研究目的
To investigate the variation of optical properties of K9 glass before and after laser induced damage in the terahertz band.
研究成果
The study demonstrated that THz time-domain spectroscopy technology is effective for analyzing the optical properties of K9 glass before and after laser-induced damage. The optical parameters extracted can be used to analyze the effect of laser-induced damage on the optical property and microstructure of K9 glass, providing a technical basis for studying the mechanism of laser-induced damage of optical elements.
研究不足
The terahertz spot diameter is about 2 mm, and the energy is at micro watt level, limiting the measurement to damage points with diameter larger than 0.6 mm. Smaller damage points require smaller test beam and higher power.
1：Experimental Design and Method Selection:
The transmission terahertz time-domain spectroscopy system was used to test the undamaged and laser-damaged K9 glasses. The system includes a femtosecond laser, terahertz generation device, terahertz detection device, delay device, and sample stage.
2：Sample Selection and Data Sources:
K9 glass samples of f30×2 mm were selected. Laser-induced damage was performed using Nd:YAG solid-state laser with different energy densities.
3：List of Experimental Equipment and Materials:
MaiTai laser with center wavelength of 800 nm, pulse width of 60 fs, repetition frequency of 80 MHz, and output power of 950 mW; GaAs photoconductive antenna for terahertz wave generation; ZnTe electro-optic crystal for detection.
4：Experimental Procedures and Operational Workflow:
The femtosecond laser pulse was divided into pump light and detection light. The pump light focused on GaAs photoconductive antenna to generate terahertz wave, which was then collimated and focused on the sample. The detection light and terahertz pulse passed through ZnTe crystal, and the voltage output by the balance detector reflected the electric field intensity of terahertz wave.
5：Data Analysis Methods:
The optical parameters were calculated based on the physical model proposed by Dorney and Duvillaret, using Fourier transformation to obtain frequency domain signals and then calculating refractive index and absorption coefficient.
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