Study On The Measurement Of UV Femtosecond Laser Pulse Duration

Ultrashort laser pulse technology was powerful tools for the study of ultrafast phenomena. Nevertheless the measurement of pulse duration which is important to the development and the application of laser technology is a challenging problem.the development of ultrashort UV laser technology profits from the progress of laser technology itself, as well as the advance of the measurement methods for the uv pulse duration. So far, the autocorrelation, frequency-resolved optical gating (FROG) and spectral phase interferometry for direct electric-field reconstruction (SPIDER) are the general methods for the measurement of optical pulse duration. In the autocorrelation method, pulse was split into two beams, and intersected non-collinearly in the nonlinear super-sensitive crystal. pulse duration can be estimated from the relevant signal. The autocorrelation method is simple, however, it is inapplicable to the UV region due to the phase mismatching. In addition, nonlinear crystal phase matching bandwidth is limited and can not have the same conversion efficiency for all the frequency components, resulting in the distortion spectrum. Thus, although the autocorrelation method is very simple and easy to understand, it can not be directly applied to ultraviolet pulse measurement. FROG is a derivative of autocorrelation, it is a completely background-free auto-correlator, which can measure accurately the UV pulse duration, spectral Bandwidth and phase in theory. but it involves complex measurement procedures and calculation procedures, cumbersome technical operations, and the pulse is also given only approximate information. Therefore, FROG is not conducive to measure in real-time. SPIDER is a self-reference type of spectral interference technique, it's advantage is that the reconstruction algorithm is convenient, the accuracy of spectral reconstruction which is not sensitive to the nonlinear crystal phase-matching bandwidth and spectral response of the detector depends only on the interval of spectral interference fringes. However, it can not be given pulse duration. In short, there is no simple and fast method for the measurement of extreme ultraviolet ultrashort laser pulse duration.In this paper, the measurement of UV ultrashort pulse based on the two-photon ionization and cross-correlation in air is demonstrated. It is shown that our experiments can obtain data reliably in real-time. The intensity of signal is threefold higher than that of the background. The resolution of 8.3fs is demonstrated. The relatively good results are also acquired with the cross-correlation measurement system. But the accidental errors in calibration cannot be able to avoid due to the deviation between two pulses, which caused the instability of the experimental results. The measurement of UV pulses duration only based on the cross-correlation is not reliable. However, we analyzed the signal peak position versus the delay between probe pulses and pumps, as well as the dependences of signal peak position on the intersection angle between the two light beams. The experimental results show that the appropriate intersection angle and crystals are necessary for the accuracy of data. In addition, we can measure and control the precision delay of femtosecond magnitude by this system, and achieve light to light conversion in delay measurements of two beams light.