Jiqiao Liu

Eye-safe, single-frequency pulsed all-fiber laser for Doppler wind lidar

A single-frequency pulsed erbium-doped fiber (EDF) laser with master-oscillator power-amplifier configuration at 1 533 nm is developed. A short-cavity, erbium-doped phosphate glass fiber laser is utilized as a seeder laser with a linewidth of 5 kHz and power of 40 mW. The seeder laser is modulated to be a pulse laser with a repetition rate of 10 kHz and pulse duration of 500 ns. The amplifier consists of two pre-amplifiers and one main amplifier. The detailed characteristics of the spectrum and linewidth of the amplifiers are presented. A pulse energy of 116 1J and a linewidth of 1.1 MHz are obtained. This laser can be a candidate transmitter for an all-fiber Doppler wind lidar in the boundary layer.

Eye-safe single-frequency single-mode polarized all-fiber pulsed laser with peak power of 361 W

An all-fiber, single-frequency, single-mode linearly polarized, high peak power pulsed laser at 1540 nm for coherent Doppler wind lidar is demonstrated. A narrow-linewidth seed laser is pulse modulated by an acousto-optic modulator and then amplified by two-stage cascade amplifiers. An 0.8 m long erbium/ytterbium co-doped polarization-maintaining fiber with a core diameter of 10 μm is used as the gain fiber of a power amplifier, and longitudinally varied strains are applied on the gain fiber to realize approximately 3.4 times enhancement of the stimulated Brillouin scattering threshold. Peak power of 361 W pulse width of 200 ns at 10 kHz repetition rate is achieved with transform-limited linewidth and diffraction-limited beam quality. To the best of our knowledge, it is the highest peak power of an eye-safe, single-mode narrow-linewidth pulsed fiber laser based on 10 μm core diameter silica fiber.

Frequency stabilization of a single-frequency all-solid-state laser for Doppler wind lidar

The master laser of an injection-seeded laser for Doppler wind lidar is frequency stabilized to a Fabry-Perot (FP) cavity using Pound-Drever-Hall technique. The FP cavity is specially designed to gain high temperature stability with Zerodur cavity and spacer. A computer based controller is used to sample and process the error signal. After the master laser is locked, the relative frequency drift is +-25 kHz in 1 s, and +-5 kHz in 1 h, which can satisfy the need of Doppler wind lidar.

All fiber pulsed coherent lidar development for wind profiles measurements in boundary layers

An all fiber pulsed coherent Doppler lidar (CDL) system at 1.54 ?m wavelength is developed for wind profiles measurements. This lidar affords 43.0-?J pulse energy at 10-kHz pulse repetition frequency with 500-ns pulse width. The lidar is operated in monostatic mode with 50-mm diameter telescope. The heterodyne mixing signals are acquired with 500 M/s analog to digital converter and 2048 points fast Fourier transform (FFT) is implemented. Line of sight wind speeds are measured with more than 3.0-km range in a horizontal direction and about 1.9 km in the vertical direction with 75-m range resolution. Systematic error of speed measurement of 0.2 m/s is validated.

Single frequency laser with long pulse for coherent lidar

An injection-seeded Nd:YAG laser with long pulse duration was designed and built. Single-frequency was achieved through ramp-fire technique. Long folded cavity and large pump spot was adopt to achieve long pulse duration and high energy. The laser operated at 200Hz. The pulse duration of about 80ns and pulse energy of 1mJ was achieved. The laser will be applied in a coherent Doppler wind lidar.

1540-nm single frequency single-mode pulsed all fiber laser for coherent Doppler lidar

A single-mode single frequency eye-safe pulsed all fiber laser based on master oscillator power amplification structure is presented. This laser is composed of a narrow linewidth distributed laser diode seed laser and two-stage cascade amplifiers. 0.8 m longitudinally gradient strained erbium/ytterbium co-doped polarization-maintaining fiber with a core diameter of 10 μm is used as the gain fiber and two acoustic-optics modulators are adopted to enhance pulse extinction ratio. A peak power of 160 W and a pulse width of 200 ns at 10 kHz repetition rate are achieved with transform-limited linewidth and diffraction-limited beam quality. This laser will be employed in a compact short range coherent Doppler wind lidar.

Single-frequency pulsed laser source with hybrid MOPA configuration

A unique approach with a hybrid master oscillator power amplifier configuration to obtain single-frequency, high-energy laser pulses at 1064 nm is presented. The setup consists of a single-frequency seed laser, a multistage fiber amplifier, and a four-pass crystal rod amplifier. Pulse energy of 10 mJ is obtained at the repetition rate of 100 Hz. The pulse width is about 110 ns with a transform-limited linewidth of 3.2 MHz. The M(2) factor of the output beam is about 1.5. To our knowledge, this is the first report of using a hybrid amplifier to obtain 10 mJ pulses with long pulse width and transform-limited linewidth.

Design and simulation of a biconic multipass absorption cell for the frequency stabilization of the reference seeder laser in IPDA lidar

The design process and simulation method of a multipass absorption cell used for the frequency stabilization of the reference seeder laser in integrated path differential absorption (IPDA) lidar are presented. On the basis of the fundamental theory of the Herriott multipass cell comprising two spherical mirrors, the initial parameters of the multipass cell, which has an optical path greater than 10 m and consists of two biconic mirrors, were calculated. More than 30 light spots were distributed on each mirror, and the distance between adjacent spots was mostly optimized to greater than six times the beam waist. After optimization, the simulated transmittance spectrum and associated differential signal were obtained. The interference induced by surface scattering was also simulated, and its influence on the differential signal was analyzed. A correspondence between the simulated results and the testing data was observed.

High energy single-frequency double-pulse hybrid MOPA system

A laser system capable of offering double single-frequency pulses based on a hybrid master oscillator power amplifier structure is presented. Combining the advantages of all-fiber amplifier, bulk-amplifier-chain of Nd:YVO4 and Nd:YAG, this novel design is capable of providing a pair of nanosecond laser pulses at 1064 nm wavelength with a temporal interval of 200 μs. Approximately 13 mJ of output pulse energy is recorded at a repetition rate of 30 Hz. The pulse width is around 20 ns and the spectrum linewidth is 34.1 MHz. The beam quality factor M 2 of output radiation is less than 1.30.

Development of All-fiber Coherent Doppler Lidar to Measure Atmosphere Wind Speed

An all-fiber pulsed coherent Doppler lidar (CDL) prototype is developed to measure wind profiles in the lower atmosphere layer. The all-fiber single frequency pulsed laser is operated with pulse energy of 50μJ, pulse width of 500ns and pulse repetition rate of 10kHz. The AOM heterodyne frequency is about 55MHz. The diameter of the telescope is 100mm. The heterodyne mixing signal is acquired with 500M/s AD card. Several experiments are implemented to validate the performance of the system. With 3000 pulses accumulated, the maximum horizontal measurement range of wind speed is about 4.2km in clear day, and the maximum vertical range is near 2km. The speed measurement accuracy of the lidar in hard target experiment is shown to be about 0.2m/s. An engineering prototype is being developed to measure wind speed in 5000m range, which will be used in the airport to measure atmosphere windshear.