基于波长分幅和参量放大的超快多幅实时成像技术的研究

Developing imaging technology with extreme-high photographic frequency is very significant for some scientific studies in extreme short time scale, and has been proved to be an indispensable tool to promote the developments of frontier scientific investigation, national defense, spaceflight and so on. This project aims at developing an imaging technology with extreme-high photographic frequency, extreme-high time resolution and muti-frames to record the ultrafast non-repeatable processes. A collinear pulse train with different wavelength is generated by using chirped pulse shaping technology, for the imaging sampling of the event at different moments with fs resolution. For the first time, the sampling pulses are separated spatially without astigmatism by using some grating pairs, and finally image onto their own CCD devices. The time resolution of this method is independent of the response time of the CCDs, and the signal recording time of the medium can be far longer than the temporal resolution of the image, which reduces the sensitivity requirements of the CCDs. Chirped pulse amplification technology is first introduced to improve the intensity of the imaging information and the recorded signal-to-noise ratio, and also reduce the image distortion in the ultrashort laser pulse amplification process. For the first time, new digital processing technology is developed to recover the lost information by pump non-uniform and phase mismatching in OPA. As a result, our work will present 4-frame images of a ultrafast event with photograph frequency more than 100Gfps, time resolution as high as 100fs and space bandwidth product as high as 30000.

发展超快实时成像技术对于研究极短时间尺度下的科学问题具有极其重要的意义，并推动前沿科学研究、国防以及航天等方面的发展。本项目旨在发展一种对非重复超快过程具有极高摄影频率、极高时间分辨率的多幅成像技术。首次利用啁啾脉冲整形技术，获得不同波长、空间共线传播的超短脉冲序列，对事件不同时刻进行飞秒分辨成像取样。首次利用色散效应将取样脉冲在空间上分离并成像在各自面阵CCD 上。该方法的时间分辨率与CCD 的响应时间无关，降低了超快成像对CCD 灵敏度的要求。首次引入啁啾脉冲参量放大技术提高超快成像的强度和记录信噪比，同时降低图像信息在放大过程中的畸变。利用计算技术恢复参量放大过程中丢失的图像信息，以提高像的空间分辨率。研究结果预期对某一超快时间事件实现约100fs时间分辨率、大于100Gfps 摄影频率以及高空间分辨率（空间-带宽积约30000）的4幅极高速成像。

发展超快实时成像技术对于研究极短时间尺度下的科学问题具有极其重要的意义，并推动前沿科学研究、国防以及航天等方面的发展。本项目旨在发展一种对非重复超快过程具有极高摄影频率、极高时间分辨率的多幅成像技术。首次利用啁啾光照明、超短脉冲取样的级联非共线光参量放大设计，对事件不同时刻进行飞秒分辨成像取样，获得时序多幅闲频光成像。提出新型II类相位匹配非共线设计，消除闲频光拖尾现象，既能大大提高闲频光图像质量，又有利于各级超快闲频光图像的自然空间分离。提出了非共线角度非临界相位匹配光参量放大技术，能够有效提高光参量放大成像的信息量和空间均匀性。我们的单次超快多幅超快成像系统相关指标已经全部达到原有研究目标的要求，实测指标为：时间分辨率100fs，摄影频率10^12fps，空间带宽积73000，画幅数4幅。该技术对于揭示诸如激光等离子体的形成和演化、激光尾波场加速相对论性电子束、超快化学/医学分子动力学过程等不可重复过程的机理有重要的意义。