多FROG构型下非方形迹的超短脉冲重建  

Ultrashort Pulse Reconstruction from Non-Square FROG Traces in Different Geometric Schemes

作　　者：毛安君 刘呈普[1] Mao Anjun;Liu Chengpu(State Key Laboratory of High Field Laser Physics,Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences,Shanghai 201800,China;University of Chinese Academy of Sciences,Beijing 100049,China;Faculty of Mathematics and Physics,Huaiyin Institute of Technology,Huaian,Jiangsu 223001,China)

机构地区：[1]中国科学院上海光学精密机械研究所强场激光物理国家重点实验室,上海201800 [2]中国科学院大学,北京100049 [3]淮阴工学院数理学院,江苏淮安223001

出　　处：《中国激光》2021年第7期101-109,共9页Chinese Journal of Lasers

基　　金：国家自然科学基金(11674342)。

摘　　要：在充分考虑测量仪器特点的基础上设计非方形迹图,具体对原方形迹图进行如下三种操作:频率轴的低通滤波,降低非线性过程中相位匹配带宽的要求;频率轴的上采样,充分利用光谱仪的高分辨率;延时轴的下采样,明显减少测量耗时并提高精度。由此基于层叠成像算法对二次谐波、偏振门和交叉相位调制三种构型的频率分辨光学开关(FROG)使用非方形迹图进行脉冲重建并对重建能力进行比较,发现在频率轴“1/3×”低通滤波和“4×”上采样的情况下,交叉相位调制构型能够在仅使用8个延时(原方形迹图需128个)的情况下成功实现脉冲的重建。因延时操作为FROG技术中最耗时的环节之一,减少其次数可有效促进FROG用于超短激光脉冲的实时测量。Objective The research on the electric field of ultrashort laser pulse has a wide application prospect.The ultrashort femtosecond laser pulse is used in many scientific and engineering domains,such as ultrashort spectroscopy,quantum coherent modulation,and ultra-intense laser physics.A typical method of measuring ultrashort laser pulse is the frequency-resolved optical gating(FROG).Using FROG,we first split the pulse into two replicas and then apply a time-delay to one of them.Next,we allow them to interact in a nonlinear process to generate a signal,in which we use spectroscopy to measure the spectral intensity.Finally,we tune the time delays to obtain the spectral intensities of a set of nonlinear signals,which constitute a spectrogram named FROG trace.A phase retrieval algorithm is always required to reconstruct the original laser pulse because only the intensities are recorded in FROG trace.As an efficient phase retrieval algorithm,the prominent component general projecting algorithm(PCGPA)is widely used for ultrashort pulse measurement.However,PCGA brings several practical problems for the FROG measuring process because PCGPA requires that the trace be a square one and that its frequency axis and delay axis coordinates are coupled by fast Fourier transform.According to the different applications of the nonlinear process,FROG can also be realized in different geometrical schemes,for example,second harmonic generation(SHG),polarization gate(PG),and cross-phase modulation(XPM).In this study,we aim to(i)build a non-square FROG trace by taking the features of the measuring devices into fully account to realize successful pulse reconstruction and avoid the drawbacks accompanied by PCGPA and(ii)compare the retrieving results in different geometries to select a more efficient and practical one.Methods First,we build the non-square trace by applying the following three transformations on the 256×256 square FROG trace(Fig.1):(i)low-pass filtering in the frequency axis(F_LPF),(ii)up-sampling in the frequency axis(F_US

关 键 词：测量 超短脉冲表征 频率分辨光学开关 光束构型 非方形迹图 

分 类 号：O439[机械工程—光学工程]