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.
A high power, high-repetition picosecond amplifier with an all-fiber picoseconds seed source, Nd:YVO<sub>4</sub> and Nd:YAG gain medium was designed and experimentally studied. For a injected seeder laser with a repetition rate of 1 MHz and an average power of 2.34 W, a 55 W laser power output was obtained by the two-stage solid-state amplification, and the measured pulse width was 9.2 ps, and the laser wavelength was 1064.5 nm. The laser output characteristics of different repetitive modes were experimentally studied, and the laser output power was 18.4 W in the (1 × 4) MHz burst mode. Since the spectrum of the fiber picosecond seed light is much larger than the gain spectrum width of the amplifying medium, the output power of the entire system does not reach the design index. Next, the fiber seed source parameters need to be optimized to achieve a larger amplification power output.
This paper shows a novel design for a true zero-order wave-plate to introduce an accurate phase retardation with a big birefringent crystal. The true zero-order wave-plates can be processed with different angles deviating from the crystal’s axis, and the thickness could be selected from millimeter to centimeter order, which increased the mechanical strength greatly. The true zero-order wave-plates were made of NH<sub>4</sub>H<sub>2</sub>PO<sub>4</sub> (ADP) crystal, including half wave-plate (HWP) and quarter wave-plate (QWP). When the cutting angle θ is 4<sup>o</sup>, the thickness d of 1064 nm TZ half wave plate (HWP) is 2.75 mm. At the room temperature (25°C), its extinction ratio as the polarization rotator reaches 1000:1 at 1064nm by using spectroscopic method. With ADP-QWP, a 18.6 ns pulse output of Q-switched Nd:YAG laser (1064nm) is successively realized. When the static energy is 160 mJ, the dynamic energy reaches 113 mJ. The above contents provide not only good references for wave-plates fabrication of other birefringent crystals, but also more potential applications in largediameter optical systems such as ultra-high power laser, high resolution inspection equipment and astronomical observation equipment with a large-diameter ADP wave-plate.
Optical poling and frequency doubling effect is one of the effective manners to induce second order nonlinearity and realize frequency doubling in glass materials. The classical model believes that an internal electric field is built in glass when it’s exposed by fundamental and frequency-doubled light at the same time, and second order nonlinearity appears as a result of the electric field and the orientation of poles. The process of frequency doubling in glass is quasi phase matched. In this letter, the physical process of poling and doubling process in optical poling and frequency doubling effect is deeply discussed in detail. The magnitude and direction of internal electric field, second order nonlinear coefficient and its components, strength and direction of frequency doubled output signal, quasi phase matched coupled wave equations are given in analytic expression. Model of optical poling and frequency doubling effect which can be quantitatively analyzed are constructed in theory, which set a foundation for intensive study of optical poling and frequency doubling effect.
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.
This paper first studies the structure effect law in order to design a reasonable option in theory for the Final Optics Assembly(FOA)’ harmonic converter module, involved in the design of the fluid theory, including the basic equations of fluid motion, the form of fluid motion and fluid movement in the small hole. Optimizing the structure need to be applied to the simulation software, which requires the Fluent simulation principle. Then, combined with theoretical knowledge to design the overall structure of the multiplier module, It will apply the simulation software to optimize structural parameters of the board and use control system to realize it for verifying the law obtained by simulation under various conditions whether consistent with the law in actual work of the sweeping system.
Experimental research on non-critical phase-matching fourth harmonic generation with ADP and DKDP crystals are reported. The characteristics of 2ω-to-4ω efficiency as function of incident angle, crystal temperature and input 2ω intensity have been investigated in detail, and the 2ω-to-4ω conversion efficiency has been demonstrated up to 84.1% with ADP crystal and 85.1% with DKDP crystal, respectively. Nevertheless, the spatial non-uniformity of rapid grown DKDP crystal has to be improved while the temperature control uniformity should be upgraded for ADP crystal to realize large aperture high efficiency fourth harmonic generation.
