SBS Phase Conjugation Research Articles

Rotating off-centered lens in SBS phase conjugation mirror for high-repetition-rate operation.

A new method using a rotating off-centered lens is proposed to reduce the heat accumulation at the focal spot of a stimulated Brillouin scattering phase conjugation mirror at high-repetition-rate operation. Theoretical simulation of the beam intensity pattern at the focal point indicates there is less coma-aberration using a rotating off-centered focusing lens than with a rotating wedge and a conventional lens. The resultant SBS output parameters using this new method are substantially improved comparable to those of a non-rotating conventional method for high-repetition-rate operation, while the former operates quite well for higher power and the latter operates only for lower input power. High reflected energy and a good beam pattern are demonstrated using the proposed method in the present experimental conditions of 50 mJ at 1 kHz.

High repetition rate and high beam quality joule level Nd: YAG nanosecond laser for Thomson scattering diagnosis

A joule-level Nd: YAG nanosecond laser of high repetition frequency and high beam quality is developed for Thomson scattering diagnosis. The laser is designed as a master oscillator power-amplifier system mainly including single longitudinal mode seed, pre-amplifier unit and energy extraction unit. The single-longitudinal-mode Q-switched laser of a high stability is taken as the seed laser of output pulse at J level. The pre-amplifier unit amplifies the J-level pulse laser beam into hundreds of mJ level. In order to obtain the high-quality laser beam output, phase conjugation is adopted to compensate for the laser beam distortion. The ultra-filtered FC-770 is taken as an SBS gain medium of 0.0011 cm-1 absorption coefficient, 197.9 GW/cm2 optical breakdown threshold and 3.5 cm/GW gain coefficient. The double-pass amplification of SBS phase conjugation could realize a real-time repair towards the non-uniformity, deformation and wavefront aberration caused by thermal distortion of the optical components and the laser amplifier to achieve the uniform amplified beam output of high quality close to the diffraction limit. In the energy extraction unit, the amplifier of large-diameter slab is used for energy amplification. The size of the slab is 7 mm 35 mm138.2 mm of 56 cutting angle and 0.6% Nd3+ doping concentration. The slab is plated by a layer of SiO2 against light leak. Horizontal pumping mode is adopted. And the slow axis of the laser diode is almost the same as the length of the slat and the direction of laser transmission. The single-plane array is composed of 8 groups of vertical stacks and each group consists of 12 laser diode bars of power 200 W. At 200 Hz repetition frequency, 250 s pump pulse width and 140 A pump current, the up to 2.3 J stored energy can be achieved The energy extraction unit achieves high gain amplification and finally outputs high-quality laser beam. Under the condition of 200 Hz high repetition frequency and 8.23 J single pulse energy injected by the single longitudinal mode seed, 1.85 J output energy is gained. The energy extract efficiency of the laser system is 52.46%. The output laser possesses a pulse width of 5.36 ns, a far field beam spot 1.72 times the diffraction-limited value, and 1.3% energy stability (RMS).

带SBS相位共轭镜的高重复频率高功率激光系统研究进展

带SBS相位共轭镜的高重复频率高功率激光系统研究进展

Laser Tracking and Pointing at a Target with StimulatedBrillouin Scattering

Laser tracking and pointing at a simulated movingtarget in atmosphere 1.27 km away is realized experimentally, in whichstimulated Brillouin scattering (SBS) phase conjugation technology andvelocity compensation mirror are used. Only if the angle between theSBS phase conjugation laser and the illumination laser is smaller thanthe atmosphere isoplanatic angle ψ0, is the wave-front aberration oflaser beam produced by atmospheric turbulence compensated for inreal time. This experiment was carried out with horizontal ranges1.27 km at 50 m height above the ground, and Nd:YAG lasers are used. Bychanging the angle of a velocity compensation mirror reflecting the SBSphase conjugation laser to the simulated target, simulated targets withdifferent moving velocities are tracked and pointed by the laser beam.The spot and energy distribution of illumination laser spot and SBSphase conjugation laser are recorded. The energy back to target is upto 75 mJ. The SBS phase conjugation laser spot shows that it is focusedat the simulated moving target within a small area.

Polarization Characteristics of Fiber-Optic SBS Phase Conjugation

Polarization characteristics of a SBS phase conjugation in multimode fibers with different core sizes and fiber lengths are investigated experimentally. A degree of polarization (DOP) of the Stokes wave becomes better as a fiber becomes shorter and is recovered more than 95% in 0.5 m fibers with different core size. The averaged DOP keeps more than 90% even in fibers with 200 m length. A direction of a linear polarization of the SBS phase conjugation coincides with that of an incident light, independent of the fiber length and thickness.

Diffraction limited output from a CW Nd:YAG master oscillator/power amplifier with fibre phase conjugate SBS mirror

A CW Nd:YAG master oscillator power amplifier with fibre based SBS phase conjugate mirror is reported. A four-pass amplifier configuration is employed to compensate pump induced thermal lens and birefringence in the amplifier rod in conjunction with a fibre phase conjugator to achieve diffraction limited output beam quality. Maximal attainable gain of ∼1.9 for the system is obtained. Application of the technique to diode pumped systems for high gain and high power delivery is proposed.

PHASE CONJUGATED LASERS APPLIED TO X-RAY GENERATION

Three laser systems that are being developed for use in X-ray generation which incorporate SBS phase conjugate mirrors are described. A 25 J/pulse Nd:glass laser is being developed for commercial proximity print X-ray lithography; a 0.5 J/pulse, 1.3 kHz pulse repetition frequency laser is being built for soft X-ray projection lithography; and a 1 kJ/pulse laser driver for a table top X-ray laser has been designed. The results of prototypical experimental investigations are presented and the basic design principles for high average power phase conjugated laser systems shared by each of these lasers are discussed.

A PHASE CONJUGATE Nd:YAG LASER WITH BEAM STEERING

We analyse the competitive effects which alter the stability of SBS phase conjugate mirrors when the laser operates at repetition rates between 10 and 30 Hz. Satisfactory results are obtained with nitrogen gas cell at 180 Atm. We also propose and experimentally demonstrate a SBS phase-conjugate Nd:YAG laser source with a beam steering function. The laser, designed as an oscillator-amplifier configuration, incorporates a TeO 2 acousto-optic deflector on the low energy beam. The high energy beam (100–185 mJ) is thus deflected over 2.7° and 40 resolved beam directions are obtained with 5 µs access time.

PHASE CONJUGATION OF KrF LASER RADIATION

We repor t observat ions of phase conjugate r e f l e c t i o n of KrF l a s e r r a d i a t i o n using both degenerate four-wave mixing (DFWM) and s t imulated B r i l l o u i n s c a t t e r i n g (SBS). Using DFWM we have measured r e f l e c t i v i t i e s of .L 300% and the r e s u l t s a r e i n good agreement with a theory f o r a thermal ly induced mechanism i n the medium. The SBS phase conjugate mirror has been used i n a v a r i e t y of app l i ca t ions which a r e of i n t e r e s t t o t h e development of high energy rare-gas ha l ide l a s e r s .