Accurate temporal characterization both in intensity and phase distribution is important in the diagnosis of the petawatt (PW) class. We present a single-shot picosecond frequency-resolved optical gating (ps-FROG) setup based on an autocorrelator with ps measurement range that is spectrally resolved through a fine grating. The modified ptychographic-based algorithm with a changing update coefficient was used for the reconstruction of the pulse distribution; it can better adapt to the reconstruction of pulse with a large time–bandwidth product. We calibrated and verified the homemade ps-FROG in a 100-μJ ps laser system and used it to characterize the pulse distribution generated by the PW laser system of the Shen Guang II facility. The system shows good performance and high accuracy in reconstructing the intensity and phase distributions of a ps pulse, which provides reference for accurately adjusting the grating pair to acquire the pulse width as a preset.
In high power laser system, the wavefront quality of large optic elements in the mid-frequency region plays a critical role in the system performance and safe operation. A simple and efficient measurement method for mid-frequency wavefront error is used, which employs the extended ptychographical iterative engine algorithm and has simple structure, low environment requirement and flexible adjustable frequency ranges. This method has been successfully implemented for the wedge focused lens to achieve accurate mid-frequency measurement. Further it can be extended to a wide range of large optical components, especially for which the wavefronts are not easy to be measured using interferometers.
3ω laser damage of fused silica optics is the bottleneck of high power laser systems for ICF. Excellent beam quality plays an important role in improving the anti-damage capability of final optics system. We have developed a new optical field measurement technology based on computational optical imaging. With the high power laser prototype of SGII-UP facility, damage resistance of final optics was experimentally studied. The near filed of laser beam was measured with a high resolution to study the effects of modulation and propagation on laser damage. The near field improvement of high power laser beam are reported and the influence of near filed quality on damage performance of final optics are discussed. The development of the defect detection techniques of final optics are introduced. Finally, we present the development perspective of final optics system for ICF laser driver. At present, the damage resistance capability of final optics assembly is 6J/cm2 at normal operation, we will continue to improve the ability in the next step of work.
Stress measurement is significant to evaluate and predict optical behaviour of the birefringence components. The separation of two principal stress components is a difficult problem due to the coupling between them. A new PIE-based stress measurement method is proposed. Combining with the four-step phase-shifting measuring method, the complex amplitude transmittance functions of the sample in different phase-shifting states are reconstructed. Then the quantitative stress birefringence information are extracted respectively from the amplitude information and phase information. This method can achieve the complete stress information measurement and is especially suitable for the large-size samples.
International standard ISO 10110-7 sets a strict limit on the size and quantity for surface defects of an optical element. For high-power laser, sub-beams caused by defects with different distributions interfere with each other in the transmission process, causing beam quality complex changes. So it is necessary to make a clear limitation on relative position of defects, thereby giving the standard a more comprehensive supplement. Based on the diffraction theory, the changes of beam modulation are studied. The influence of scratch depth on the distribution of near field beam modulation is also taken into account. Results demonstrate that when two parallel scratches are on the same or different surfaces of an element, they produce more severe modulation than single scratch, and the maximum modulation can be increased to 1.5 times. Meanwhile more strict requirements for scratch depth are put forward. The results could provide reference for the determination of defects specifications for large-diameter optical elements in high-power laser systems.
This paper proposes a new method for measuring three-dimensional vibrations. By a spherical cooperative target, the
system realizes interference from a spherical wave and a plane wave. It solves the problem of complex changes in
interference fringes when two spherical waves are used to measure three-dimensional vibration. And the vibration
calculation is very simple. Meanwhile, the interferometer integrates two interference arms into a beamsplitter by coating
design and can monitor the stability of the system itself. Theoretical analysis and experiment are performed. The
experiment results indicate that the method can monitor three-dimensional vibrations accurately.
A phase retrieval algorithm which only needs to measure the intensity distribution at two positions was used
to reconstruct laser wavefront. It was further applied in high power laser. Results were obtained from the phase retrieval algorithm in the visible band, and the effects of measurement error on the phase retrieval process have been simulated. This algorithm is not sensitive to measurement error, but sensitive to the relative distribution of light intensity.
This paper presents a new method for measuring vibration based on interference from two spherical waves. By
integrating the two interference arms into a beamsplitter cube by reflective film and the probe beam being divided into
two parts, the interferometer can distinguish that the vibrations are from the monitored optical components or from laser
interferometer system itself. At the same time, because the two interference waves are spherical, it can realize monitoring
the three-dimensional vibrations. The experimental setup has advantages of being stable and reliable with an integrated
structure. Theoretical analysis and experimental demonstration are performed. The experiment results indicate that the
method can monitor three-dimensional vibration sensitively.