Single-shot spectral interferometry with chirped pulses

We present a method for obtaining time-resolved measurements of the amplitude modulation and the phase shift of a chirped probe pulse interacting with a femtosecond-laser-produced plasma. Based on spectral interferometry, the technique allows for single-shot measurements and keeps the temporal resolution associated with the full bandwidth of the probe pulse. We demonstrate the efficiency of this technique by probing femtosecond-laser breakdown of plastic targets.     

Single-shot multiple-delay crossed-beam spectral interferometry for measuring extremely complex pulses

We demonstrate a single-shot measurement technique based on spectral interferometry (SI) for measuring the complete intensity and phase vs. time of extremely complex ultrashort laser pulses. Ordinarily, such a method would require an extremely-high-resolution spectrometer, but, by temporally interleaving many SI measurements, each using a different reference-pulse delay, our method overcomes this need. It involves introducing a transverse time delay into the reference pulse by tilting its pulse front transversely to the spectrometer dispersion plane. The tilted reference pulse then gates the unknown pulse by interfering with it at the image plane of a low-resolution imaging spectrometer, yielding an effective increase in the delay range and spectral resolution—by a factor of 30 in our proof-of-principle implementation. Our device achieved a temporal resolution of ~ 130 fs and a temporal range of 120 ps. This simple device has the potential to measure even longer and more complex pulses.     

Single-shot measurement of carrier-envelope phase changes by spectral interferometry

We demonstrated single-shot measurements of spectral interference between a white-light continuum generated in a hollow-fiber and its second harmonic. The interference has information on the carrier-envelope phase of an input pulse to the fiber and the time delay of the blue wing of the continuum. By analyzing the observed spectral interference, we estimated shot-by-shot changes of the carrier-envelope phase. This method is useful for determining the carrier-envelope phase changes of a low-repetition-rate, high-intensity laser.     

Analysis of extreme ultraviolet spectral profiles of laser-produced Cr plasmas

Radiation from laser-produced plasmas was examined as a potential wavelength calibration source for spectrographs in the extreme ultraviolet(EUV) region.Specifically, the EUV emission of chromium(Cr) plasmas was acquired via spatiotemporally resolved emission spectroscopy.With the aid of Cowan and flexible atomic code(FAC) structure calculations,and a comparative analysis with the simulated spectra, emission peaks in the 6.5–15.0 nm range were identified as 3 p–4 d, 5 d and 3 p–4 s transition lines from Cr~(5+)–Cr~(10+)ions.A normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model were assumed for the spectral simulations, and used to estimate the electron temperature and density in the plasma.The results indicate that several relatively isolated emission lines of highly charged ions would be useful for EUV wavelength calibration.     

Single-shot kilohertz characterization of ultrashort pulses by spectral phase interferometry for direct electric-field reconstruction

We describe a method of characterizing ultrashort optical pulses that is based on the technique of spectral phase interferometry for direct electric-field reconstruction and is capable of simultaneously measuring the amplitude and the phase of the electric field of a sub-10-fs pulse at kilohertz acquisition rates on a single-shot basis. Use of this technique results in a dramatic increase (>50x) in acquisition rate compared with that of existing diagnostics for full E-field characterization and opens the door to a range of new experiments in which shot-to-shot phase and amplitude fluctuations are studied at kilohertz rates.     

Single-shot two-dimensional spectrometer

A two-dimensional optical spectrometer is demonstrated using simple optical components. This spectrometer is based on ultrafast two-dimensional (2D) frequency-dispersed pump-probe spectroscopy and can be used for single-shot correlation spectroscopy. To demonstrate functionality of this device, we measure the 2D correlation spectrum of atomic rubidium.     

Single-shot, high-dynamic-range measurement of sub-15 fs pulses by self-referenced spectral interferometry

We explore theoretically and numerically the temporal contrast limitation of a self-referenced spectral interferometry measurement. An experimental confirmation is given by characterization and fine compression of hollow-core fiber generated sub-15 fs pulses, yielding an accurately measured coherent contrast of 50 dB on a ±400 fs time range.     

Single-shot real-time characterization of chirped-pulse amplification systems by spectral phase interferometry for direct electric-field reconstruction

We characterize chirped-pulse amplification systems by using spectral phase interferometry for direct electric-field reconstruction. For the first time to the authors' knowledge, single-shot real-time operation has been obtained for this technique, leading to a fast and accurate optimization of these systems.     

