Under-sampling Fourier Transform Spectroscopy Measurement Of Broad-spectrum Laser Spot Profile

The rapid development of ultrafast laser technology provides unprecedented extreme physical conditions and new experimental methods.With its ultra-short time characteristics and ultra-high peak power,wide-spectrum lasers are widely used in various fields such as physics,chemistry,and biology.Precise measurement of broad-spectrum laser spectra and spot patterns,especially frequency-resolved laser spot patterns,is of great significance to the study of ultra-fast processes in atomic and molecular science,in-depth understanding of the mechanism of laser material interaction,and optimization of laser precision machining processes.Due to the large frequency domain bandwidth of ultrafast lasers,general measurement techniques are based on the algebraic superposition of the light intensity distributions of different frequency components,and cannot distinguish the differences between laser spot patterns of different frequency components.If the existing spectrometer is used to measure the laser spectrum,due to the incident slit selection effect of the imaging spectrometer,the information on the lateral distribution of the laser spot in the vertical slit direction is missing,and a complete two-dimensional laser spot spatial distribution cannot be obtained.For a two-dimensional laser spot,measuring its hyperspectral image based on Fourier transform interferometry is an important method,but the mature application of Fourier transform imaging technology is more in the infrared region,and the research in the visible and ultraviolet bands is not many.This is because the requirements for sampling points in Fourier transform interferometry should meet the sampling theorem,and the stability and accuracy of the moving device are extremely high when measuring short-wavelength laser spots.This paper proposes a wide-spectrum laser spot profile hyperspectral measurement technology based on Fourier transform spectroscopy,which can measure the two-dimensional spatial distribution information of the light intensity of different frequency components of broadband ultrafast lasers under the condition of under-sampling.The theory deduces the feasibility of the scheme,and the simulation simulates the high spectral resolution of laser pulse spots in the visible light band of 760 nm to 820 nm and the extreme ultraviolet band of15 nm to 60 nm.The former was simulated in over-sampling and under-sampling cases,and the hyperspectral resolution results of the laser spot profile in the two cases were compared,which proved the feasibility of the scheme under under-sampling;The latter was simulated under under-sampling and compared with the preset pulse and the simulation results,which proved the feasibility of the scheme in the extreme ultraviolet band.Afterwards,a high-spectral resolution experiment was carried out on the 37 fs laser pulse spot of 770 nm to 810 nm.