[Show abstract][Hide abstract] ABSTRACT: Active coherent beam combination has been a hot area of research for several years. Particular algorithm module is used to stabilize the phase difference between beamlets, and make them coherent. The phase noise increases with the raising power of laser output. Under low power condition, we simulate the phase noise of high power laser amplifier by the Arbitrary Function Generators (AFGs), and send them to the phase modulators to destabilize the phase, to test the performance of the phase lock algorithm. The experimental results show the feasibility.
No preview · Article · Jan 2015 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: A phase controller for coherent beam combining (CBC) of fibre lasers has been designed and manufactured based on a stochastic parallel gradient descent (SPGD) algorithm and a field programmable gate array (FPGA). The theoretical analysis shows that the iteration rate is higher than 1.9 MHz, and the average compensation bandwidth of CBC for 5 or 20 channels is 50 kHz or 12.5 kHz, respectively. The tests show that the phase controller ensures reliable phase locking of lasers: When the phases of five lasers are locked by the improved control strategy with a variable gain, the energy encircled in the target is increased by 23 times than that in the single output, the phase control accuracy is better than λ/20, and the combining efficiency is 92%.
No preview · Article · Apr 2014 · Quantum Electronics
[Show abstract][Hide abstract] ABSTRACT: A near infrared tunable liquid crystal birefringent filter is developed by cascading a series of optical elements including the wide range wire-grid polarizers, the nematic liquid crystal retarders and the quartz retarders. The center wavelength of the filter's bandpass could be randomly selected or scanned in the designed spectral range with almost exactly the same out-of-band suppression by harmoniously adjusting the driving signals. The tuning range of the filter is 900nm∼1700m, the clear aperture is over 50mm, and the bandwidth FWHM is about [email protected]
/* */ filter provides more flexible functions such as random wavelength selection and arbitrary spectral scanning step. Due to the excellent imaging quality and the relatively wide angle-of-acceptance with a large aperture, the filter enable snapshot spectral imaging sensors and compact systems without any moving parts, which is of great use in a wide variety of applications such as remote sensing for environmental monitoring, agriculture census, and mineral resources detection.
No preview · Article · Jan 2014 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: A coherent combination model of fiber lasers has been established. The relative beam quality factor has been introduced and studied as a proper beam quality factor for the combined coherent beam. The disturbance of the phase shift, polarization degradation, distribution characteristic, the wave-front aberration and the tilt error has been numerically studied to investigate their effects on the beam quality. This model has been also used to analyze the control of beam steering. The results have shown that the impact of the phase shift on the combination is more serious than that caused by polarization degradation, and the coherence degradation caused by the phase grating is more severe than that caused by the phase shifter.
[Show abstract][Hide abstract] ABSTRACT: Liquid crystal optical elements have important applications in laser facility, and the indium tin oxide (ITO) films are generally used in liquid crystal optical elements as transparent conductive electrodes. Laser induced damage of ITO films leads to failure of liquid crystal optical elements. The laser damage model of ITO films which simulates the temperature distribution and thermal stress distribution was established. The laser damage of ITO films was experimented through pump-probe technology, and the power density producing damage at a probability of 50% (i.e., damage threshold) was obtained by 1-on-1 testing, and the square resistance of the film after laser irradiation was also measured. The experimental data basically agree with the simulated results. The results show that 1064 nm laser damage of ITO film occurs mainly by thermal stress. The damage of ITO film begins from K9 glass substrate after CW laser irradiation, while the damage begins from the surface of ITO film after pulsed laser irradiation. Furthermore, the laser damage thresholds decrease with the increase of thickness of ITO films. The square resistance of ITO films increases with the increase of laser intensity unless the ITO films have been damaged completely. The optimal thickness of ITO film in liquid crystal optical element depends on the factors of laser damage, transparence and square resistance.
No preview · Article · Feb 2012 · Gaoya Wuli Xuebao/Chinese Journal of High Pressure Physics
[Show abstract][Hide abstract] ABSTRACT: In order to evaluate the of coherent combination for fiber lasers, a Gaussian beam combination model of large array was established. Firstly, the coupled wave theory was used to study the effects of disturbances of phase shift, depolarization and bandwidth on the coherent beams. Then, the atmospheric transmission model was used to analyze the impact of the turbulence on the beam transmission efficiency and quality in the actual beam propagation. The results show that the de-coherence caused by phase shift can decrease the Strehl ratio to 1/N, but the Strehl ratio of depolarization is reduced to 0.5. Furthermore, the atmospheric turbulence caused by fluctuation of the refractive index will disturb the amplitude and phase of the laser beam, and broaden the beam on the basis of diffraction. It concludes that the phase shift is more serious than the depolarization in coherent combination and the atmospheric turbulence could cause the expansion and de-coherence of the beam.
No preview · Article · Jul 2011 · Guangxue Jingmi Gongcheng/Optics and Precision Engineering
[Show abstract][Hide abstract] ABSTRACT: A polarization-independent phase-only Liquid Crystal (LC) phase retarder was demonstrated by using two orthogonal identical Liquid Crystal Variable Retarders (LCVR). Based on Jones matrix theory, the relationship of polarization state between input beam and output beam was deduced. And the Stokes parameters were measured on the condition that the voltage individually applied to the two LCVRs was 1.55 V and 1.49 V. It is proved that the structure well operates in polarization-independent modulation. And the phase variation induced by voltage from 1~2.7 V is given out.
No preview · Article · Dec 2010 · Guangdian Gongcheng/Opto-Electronic Engineering
[Show abstract][Hide abstract] ABSTRACT: In a laser coherent combination, the phase detection and control is the most critical. Using the beat frequency method, consistence
of the phase in output beams can be ensured through real-time detection and correction for the phase change. Phase noises
are controlled by a liquid crystal phase modulator. At the same time, the liquid crystal polarization controller is used to
make the polarization state stable, which is good for the improvement of the combining efficiency. The wave length of the
main oscillation laser is 532nm. The output power of laser can be adjusted continuously from 0 to 6W. The shifted frequency
of the system is 40MHz. The accuracy for phase control is superior to λ/70RMS. In the process of closed-loop control, using the liquid crystal phase and polarization controller, a better signal
phase correction of optical path has been achieved for the coherent combination of high power laser arrays.
No preview · Article · Nov 2010 · Applied Physics B
[Show abstract][Hide abstract] ABSTRACT: The possibility of liquid crystal used in optical isolator is discussed based on the selective reflection of cholesteric liquid crystal. From theoretical analysis and experimental result, it is clear that the liquid crystal optical isolator has a good isolation degree (isolation is 13 dB). and an excellent transmission (insertion loss is 1 dB). So the liquid crystal optical isolator has an important application value in the fabrication of large caliber optical isolator.
No preview · Article · Apr 2008 · Guangdianzi Jiguang/Journal of Optoelectronics Laser
[Show abstract][Hide abstract] ABSTRACT: Multi-walled carbon nanotubes water-surfactant suspensions were prepared by ultrasonication, and the optical limiting curves were measured for 1064 nm, 10 ns Nd:YAG Q-switched pulsed laser. The experimental results indicated that the output energy varied linearly with input fluences at a lower level, when the incident fluences increase to about 160 mJ/cm2, the output was clamped and tended to the value 16 mJ finally, and the transmittance of the sample decreased from 71% to 15%. In addition, the optical limiting mechanisms were investigated through performing Z-scan, pump-probe and 45° scattering experiments. The results show that the nonlinear scattering dominates the transmittance losses and the nonlinear refraction is secondary.
No preview · Article · Jun 2006 · Qiangjiguang Yu Lizishu/High Power Laser and Particle Beams