Single-shot chirped-pulse spectral interferometry used to measure the femtosecond ionization dynamics of air

A novel interferometry technique is presented by which, in one shot, one can measure phase changes with a resolution of tens of femtoseconds while extending the measurement over picoseconds or even longer. The method is based on spectral (frequency-domain) interferometry with a pair of linearly chirped pules as probes. With this technique we obtained single-shot measurements of the rapid phase changes induced by optical field ionization of air. This allowed us to calculate the time profile of the electron density created by an intense short laser pulse.     

Ionization effects in laser-produced plasmas

We describe a steady state density and temperature dependent atomic physics package TRIP (4) which we have incorporated into a 1-D lagrangian computer code MEDUSA. Using this modified version of the code we evaluate the degree of ionization and study the effect of atomic processes in laser-compression simulations of gas filled micro-balloons.     

靶的厚度对激光产生的x射线输运到靶后能谱的影响

利用一维辐射流体动力学程序MULTI数值模拟研究了功率为10¹⁴W/cm²、脉冲宽度为1ns、波长为0.35μm的短脉冲强激光辐照不同厚度的平面Au靶时，靶厚度对靶背面x射线能谱结构和辐射强度的影响. 关键词： 激光等离子体 辐射流体力学 x射线转换     

Pulsations and chaos in laser-produced plasmas

A general criterion is proposed predicting the onset of chaotic behavior for parametric processes in a laser-produced plasma. The conditions when the transition to the stochastic regime occur are determined for various parametric instabilities excited when a high intensity laser interacts with a plasma. The complicated temporal structure observed in 3/2₀, 2₀, 1₀, and fast electron emission in experiments using high-intensity (I10^15–17 W/cm²), short ( _L 40–200 psec) Nd laser pulses is attributed to the reflection seeded SBS instability being driven into this regime.Lebedev Physics Institute, Leninsky Prospect 53, Moscow 117924 Russia.     

Density scalelength estimation in laser-produced plasmas

The relative intensities of the blue- and red-shifted satellites of three-halves harmonic spectra backscattered from plasmas produced by irradiation of targets with a high power Nd laser pulse have been measured. These have been used to estimate the plasma density scalelength due to the different emergent paths of each satellite.     

Optical energy balance in laser-produced plasmas

Optical energy balance in plasmas produced by irradiating solid targets by highpower laser pulses, has been experimentally determined. The total light scattered has been measured as a function of the laser intensity and the irratiated spot diameter. It has been found that the net light absorption does not depend on the laser intensity alone, but is also affected by the irradiated spot area. It has also been observed that diffuse back reflection becomes a dominant loss mechanism at high incident flux and small irradiated spot area.     

Single-shot sonogram: a real-time chirp monitor for ultrafast oscillators

We report a static single-shot configuration for measuring the sonogram trace of an ultrashort optical pulse. When it is combined with a CCD camera, the instrument provides an intuitive video-rate monitor of the pulse chirp, and it is equally compatible with a high-repetition-rate mode-locked oscillator and a low-repetition-rate amplified source. The performance of the instrument is described, and iterative retrieval of the measured sonogram trace, which yields complete and unambiguous pulse characterization, is demonstrated.     

X-ray spectrometry of laser-produced aluminum plasmas

X-ray lines and continuum emission from a laser-produced aluminum plasma have been studied. The electron temperature variations during the laser pulse (30 ns) were deduced from time-dependent measurements of intensities of resonance lines (2.5 ns time-resolution). Comparison is made with electron temperature values deduced from ion emission measurements.     

Elliptically-bent crystal spectrograph for X-ray diagnosis of laser-produced plasmas

In order to measure spatially and temporarily resolved laser-produced plasma X-ray spectra in 0.2 - 2nm region, a novel two-channel elliptically-bent crystal spectrograph has been developed. Dispersive elements are LiF, PET, Mica, and KAP crystals, which cover Bragg angles in the range of 30 - 67.5degrees. Eccentricity and focal distance of twin ellipses are 0.9586 and 1350 mm, respectively. Spatially resolved spectrum is photographically recorded with an X-ray film or X-CCD camera in one channel, and temporarily resolved one is photographically recorded with an X-ray streak camera in another channel,thus spatially and temporarily resolved spectra can be simultaneously obtained. Spectral images were acquired with X-CCD and PET in SHENGUANG-Ⅱ laser facility, and experimental results show that the spectral resolution of the spectrograph is about 0.002 nm.