Measurement of the low damage threshold defects in a large aperture fused silica glass is of great significance. Currently, the popular characterization method for detecting the low damage threshold defects is via measuring the optical absorption of a fused silica glass using the surface thermal lensing technology. However the detecting area of a single shot in this method is too small, typically around 10×10 microns, so if a large aperture fused silica glass in the size of 400×400 mm is to be measured, it would take approximate 100000 hours to complete the measurement, which is obviously not acceptable. Here, we report a fast measurement technique for obtaining the low damage threshold defects in a large aperture fused silica glass according to its fingerprint spectrum, for the fused silica optical glass in the size of 400×400 mm, measurement of the low damage threshold defects in the whole surface in several hours is achievable.
The measurement of the spectral diffraction efficiencies of a diffraction grating is essential for improving the manufacturing technique and for assessing the grating’s function in practical applications. The drawback of the currently popular measurement technique is its slow speed due to the hundreds of repetitions of two kinds of time-consuming mechanical movements during the measuring process. This limitation greatly restricts the usage of this technique in dynamic measurement. We present here a motionless and fast measurement technique for obtaining the spectral diffraction efficiencies of a plane grating, effectively eliminating the aforementioned two kinds of mechanical movement. We estimate that the spectral measurement can be achieved on a millisecond timescale. Our motionless and fast measuring technique will find broad applications in dynamic measurement environments and mass industrial testing.
In order to study the scaling laws of optical components, we set up a model based on the heat conduction theory and thermodynamic theory. Then the similarity theory was used to the model analyzation. Finally, we demonstrate three conclusions which are related to the practical engineering application. The first one is that thermal damage behaviors of different scale optical components are similar when the linear power density of irradiated laser are the same. In other words, we should use the linear power density to represent the resistance of damage tolerance for optical components The second one is the judgement standard of scram time. We find the scram time of large-aperture system is certain times as much as the scram time of small-aperture system. The third one is about how to design the scaled experiment can we make two different scale laser systems obey the similar thermal damage behaviors. This study is of great help for the damage prevention of the optical components.
The thermal stress damage of optical elements always restrict the development of high power laser system. We studied the thermal damage mechanism of the optical elements with contaminants induced by high power continuous wave (CW) lasers. An experiment was carried out by a self-build optical element testing platform and a model based on the temperature field theory and thermodynamic theory was set up. We recorded the thermal stress damage process based on a 10 kW/cm<sup>2</sup> level mid-infrared continuous wave laser. Then we calculated the thermal damage process of optical elements. The calculated results are in agreement with our experimental record. The results showed the success of modeling calculation in the thermal damage mechanism caused by contaminants.
In this paper, the concept of a mesoscopic method with high-speed and high-sensitivity is proposed for characterization of surface defects for large optics. The technology is a comprehensive integration of laser scattering method and highly sensitive photothermal method. The principle, experimental setup and preliminary measurement results are presented in detail in the paper. A statistical model for evaluation of mapping results of defects is also proposed to show the effectiveness of the comprehensive metrology method. The proposed method can detect non-destructively surface defects with high-speed and high-sensitivity at the mesoscopical level. It is a promising novel tool for mapping defects in meter size optics and hence it can provide clues to eliminate defects during the manufacturing processes and march toward “defect-free” optics.