using this model. We analyzed the differences of the detection performance between two operation systems, which show the high pulse energy-low pulse repetition rate (HPE-LPRR) and low pulse energy-high repetition rate (LPE-HPRR), respectively. We proved our simulation model reliable by using the parameters of two commercial lidar products. This research has important theoretical and practical values for the design of eye-safe coherent Doppler wind lidar.