Direct linear measurement of ultrashort light pulses with a picosecond streak camera

The durations of ultra-short (4–7 psec) laser pulses have been directly measured with an image tube streak camera designed for time resolution in the picosecond region. The camera was calibrated with simultaneously recorded two photon fluorescence pulse profiles and it is shown that a time resolution limit of ≈1 psec should be possible with this system.     

X-ray streak camera observations of laser produced plasma corona development

Combination of pinhole imaging of laser produced plasma soft X-ray emission and X-ray streak photography allows simultaneous space and time resolved study of the axial development of the high density region of the plasma created from a plane Cu target by a 6 nsec 1.06 μ laser pulse.     

Investigation of viscosity dependent fluorescence lifetime using a synchronously operated picosecond streak camera

Exciting with picosecond pulses from a mode locked cw dye laser and using the Synchroscan continuously operating streak camera, the variation in the fluorescence lifetime with viscosity over the range 0.5 cp–250 cp of some mode locking and potential mode locking polymethine dyes of the cyanine family were investigated. The measured lifetimes were found to follow a ∼2/3 or 1/3 power dependence of the viscosity η.     

条纹相机系统在激光脉冲整形测量中的应用

针对采用脉冲堆积法进行激光脉冲整形后获取的宏脉冲,介绍了基于条纹相机观测其纵向分布的基本原理。阐述了测量系统中的硬件配置功能以及脉冲堆积原理,并描述了使用条纹相机专用软件测量激光脉冲的详细步骤和操作界面。研究了测量系统中时序控制的调试对观测脉冲堆积后的宏脉冲的影响并给出了测量结果和测量误差分析。结果表明:采用脉冲堆积法所获得的激光脉冲整形效果非常理想,整形前激光脉冲的半高全宽值约为3.82 ps,整形后约为15.3 ps,且平顶部分的脉宽为11.5 ps,上升沿和下降沿均为1.9 ps。     

X射线条纹相机阴极制备及其绝对标定

为了提升X射线条纹相机阴极性能,提出了一种X射线条纹相机阴极的制作方法,采用此方法制作的阴极衬底薄膜使用聚碳酸酯作为原材料,厚度仅为300nm,可较大程度降低对X射线的C吸收边效应,对提升阴极性能具有较大益处。利用北京同步辐射光源(BSRF)对制作的Au阴极和CsI阴极进行了绝对标定,给出了两种阴极在60~5500eV能区范围内的绝对谱响应灵敏度,标定结果表明CsI阴极在60~5500eV整个能区范围内都具有较高的谱响应灵敏度,即使在C吸收边位置谱响应灵敏度也只降低了约90%,表明阴极性能得到较大提升。     

X射线条纹相机阴极制备及其绝对标定

为了提升X射线条纹相机阴极性能,提出了一种X射线条纹相机阴极的制作方法,采用此方法制作的阴极衬底薄膜使用聚碳酸酯作为原材料,厚度仅为300 nm,可较大程度降低对X射线的C吸收边效应,对提升阴极性能具有较大益处。利用北京同步辐射光源（BSRF）对制作的Au阴极和CsI阴极进行了绝对标定,给出了两种阴极在60~5500 eV能区范围内的绝对谱响应灵敏度,标定结果表明CsI阴极在60~5500 eV整个能区范围内都具有较高的谱响应灵敏度,即使在C吸收边位置谱响应灵敏度也只降低了约90%,表明阴极性能得到较大提升。     

Time-resolved streak camera system with solid state laser and optical parametric generator in different spectroscopic applications

Apparatus to study time-evolution of emission spectra over very wide time and spectral range is described. Excitation part of the equipment consists of solid state Nd:YAG laser and optical parametric generator. The heart of the detection system consists of spectrograph and streak camera. The significance of optics and electronics built in the system for proper, fast and convenient measurements is underlined. The results of donor-acceptor energy transfer in a rigid polyvinyl alcohol matrix serve here as an example of application our equipment to study complex systems.     

利用皮秒脉冲激光驱动瞬态X射线激光

报道了利用皮秒激光驱动产生瞬态类镍银X射线激光的实验结果.采用一路脉冲宽度为数百皮秒的激光作为预脉冲，配合另一路皮秒激光作为主脉冲联合驱动平面靶，获得了一定强度的类镍银X射线激光输出，输出能量约为5—10nJ. 关键词： 瞬态X射线激光 长短脉冲联合驱动 皮秒脉冲激光     

Generation and characterization of a bright X-ray source using picosecond laser

High-resolution soft X-ray spectra of H-like and He-like ions were produced from laser irradiated silicon and aluminum targets. Plasma size was about 100 μm. X-ray spectra were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the inter combination lines of He-like ions, with the results of model calculations. Such comparison gave average values of the electron density N _e=(1?1.9)×10²¹ cm^?3 and the electron temperature T _e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. According to our estimations, more than 10¹² photons were produced within the resonance line spectral width and in the solid angle 2π steredian during the total decay period.     

Soft picosecond X-ray laser nanomodification of gold and aluminum surfaces

Experimental and theoretical investigations of aluminum (Al) and gold (Au) surface modification by soft X-ray laser pulse are presented. Well-polished samples of Al and Au are irradiated by ps-duration pulse with wavelength of 13.9 nm at the energy range of 24–72 nJ. Differences in the melting and the ablation processes for those materials are observed. It is shown that at low laser pulse energy, the nanoscale ripples on the surface may be induced by melting without following ablation. In that case, the nanoscale changes in the surface are caused by splash of molten metal under gradient of fluence. At higher laser pulse energy, the ablation process occurs and craters are formed on the surface. However, the melting determines the size of the modified surface at all ranges of the laser energies. For interpretation of experimental results, the atomistic simulations of melting and ablation processes in Al and Au are provided. The calculated threshold fluencies for melting and ablation are well consistent with measured ones.     

