Research On Image Threshold Laser Film Damage Threshold Testing System

As an important part of the laser and optical system,the optical dielectric film severely restricts the development of lasers and other optical devices due to its resistance to damage.In order to realize the development of the optical equipment system toward high energy,high stability,and long standby,it is necessary to accurately determine the damage threshold of the film.Therefore,it is of great significance to develop an intelligent,on-line film damage threshold test system.The study of the damage mechanism of the thin film shows that the intrinsic absorption of the thin film,the avalanche ionization,the multiphoton ionization,and the impurity defect^[5]all affect the testing of the film damage threshold.In order to ensure that the damage threshold of the optical media film is reasonable,applicable,and universal,the system adopts the 1-on-1 film damage test method specified in ISO11254.Aiming at the shortcomings of traditional optical media film damage judgments that are subject to subjective factors,complex decision process,high environmental requirements,and inability to determine on-line,a high-sensitivity,high-reliability,simple-to-use image measurement method is proposed.Non-contact film damage determination.For the existing film damage test system,Gaussian beam is often used as the optical medium film irradiation source,and there is a problem of uneven energy distribution.In this paper,the flat top beam obtained by beam shaping a Gaussian beam using aspherical lens group is used as a test light source.Effectively reduce the test error caused by the uneven beam.The design of the optical splitter unit and the attenuator unit is described in detail in order to meet the light source requirements of the sample test,and the energy of the light beam reaching the image sensor will not appear unresponsive or oversaturated within the effective measurement range.The system uses the embedded processor STM32 to complete the automatic positioning of the sample test unit,the laser diode pulse light source energy adjustment,the laser power source external trigger control light emission,the CCD camera synchronously triggers the acquisition laser spot image,etc.;using field programmable gate array FPGA to drive the OV5640 camera Acquisition of film damage images,parallel implementation of Sobel edge detection algorithm and corrosion expansion filter algorithm;In order to ensure that the test system pixel processing clock and pixel output clock match to ensure the pixel output and VGA display synchronization,FPGA is also used to design the asynchronous FIFO and SDRAM external memory The binarized film damage image is stored in ping-pong.The simulation timing of each part is given in this paper.Finally,using a designed test system,a high-reflection film?HfO₂ andSiO₂?with a film material and a Nd:YAG solid-state laser with a wavelength of 1064 nm and a pulse width of10 ns was tested.By applying multiple sets of laser energy to the film,at least 100 test point information obtained is uploaded to the PC.After the PC solves,the damage probability data and the film damage threshold of each group under different laser energy are determined.Multiplicative linear fitting gave a zero probability damage threshold of12.25J/cm²for the high-reflection film?HfO₂ andSiO₂?.The final test results show that the system can achieve high-precision,fast on-line testing of highly reflective optical media films.