It’s widely agreed that optical characteristics at crystal boundary may change comparing to the internal part of bulk crystal but, as far as we know, sometimes the phenomenon, for example, the variation of susceptibility usually can’t be intuitively, simply presented in experiments. Recently, we observe a kind of special harmonic generation which is at the same wavelength as incident light. Besides, this kind of harmonic generation behaves in a similar way with nonlinear Cherenkov radiation, thus we call it linear Cherenkov radiation (LCR). We theoretically predict and calculate the phase-matching scheme and radiation path of LCR. In our experiment, we employ a polished KDP to verify our theory about the conversion of polarization in this process, and the phenomenon also help to rule out the possibility of birefringence at boundary. Combining with the coupling wave equation, we can derive new elements in linear susceptibility tensor according to the polarization states of incident light and LCR. The result tells us the linear susceptibility at the KDP boundary is assuredly different from that in bulk crystal, and this is mainly because of the breakdown of crystal symmetry at boundary, in our opinion. The existence of LCR is evidence of the variation of linear susceptibility. And in return, we could use this phenomenon to probe the non-zero elements in the tensor.
Advanced an online low 1ω drive irradiance tuning technique of frequency conversion crystals of high power solid-state laser facility, which can acquire the best match angle of frequency conversion crystals through online low 1ω drive irradiance tuning curve test, and achieve fast and high precision angle correction to assure the frequency conversion crystals to achieve the highest energy conversion efficiency in shot experiments. Analyzed the possibility of online low 1ω drive irradiance tuning technique of frequency conversion crystals, researched the technical scheme of online low 1ω drive irradiance tuning of frequency conversion crystals, and applied this technique on SG facility, which achieved 60%~70% frequency conversion efficiency in high energy shots.
The high power solid laser system is becoming larger and higher energy that requires the beam automatic alignment faster and higher precision to ensure safety running of laser system and increase the shooting success rate. This paper take SGIII laser facility for instance, introduce the basic principle of automatic alignment of large laser system. The automatic alignment based on digital image processing technology which use the imaging of seven-classes spatial filter pinholes for feedback to working. Practical application indicates that automatic alignment system of cavity mirror in SGIII facility can finish the work in 210 seconds of four bundles and will not exceed 270 seconds of all six bundles. The alignment precision promoted to 2.5% aperture from 8% aperture. The automatic alignment makes it possible for fast and safety running of lager laser system.
To assure that the frequency conversion crystals of SG facility are always being in the
best shot position, and have the highest energy conversion efficiency with various beam conducting
directions, we researched the precise tuning technique of frequency conversion crystals with the SG
facility. The on-line quick tuning method of target point detecting with preshot was used in precise
tuning of crystal match angle, and helped to correct the off-line match angle satisfactorily. With
crystal alignment technique and crystal accompany technique, the precise tuning of crystal match
angle can assure the crystals to maintain a stable high efficiency in a long experiment period.
Experiment of entire beam wavefront compensation was carried out in a beamline of a high power laser facility, and two adaptive optics systems with different intentions were applied in the chosen beamline. After correction, the far-filed irradiance distribution is concentrated evidently and the entrance rate of 3ω focal spot to a 500-μm hole is improved to be about 95% under number kilojoules energy.
Beam alignment of multi-pass amplification is based on cavity mirror alignment. To optimize multi-segmental parallel cavity mirror alignment arithmetic of high power solid-state lasers, propose a new type of arithmetic of multi-pass beam path cavity mirror based on diffraction symmetry, and the accuracy of multi-pass amplification beam path alignment is improved by 10μrad up to 3.96μrad. The arithmetic avoids low accuracy of CM alignment caused by poor image quality, It makes SG-Ⅲ facility operate long term and properly.
SG-III laser facility is now the largest under-construction laser driver for
inertial confinement fusion (ICF) research in China, whose 48 beams will deliver 180kJ/3ns/3ω energy to target in one shot. Till the summer of 2014, 4 bundle of lasers
have finished their engineering installation and testing, and the A1 laser testing is
undergoing. A round of physics experiment is planned in Oct. 2014 with 5 bundle of
lasers, which means the facility must be prepared for a near-full-capability operation
before the last quarter of 2014. This paper will briefly introduce the latest progress of
the engineering and research progress of SG-III laser facility.
The under-construction SG-III laser facility is a huge high power solid laser driver, which contains 48 beams and is
designed to deliver 180kJ energy at 3ns pulse duration. The testing ending up at September 2012 validated that the first
bundle lasers of SG-III facility had achieved all the designed requirements. And shortly later in December 2012, the first
round of running-in physics experiment provided a preliminary X-ray diagnostic result. In the testing experiment,
detailed analysis of the laser energy, the temporal characteristics, the spatial distribution and the focusing performance
was made by using the Beam Integrated Diagnostic System. The 25kJ 3ω energy produced by the first bundle lasers
created the new domestic record in China. These great progresses in the laser performance and the physics experiment
have already demonstrated that the facility is in excellent accordance with the designs, which establish a solid foundation
for completing all the construction goals.