Huaguo Zang

Single-frequency Q-switched double-pulse Nd:YAG laser

A laser diode dual-end-pumped injection-seeded single-frequency Q-switched double-pulse Nd:YAG laser is designed using a modified ramp-fire technique. The laser is capable of producing a pair of Q-switched single-frequency 1064 nm laser pulses in one pump period. Every pulse has an output energy of up to 10 mJ, width of nearly 20 ns, and interval of about 200 μs between two Q-switched pulses. The optical-to-optical efficiency of this laser is about 22.4% and its slope efficiency is 28%. A narrow spectrum linewidth of less than 28.6 MHz with a frequency of jitter around 1 MHz over 2 min may be obtained, and a beam quality of 1.23 in the horizontal direction and 1.31 in the vertical direction is detected.

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.

In-orbit operation of an atomic clock based on laser-cooled 87 Rb atoms

Atomic clocks based on laser-cooled atoms are widely used as primary frequency standards. Deploying such cold atom clocks (CACs) in space is foreseen to have many applications. Here we present tests of a CAC operating in space. In orbital microgravity, the atoms are cooled, trapped, launched, and finally detected after being interrogated by a microwave field using the Ramsey method. Perturbing influences from the orbital environment on the atoms such as varying magnetic fields and the passage of the spacecraft through Earth’s radiation belt are also controlled and mitigated. With appropriate parameters settings, closed-loop locking of the CAC is realized in orbit and an estimated short-term frequency stability close to 3.0 × 10−13τ−1/2 has been attained. The demonstration of the long-term operation of cold atom clock in orbit opens possibility on the applications of space-based cold atom sensors.Cold atom clocks are among the most precise measuring devices and play key roles in everyday life and scientific explorations. Here the authors demonstrate the first in-orbit atomic clock using cold Rb atoms operating in microgravity and opening possibilities of space surveys and tests of fundamental physics.

Development of a coherent Doppler lidar to measure atmosphere windshear

A pulsed coherent Doppler lidar prototype at wavelength of 1064nm was developed to measure windshear in the lower troposphere layer. The laser transmitter was an injection-seeded pulsed Nd:YAG laser with pulse energy of 0.5mJ, pulse duration of 80ns and pulse repetion rate of 200Hz. Hard-target speed calibration expriments were carried out to demonstrate speed measurement accuracy of 0.23m/s for the lidar. Then line-of sight atmosphre wind velocity measurement in 500m range with 40m range resolution was implemented. The lidar is being optimized to measure windshear at 2km range away.

Double-pulse single-longitudinal-mode operation of injection-seeded laser using intracavity phase modulator

A single-longitudinal-mode (SLM) double-pulse injection-seeded neodymium-doped yttrium aluminium garnet (Nd:YAG) laser was established utilizing an RbTiOPO4 electro-optic crystal to modulate the optical path of the slave resonator for generating a resonance condition. The Q-switcher was fired twice during every pump period. This enabled the laser to emit a pair of SLM laser pulses with a time separation of 200 mu s. Each pulse had a pulse energy of 13 mJ at 50-Hz repetition rate, pulse duration of 20 +/- 0.5 ns, and linewidth of 30 +/- 0.3 MHz (within 2 min). The beam quality factor of M-2 was <1.22. A frequency jitter of 1.4 MHz was obtained within 2 min

Comparison of high repetition rate Q-switched 355nm ultraviolet lasers with EOM and AOM

Two kinds of Q-switched ultraviolet lasers using an acousto-optic modulator and an electro-optic modulator in the same cavity structure are demonstrated, with type I phase-matched LBO as second harmonic generation crystal and type II phase-matched LBO as third harmonic generation crystal. For acousto-optic Q-switched UV laser，a maximum average power of 6.3W with the shortest pulse width of 12 ns was obtained at the repetition rate of 22 kHz when the pump power reached 52.4 W. The optical conversion efficiency was up to 12%. Then we used a La3Ga5SiO14 crystal electro-optic modulator to replace the acousto-optic modulator. The 1.29W output power at 355nm wavelength was obtained at the repetition rate of 10 kHz when the pump power was increased to 20.4W, and the UV laser pulse width was as short as 9.6ns.The optical conversion efficiency was up to 6.3%.

Conductively cooled 1-kHz single-frequency Nd:YAG laser for remote sensing

A conductively cooled, laser diode (LD) end pumped, injection-seeded single frequency Nd:YAG laser is designed and implemented. A compact standing wave resonator with dual-end-pumping arrangement is constructed, and two fiber-coupled LDs with maximum output power of 150 W independently are used as the pump source. A composite Nd:YAG rod is utilized as the gain medium with the aim of reducing thermal lens. The optimized ramp-fire technique is applied to build reliable single longitudinal mode oscillating. The laser is capable of producing a 10 mJ Q-switched pulse at the pulse repetition rate of 100 Hz and 250 Hz. Due to the thermal effect in YAG rod, although the single frequency is remained at 1000 Hz, the single pulse energy is decreased to 8.8 mJ. The M2 of the laser beam are no more than 1.3 for all three operation frequency. At 1000 Hz with the output of 8 mJ, the linewidth of 54.2 MHz and the frequency jitter of less than 3.5 MHz (rms) over 2 min are detected by heterodyne technique.

Laser Doppler Vibrometer for detection of sound wave

For the communication from the aerial platform with the autonomous underwater vehicles, a laser Doppler vibrometer is under developing. The detection of the laser Doppler shift of the sea surface vibrating is implemented. The sound-pressure level of 150.8 dB is obtained under the acoustic signal of 7 kHz.