Plasma satellites of X-ray lines of ions in a picosecond laser plasma

We present the results of our measurements of the spectra for multicharged ions in a plasma produced by moderately intense (about 10¹⁷Wcm^?2) picosecond laser pulses. They suggest the existence of intense plasma oscillations with a frequency appreciably lower than the frequency of the laser radiation. The observed spectrum for the plasma satellites of the Lyman Ly_α doublet of the hydrogenic F IX ion in a dense plasma was modeled theoretically. The resulting doublet profile was shown to have a complex structure that depends non-trivially both on the plasma density and on the frequency and amplitude of the plasma oscillations. The positions of the satellites and their separations allowed them to be associated with intense electrostatic oscillations with an amplitude of (4–6)×10⁸Vcm^?1 and a frequency near (0.7–1)×10¹⁵s^?1. Assuming the oscillation frequency to be determined by the strength of the magnetic field B generated in the plasma, we obtained an estimate of B that is in reasonable agreement with other measurements and estimates of this quantity. Our theoretical analysis allowed explanation of the emission spectra observed when flat fluoroplastic targets were heated by intense picosecond laser pulses.     

Picosecond characteristics of a spectrograph measured by a streak camera/video readout system

Temporal broadening of an ultrafast laser pulse upon passage through a low and high resolution spectrograph has been measured using a streak camera/video readout system.     

Effective temperature and the directional motion of fast ions in a picosecond laser plasma

Experimental data are reported on the generation of fast ions in a picosecond laser plasma at a laser-radiation intensity of 2 × 10¹⁸ W/cm². The results are obtained by measuring the Doppler spectra of hydrogen-like fluorine ions. An important feature of the energy distribution of fast ions is a slow decrease up to an energy of 1.4 MeV. In addition, the directional motion of fast ions deep into a target is found due to the redshift of the Doppler profile of the Ly _α line. The parameters of the energy distribution of the ions are theoretically estimated.     

Self-starting mode-locked picosecond Ti：sapphire laser by using of a fast SESAM

A stable continuous wave mode-locked picosecond Ti:sapphire laser by using a fast semiconductor saturable absorber mirror (SESAM) is demonstrated. The laser delivers pulse width of 20 ps at a central wavelength of 813 nm and a repetition rate of 100 MHz. The maximum output power is 1.34 W with pump power of 7 W which corresponds to an optical--optical conversion efficiency of 19.1%.     

Temporally and spectrally resolved sampling imaging with a specially designed streak camera

We present a novel sampling imaging technique capable of performing simultaneous two-dimensional measurements of the temporal and spectral characteristics of light-emission processes by use of a specially designed streak camera. A proof-of-principle experiment was performed with a homemade multifocal multiphoton fluorescence microscope. The system was calibrated with a Fabry-Perot etalon and a standard fluorophore solution (rhodamine 6G in ethanol) and was shown to have temporal and spectral resolution of 6.5 ps and 3 nm, respectively, as well as high accuracy and reproducibility in lifetime and spectrum measurement. Temporally and spectrally resolved images of 4 x 4 foci on the sample can be obtained with a snapshot.     

Laser system based on a picosecond dye laser with combined feedback for spectroscopy

A laser system comprising a synchronously pumped picosecond dye laser with combined cavity-distributed feedback and a two-stage dye amplifier is described. The dependence of the laser pulse duration on the detuning of the cavity length, the pumping level of the active medium, and the pulse number in the pulse train was investigated. It is shown that the combination of the two types of feedback provides more than ten-fold shortening of the dye laser ultrashort pulse duration. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 47–55, January–February, 1998.     

Fluorescence lifetime system for microscopy and multiwell plate imaging with a blue picosecond diode laser

We report a wide-field fluorescence lifetime imaging (FLIM) system that uses a blue picosecond pulsed diode laser as the excitation source. This represents a significant miniaturization and simplification compared with other time-domain FLIM instruments that should accelerate the development of clinical and real-world applications of FLIM. We have demonstrated this instrument in two configurations: a macroimaging setup applied to multiwell plate assays of chemically and biologically interesting fluorophores and a microscope system that has been applied to imaging of tissue sections. The importance of the adjustable repetition rate of this laser source is discussed with respect to noise reduction and precision in the lifetime determination, illustrating a further significant advantage over conventional mode-locked solid-state lasers.     

Setup and performance of a streak camera apparatus for transient absorption measurements in the ns to ms range

We describe the setup and performance of an apparatus for simultaneous time- and spectrally resolved measurements of transient absorption. The key component in this apparatus is a streak camera, yielding, for every excitation of the sample, a two-dimensional data array with 512 × 512 data points. The apparatus covers the spectral range 350–750 nm and time windows ranging from 500 ns up to 10 ms. Due to the large dynamic range of the streak camera of 10,000:1 we obtain a multiplex factor of more than 100 compared with sequential measurements at individual wavelengths. This makes it possible to extract the maximum amount of information from small amounts of sample, e.g. light-sensitive proteins. We show that already a single pump probe pulse sequence can yield useful spectra in a 20-μs time range, and that 10 pump-probe pulse sequences yield good time constants from a global lifetime analysis. An iterative method is presented for the treatment of artifacts due to scattered excitation laser light or strong fluorescence. As an alternative to a global lifetime analysis we propose a maximum entropy-based inverse Laplace transform for analysis of the data. This results in a wavelength-dependent distribution of amplitudes p(k, λ) for all rate constants k accessible with a given time window. This analysis is model free and yields a direct visual evaluation of the uncertainties in the rate constants.