This work proposed a temporal phase-shift digital shearography system for simultaneous measurement of first-order displacement derivative in orthogonal shear directions. Dual lasers with wavelengths of 532 and 637 nm, three splitter prism structure, two dichroic mirrors with different response wavelengths, and the color complementary metal-oxide-semiconductor are used in the system. Two dichroic mirrors can be used as shear mirrors to realize shearing in orthogonal directions at the same time. The system realizes the measurement of the first-order displacement derivative information in the orthogonal direction of the round metal aluminum plate of diameter 250 mm. The experimental results show that the overall displacement integral peak to valley error in the x and y directions is 2.7% to 14.8%, which verified the reliability of the system.
Laser-induced damage threshold is an important parameter to evaluate the performance of the optical components in high power laser systems. An automated test system is presented to measure multiwavelength laser-induced damage threshold. The presented system can be able to operate the 1-on-1 and R-on-1 methodologies at 1064nm, 532nm, and 355nm. Some solutions are presented to improve the measurement efficiency and the reliability. Experimental results are also provided to confirm the capabilities of the proposed test system.
The damage morphology information is crucially important for optical components to analysis laser-induced damage resistance. Because of complex configurations, some high-precision and high-resolution techniques have limitations to detect in-line damage sites. Thus, a modified lateral shearing interferometer is proposed to obtain three- dimensional damage morphology information. In the presented method, the original beam passing through damage sites is magnified by a microscope system, and separated by a parallel plate into two sub-beams. In the overlap region of the sub-beams, the interference pattern can be used to extract the damage morphology information. Systematic errors are also eliminated from obtained interferograms before and after pulse laser irradiation, respectively. Experimental results are presented to confirm the feasibility of the proposed lateral shearing interferometer for in-line damage morphology measurement.
This work presents the influence of polarization orientation on bulk damage performance of type I doubler KDP crystals under different wavelengths pulses exposure. Pinpoints densities (PPD) and the size distribution of pinpoints are extracted through light scattering pictures. The obtained results strongly indicate that the measured PPD as a function of the fluence are both wavelength and polarization orientation related, while neither fluence nor polarization orientation affect the size distribution of pinpoints. We also find that the bulk damage characteristics can divide into three sorts with respect to the wavelength, suggesting the existence of different species of precursors and different mechanisms responsible for bulk damage initiation in SHG KDP crystals.
A systematic error calibration method is presented to improve the measurement accuracy of lateral shearing interferometry (LSI). This method is used to remove the most significant errors: geometric optical path difference (OPD) and detector tilt error. Difference fronts in the 0° and 90° directions are used to reconstruct wavefront using difference Zernike polynomial fitting. And difference fronts in the 45° and 135° directions are also used to reconstruct wavefront. The coefficient differences between the reconstructed wavefront are generated from geometric OPD and detector tilt error. The relationship between Zernike coefficient differences and systematic parameters are presented based on shear matrix. Thus, the distance of diffracted light converging point (d) and detector tilt angle can be calculated from the coefficient difference. Based on the calculated d and detector tilt angle, the geometric OPD and detector-tilt induced systematic errors are removed and the measurement accuracy of LSI is improved.
The investigation of the influence polarization orientation on damage performance of type I doubler KDP crystals grown by the conventional growth method under under 532nm pulse exposure is carried out in this work. The obtained results point out the pinpoint density (ppd) of polarization parallels the extraordinary axis is around 1.5× less than that of polarization parallels the ordinary axis under the same fluence, although polarization has no influence on size distribution of pinpoints. Meanwhile, crystal inhomogeneity is observed during experiment.
A multipurpose laser damage test facility delivering pulses from 1ns to 20ns and designed to output energy 40 Joule at 351nm is presented. The laser induced damage threshold (LIDT) measurement and test procedure are performed. The original system consist of the online detection system based on the microscopy and an energy detection device based on the scientific grade Charge Coupled Device (CCD) which provides the method to measure the LIDT with high accuracy. This method is an efficient way that allows measuring a small area fluence which the defect exposed. After complete test procedure and data treatment the damage position of the defect has been found. Then we can obtain the local fluence of small area when the damage occurred. This procedure provides a straightforward means of laser-damage threshold obtained from the test method. Damage correlation of measures is discussed in connection with present theoretical understanding of laser damage phenomenon. The damage process in transparent dielectric materials being the results of complex processes involving multi-photon ionization, avalanche ionization, electron-phonon coupling, and thermal effects. Those complex processes lead to the damage on the optical surface. We performed a method to measure the local fluence which defects irradiated with high accurate.
In this paper, we investigated the effects of laser pulse width on laser-induced damage. We measured the damage threshold of K9 glass
and UBK7 glass optical components at different pulse width, then analysis pulse-width dependence of damage threshold. It is shown
that damage threshold at different pulse width conforms to thermal restriction mechanism, Because of cm size laser beam, defect on
the optical component surface leads to laser-induced threshold decreased.
For researching the influence factors of the damage threshold test results, the 1 on 1 test program and data processing on fused SiO2 optical elements was numerically simulated with Monte Carlo method. The influence of the surface defect density and the target test spots area for the test results of damage threshold was studied. The numerical simulation results indicate that the damage threshold of optical elements can't be accurately evaluated with 1 on 1 test program if the surface defects have the characteristics of both low density and low damage threshold. The zero-probability damage threshold isn't equal to the minimum energy density when the laser induced damage of optical element appears. This work is helpful for understanding the 1 on 1 test result and has important reference value in the actual damage threshold test of optical elements using 1 on 1 test method.
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