Multi-FM SSD and CPP was experimentally studied in high fluence and will be equipped on all the beams of SG-III laser facility. The output spectrum of the cascade phase modulators are stable and the residual amplitude modulation is small. FM-to-AM effect caused by free-space propagation after using smoothing by spectral dispersion is theoretically analyzed. Results indicate inserting a dispersion grating in places with larger beam aperture could alleviate the FM-to- AM effect, suggesting minimizing free-space propagation and adopting image relay. Experiments taken on SG-III laser facility indicate when the number of color cycles (Nc) adopts 1, imposing of SSD with 3.3 times diffraction limit (TDL) did not lead to pinhole closure in the spatial filters of the preamplifier and main amplifier with 30-TDL pinhole size. The nonuniformity of the focal spot using Multi-FM SSD and CPP drops to 0.26, comparing to 0.84 only using CPP. The experiments solve some key technical problems using SSD and CPP on SG-III laser facility, and provide a flexible platform for laser-plasma interaction experiments. Combined beam smoothing and polarization smoothing are also analyzed. Simulation results indicate through adjusting dispersion directions of one-dimensional SSD beams in a quad, two-dimensional SSD could be obtained. The near field and far field properties of beams using polarization smoothing were also studied, including birefringent wedge and polarization control plate (PCP). By using PCP, cylindrical vector beams could be obtained. New solutions will be provided to solve the LPI problem encountered in indirect drive laser fusion.
The influence of laser beam size on laser-induced damage performance, especially damage probability
and laser-induced damage threshold (LIDT) is investigated. It is found that damage probability is beam
size dependent when various damage precursors with different potential behaviors are involved. This
causes damage probability and LIDT are different between tested under large-aperture beam and under
small-aperture beam. Moreover, fluence fluctuations of large-aperture laser beam bring about hot spots
moving randomly across the beam from shot to shot. Thus it leads to the most probable maximum
fluence after many shots at any location across components is several times the average beam fluence.
These two effects result in difference of damage performance of components in large-aperture lasers
and in small-aperture lasers.
We report a novel frequency tripler for efficient conversion of broadband high power laser pulses at 1 μ;m. The tripler is
composed of several segmented partially deuterated KDP with discrete values of deuteration. Deuteration level can be
used as a degree of freedom to alter the phase-matching wavelength of a partially deuterated KDP crystal. The
segmented partially deuterated KDP crystal is made by thermal bonding method. It has been shown that this new tripler
is capable of enhancing the acceptance bandwidth of frequency tripling. A two-segment design is presented, which is
applicable to the efficient frequency tripling of chirped pulses with a bandwidth of ~1.2-nm.
The fiber phase shifting point-diffraction interferometer (FPS/PDI) has recently been designed to measure spherical surface with high precision. The wavefront shape emerging from the fiber, which acts as the referenced wave in FPS/PDI, must be controlled precisely in design.
The rigorous theory model of fiber point diffraction is studied for instrument realization. To execute such high accurate (10<sup>-4</sup>λ) simulation, vector diffraction method must be adopted because conventional scalar diffraction theory is unsuitable when the fiber core size is comparable to wavelength. Based on the model, the influence of fiber core diameter, end-face figure and so on is studied. Some important conclusions are inferred. Firstly, the residual aberration is reduced with decreasing of fiber core size, so that the available numerical aperture decreases. Secondly, when the end face of the optical fiber is ellipse, the effect of the ellipticity should be considered. Thirdly, the oblique fiber, like ordinary fibers cut with zero face angle, generates a high quality spherical wave, but the propagation direction changes with the oblique angle. Finally, the residual aberration of diffraction wavefront becomes larger when the surface error of the end-face figure increases. The result shows that the single mode fiber used in experiment is available for instrument design and its influence over systematic error is negligible within certain numerical aperture.
In the measurement of the infrared imager, noise is the primary parameter in evaluating the quality of the infrared
imager. In the engineering application of the infrared imager,
three-dimensional noise pattern is not applied widely in the
hard technology of the infrared imager due to its pattern is complex, physical significance is not definite and visualized.
Noise parameters include the temporal noise and the spatial noise. The temporal noise can be divided into high frequency
temporal noise and low frequency temporal noise (namely 1/f noise), and the spatial noise can be divided into high
frequency spatial noise (namely fixed pattern noise, FPN) and low frequency spatial noise (un-uniform noise). The strict
definition about high frequency temporal noise and low frequency temporal noise is given in this paper. The algorithm
and measuring methods for low frequency temporal noise equivalent temperature difference are proposed. The
algorithms and measuring methods of high frequency noise equivalent temperature difference are given, ignoring low
frequency temporal noise in short-time during measuring high frequency noise equivalent temperature difference or not.
Moreover, the uncertainty of measurement results for high frequency temporal noise equivalent temperature difference is
analyzed in the paper.
