Study And Implementation Of A New Type Of All-Optical Ultrafast Imaging System

Currently, the most widely applied ultrafast diagnosis technology is streak camera, framing camera and pump-probe method. But these methods are weak in some aspects. For example, the streak camera can only provide one-dimensional images; the temporal resolution of framing camera is low relativity; the pump-probe method can provide a multidimensional motion picture of the ultrafast process, and the temporal resolution of pump-probe method is much better than any conventional camera. But it requires the event under observation to be relatively simple and easily reproducible, rendering the method is weak in studying difficult-to-reproduce or non-repetitive events such as explosions, Brownian motion and chemical reaction.In this letter, we study and design an all-new ultrafast imaging system which is based on all-optical technology--All-Optical Ultrafast Sequentially Timed Imaging System by Femtosecond Laser. We verify the scheme of design in our lab. This system can shoot the ultrafast process directly which cannot be detected by conventional method and help us to get the high pixel resolution motion pictures without the need for repetitive measurements to construct a motion-pictures. This all-new system is a powerful tool for studying fast dynamics in photochemistry, spintronics and plasma physics.In this letter, we analyze and compute the pulse stretching unit, pulse shaping unit, spectrum mapping unit, imaging optical path and optical path of delay in theory. We verify ultrafast imaging system in experiment and make use of this system to acquire data of ultrafast process.The main work in this paper includes some aspects as follows.(1) We set up the pulse stretcher, compare and analyze the different pulse stretchers with each other. By using the 750 mm high dispersion glass as the medium of pulse stretching, we eventually make the input pulse(25fs) be stretched to 26 ps by experiment.(2) Based on the analysis of ultra-short laser pulse shaping, we use the phase only spatial light modulator as the MASK to build up the laser pulse shaping optical 4f system and shape the input laser pulse(25fs), thus we achieve the train of discrete daughter pulses with equal intensity.(3) We design a custom optical element which is named “periscope array” and cylindrical mirror by Solidworks and ZEMAX and build up the spectrum mapping optical 4f system to achieve discrete daughter pulse in space.(4) We set up the delay line and imaging optical path and use them to research the observation example in detail. Finally we get the motion pictures of air ionizing excited by femtosecond laser(25fs). The exposure time of single picture is 912 fs, frame interval is 6.39 ps and pixel resolution is 200×200 pixels.