Xinghua Lu

Theoretical and experimental research on cryogenic Yb:YAG regenerative amplifier

Based on the theory of quasi-three-level rate equations modified by amplified spontaneous emission, the stored energy density and the small signal gain of the cryogenic Yb:YAG regenerative amplifier for a given geometry for pulsed pumping in three dimensions are theoretically studied using the Monte Carlo simulation. The present model provides a straightforward procedure to design the Yb:YAG parameters and the optical coupling system for optimization when running at cryogenic temperature. A fiber-coupled laser diode end-pumped cryogenic Yb:YAG regenerative amplifier running at 1 030 nm is demonstrated with a maximum output energy 10.2 mJ at a repetition rate of 10 Hz. A very good agreement between the experiments and the theoretical model is achieved.

A highly stable laser diode pumped cryogenic Yb:YAG nanosecond regenerative amplifier

A diode-pumped cryogenic-cooled nanosecond Yb:YAG regenerative amplifier based on the disk concept has been developed and used in a joule-class MOPA laser system. The output pulse energy is more than 11xa0mJ at a 10xa0Hz repetition rate at 163xa0K. An excellent energy stability of 1.8% fluctuations is achieved.

Real-time characterization of FM-AM modulation in a high-power laser facility using an RF-photonics system and a denoising algorithm

FM-AM modulation of high-power lasers significantly affects laser performance. Therefore, precise measurement of the FM-AM modulation depth is necessary. The subsequent FM-AM modulation generated by group velocity dispersion when the laser pulse propagates through a fiber affects the measurement accuracy. In order to eliminate this effect, a waveform-acquisition module is proposed that converts a broad-spectrum pulse of 1053 nm to a narrow-spectrum pulse of 1550 nm, without affecting the waveform. In addition, a signal-processing algorithm based on the orthogonal matching pursuit method is implemented to remove the sampling noise from the waveform. In this way, the signal-to-noise ratio of the measurement can be readily improved. Both theoretical and experimental results indicate that the proposed FM-AM modulation detection system is effective and economical. It can measure the FM-AM modulation depth precisely, and therefore shows considerable promise for future applications in high-power lasers.

Sapphire face cooling for high-repetition-rate terawatt-class Ti:sapphire amplifier

In this work, we evaluated the feasibility of sapphire conductive cooling for short-pulse Ti:Sapphire (Ti:sa) laser amplifiers which suffers from thermal issues under high-repetition-rate and high-energy operation. Numerical heat transfer simulations of 100-TW class sapphire face-cooled Ti:sa gain modules operated around 300 W average powers are presented. The distributions of temperature, stress, strain, and birefringence in liquid cooled sapphire/Ti:sa/sapphire assembly are calculated by a finite element analysis. Based on these data, the thermal induced wave front distortions and depolarization are investigated for different repetition rates. We determine that sapphire face cooling concept holds a promise of achieving higher energies and repetition-rates in Ti:Sa amplifiers.

Research and control of thermal effect in a helium gas-cooled multislab Nd:glass laser amplifier

As the development of the laser-driven technology, the next generation of laser-driven device sets higher requirement for the repetition frequency. The higher repetition gives rise to thermal deposition, which induces thermo-optical effect, elasto-optical effect and bulk displacement. The thermal efficient management is an important approach to dissolve the thermal deposition. The quasi uniform distribution of heat medium is realized by helium cooling Nd:glass slab and the control of edge temperature. In the case, wavefront distortion and depolarization losses is obtained in experiment. Results said that both of them are improved greatly. At the same time, the distribution of temperature, stress and strain and stress birefringence in Nd:glass are analyzed by using finite element numerical simulation method. And the calculation results show that the wavefront distortion and depolarization losses match with the experimental results very well.

High energy quadruple pass amplifier for high power laser preamplifier module

Pre-amplifier between the frontend and main power amplifier is the key unit of high power laser divers. The recent progresses on the off-axis quadruple pass amplifier are presented, which include the beam path design, parasitic oscillation research and experimental results. A single longitudinal mode, temporally shaped laser pulse with 5ns pulse duration at 1053nm is injected into a Nd: Glass regenerative amplifier, which can provide a 12mJ energy output with 0.5% long term energy stability. The quadruple pass amplifier is designed as an off-axis pattern. With 1.3mJ energy injection, amplified pulse with 16.5J can be achieved, and the measured output energy stability of the amplifier is 7.3% (PV) at this output energy level, corresponding to a 21 shot result. The total gain of the amplifier is more than 10,000. The parasitic oscillation was analyzed and discussed, and the parasitic mode and pencil beam are neither observed in the experiment.

Transient thermal effects in end-pumped cryogenic Yb:YAG regenerative amplifier

The three-dimensional heat deposition of the cryogenic Yb:YAG regenerative amplifier, which is yielded by pulsed pumped laser, is derived in details based on the theory of quasi-three-level rate equations. Furthermore, the transient temperature field, stress, and strain induced by the thermal gradients in the laser crystal are analyzed by use of the finite element method. Then the thermally induced lens and depolarization in the cryogenic regenerative amplifier are theoretically studied. We find that for the pump and cooling structure which has been designed, the focal length of the thermally induced lens is about 15u2009m and the depolarization rate could be ignored. The maximum output energy 10.2u2009mJ at a repetition rate of 10u2009Hz with nearly TEM00 mode profile is obtained using the designed pump and cooling structure.

LD pumped cryogenic-cooled Yb:YAG disk regenerative amplif ier

A diode-pumped cryogenic-cooled Yb:YAG regenerative amplifier based on the thin disk concept, producing 14.2-mJ, 10-ns pulses with optical-to-optical conversion efficiency of ~7% at a repetition rate of 10 Hz at 163 K, is presented.

High precision synchronization of shaped nanosecond pulse with compressible chirped short pulse used in front-end of ICF

A method for electrical waveform generation based on chirped pulse stacker in intensity modulation pulse shaping is provided as a means for high precision synchronization between nanosecond shaped pulse and compressible chirped short pulse in inertial confinement fusion (ICF) research. The arbitrary shaped optical pulse could be obtained, and the measured synchronization precision between ultra-short pulse and shaped optical pulse with the same or different wavelengths is better than 2.75 ps root mean square error.