The correct monitoring of thin-film thickness is one of the main problems during the course of optical thin-film
component manufacture, in recent years, the method which is spectrum intensity measurement of thin-film component
for controlling thin-film thickness has been one of the most effective methods. When this method is used Chow
spectrum intensity is real-time, correctly measured is critical. Compared with the conventional method which is
mechanical scanning by stepper motor driving the grating of monochromator and receiving by photoelectrical multiplier
tube, in structure, the author combines the grating spectrometer with the linear CCD, which makes the problem of
spectrum intensity real-time measurement better solved, the result is satisfied. In this paper, the structure of system
affecting the spectrum intensity measurement accuracy is analyzed, By experiment, the relative parameters are
determined, the spectrum wavelength is calibrated, root-mean-square error is 0.234nm, which is up to the requirement of
monitoring wavelength resolution in the course of thin-film deposition; The algorithm is used for the real-time
compensation of spectrum intensity measurement data, which make the effect of CCD photoelectrical response
non-uniformity and nonlinear less; By changing the integral time magnitude, the rate of signal to noise of the spectrum
signal is improved, it satisfies the requirement of real-time thin film thickness control.
Digital holography technology, which adopt CCD digital camera to record holograph, can get amplitude and phase
information of the sample tested respectively through processing the image. Re-focus of the sample image can be
realized by calculating complex amplitude information obtained. However, digital holograph reproduction system can't
offer any criterion which determine whether reproduction image achieve fixed-focus state when reproduction image
stands in the optimum position. Digital holography reproduction process need add an exterior criterion function, which
implement automatic focus as normal imaging system. Aimed to digital imaging automatic focusing problem of off-axis
Fresnel holography, image gradient energy method, image Laplace energy method, image shade of gray variance method
are compared from two points of theory and practice view, and present the advanced measurement method based on
spectrum band-stop filter. Experiment shows that the algorithm has some adaptability, especially image Laplace energy
method based on spectrum band-stop filter has non-skewness, monotonicity, unimodality, kurtosis and robust.
To characterize the spherical surface of extreme ultraviolet (EUV), the fiber phase shifting point-diffraction
interferometer (FPS/PDI) has recently been designed and implemented. The diffraction wavefront from an optical fiber
acts as the perfect referenced spherical wave and new-style interferometer configuration is used. The laboratory
apparatus has been put up to measure spherical surface in experiment. The main content of this paper is the key
technique of FPS/PDI about the method of interference image processing and the precision analysis for the
In experiment apparatus, a concave spherical surface is measured and a piezoelectric ceramics (PZT) is used for phase
shifting. The wrap phase distribution is got by five-step phase shifting method, and then the unweighted least-squares
phase unwrapping algorithm is optimized and used to obtain the unwrapped phase distribution. The error of spherical
figure is derived from the fitting method of Zernike polynomials. The data processing result is analyzed in comparison
with the measurement result of ZYGO interferometer. The repeat precision of the FPS/PDI is evaluated by multimeasurement.
Finally, the major error sources are discussed and some optimized methods for the system are
proposed.The results show that the interferometer has achieved worthy measurement precision and has great
The technical integration line (TIL), which is the full scale prototype for Shengguang-III laser facility (SG-III), now under construction at CAEP, will contain a neodymium glass laser system with more than 70 large (40-100 cm) optical components. Reflections from these surfaces (so-called ghost reflections) are numerous and extensive computation has been required to track them in the TIL optical system. The tremendous number of ghost paths requires a visualization method that allows overlapping ghosts on optics, and then sums them up to illustrate its potential damage on critical surfaces. Therefore, how to make an effective identification and visualization of multi-order "ghost" has been a major part of the optical design effort. This paper addresses the following aspects of TIL ghost analysis: 1, comparison of several methods for ghost energy simulation. 2, some techniques for visualization of complex optical systems in 3D space including mirrors and pinholes. 3, attempts at visualizing “ghost energy” distribution near some critical surfaces so as to provide detailed references for mitigation of ghost caused damage.
Diffraction components are applied in high power laser systems for beam shaping and harmonic separation. Because of the multi-order diffraction and multi-reflection to high power laser, the distributions of stray light energy and ghosts are much more completed in the systems than in conventional optical systems. In this paper a data structure of tree is presented for describing the stray light caused by multi-order diffraction and multi-reflection. All the nodes of the tree can be dynamically saved and be deleted, and the intermediate results those are useful for the next calculation step can be reserved in RAM. Using this method the multiple repeated calculations in conventional stray light analysis methods such as Monte Carlo technique are avoided and the analysis time is reduced. According to the paraxial tracing, the software which can be used for analyzing the stray light caused by multi-order diffraction and multi-reflection in high power laser systems is developed and the stray light tree of a laser system based on paraxial tracing is built. As shown by the example that this algorithm is available for quickly analyzing stray light in the systems including diffraction components, and the ghost positions with energy descriptions can be given by the software. The ghosts those are harmful to the important components will be picked.