Spectral Phase Distortions Research Articles

Phase-modulated rapid-scanning fluorescence-detected two-dimensional electronic spectroscopy.

We present a rapid-scanning approach to fluorescence-detected two-dimensional electronic spectroscopy that combines acousto-optic phase-modulation with digital lock-in detection. This approach shifts the signal detection window to suppress 1/f laser noise and enables interferometric tracking of the time delays to allow for correction of spectral phase distortions and accurate phasing of the data. This use of digital lock-in detection enables acquisition of linear and nonlinear signals of interest in a single measurement. We demonstrate the method on a laser dye, measuring the linear fluorescence excitation spectrum as well as rephasing, non-rephasing, and absorptive fluorescence-detected two-dimensional electronic spectra.

Approaching the diffraction-limited, bandwidth-limited Petawatt.

J-KAREN-P is a high-power laser facility aiming at the highest beam quality and irradiance for performing state-of-the art experiments at the frontier of modern science. Here we approached the physical limits of the beam quality: diffraction limit of the focal spot and bandwidth limit of the pulse shape, removing the chromatic aberration, angular chirp, wavefront and spectral phase distortions. We performed accurate measurements of the spot and peak fluence after an f/1.3 off-axis parabolic mirror under the full amplification at the power of 0.3 PW attenuated with ten high-quality wedges, resulting in the irradiance of ~1022 W/cm2 and the Strehl ratio of ~0.5.

High-order dispersion control of 10-petawatt Ti:sapphire laser facility.

A grism pair is utilized to control the high-order dispersion of the Shanghai Superintense Ultrafast Lasers Facility, which is a large-scale project aimed at delivering 10-PW laser pulses. We briefly present the characteristics of the laser system and calculate the cumulative B-integral, which determines the nonlinear phase shift influence on material dispersion. Three parameters are selected, grism separation, angle of incidence and slant distance of grating compressor, to determine their optimal values through an iterative searching procedure. Both the numerical and experimental results confirm that the spectral phase distortion is controlled, and the recompressed pulse with a duration of 24 fs is obtained in the single-shot mode. The distributions and stabilities of the pulse duration at different positions of the recompressed beam are also investigated. This approach offers a new feasible solution for the high-order dispersion compensation of femtosecond petawatt laser systems.

Fourth-order dispersion compensation for ultra-high power femtosecond lasers

Fourier-transform-limit pulses are required by recent petawatt-class femtosecond chirped-pulse amplification lasers for increasing peak powers, but which are challenged by the residuals of the high orders of dispersion, for example the fourth-order dispersion. We propose a stable and economy passive dispersion compensation method to completely cancel out the static second-, third- and especially fourth-order dispersion by inserting a grism pair into the standard chirped-pulse amplification system between the stretcher and the compressor. The best dispersion compensation condition would be achieved by optimizing both the grism pair and the compressor. Compared with the recent passive dispersion compensation method, the experiment results show the pulse duration could be further reduced from 35fs to 28fs, the peak intensity of the compression pulse could be increased by 1.25 times, and the spectral phase distortion over the pulse spectrum could be reduced from 12rad to 4rad.

English

This paper presents an objective quality assessment for digital images that have been degraded by noise. Objective quality assessment is crucial and is generally used in image processing. The main objective of this paper is to analyse various statistical properties and their measurements and finally compare them. The statistical properties that are included are mean square error (MSE), root mean square error (RMSE), signal to noise ratio (SNRQ), peak signal to noise ratio (PSNR) and certain frequency parameters like spectral magnitude distortions and spectral phase distortions. But it is observed that MSE and PSNR yield poor results therefore a new metric namely structure similarity is proposed which has a better performance than MSE and PSNR but fails when applied on badly blurred images. Therefore, edge based structure similarity index metric (ESSIM) is proposed. Experiment results show that ESSIM is more consistent with human visual system (HVS) than SSIM and PSNR especially for the blurred images.

Wave-Breaking Extended Coherent Fiber Supercontinuum Pulse Compression

Like surface water wave breaking, optical wave breaking (WB) is a phenomenon that occurs when an optical pulse propagates in a normally dispersive nonlinear fiber. It is often avoided in fiber continuum compression experiments by using lower coupling power or shorter fiber length, because the WB-extended continuum has higher-order spectral phase distortions that cannot be compensated by a quadratic compressor, a prism pair or a grating pair. This issue can be resolved when an ideal compressor such as a 4f pulse shaper is used. Linear and nonlinear chirps can be removed by arbitrary phase shaping toward transformlimited pulse compression.

Temporal contrast degration due to spectral phase distortion in CPA lasers

We theoretically study the temporal contrast degradation by the spectral phase distortion in chirped pulse amplification (CPA) lasers. As an example, we analyze the impact of the surface qualities of the optical elements such as mirrors and grating in the stretcher and compressor on the temporal contrast. The temporal contrast declines fast in the case of a rapidly varying random surface error of the optical elements. When the values of PV, RMS and GRMS of the surface error curve are reduced, the temporal contrast is becoming better and better. And the temporal contrast can be improved after the surface error curve is to be spatial filtering. Those results are helpful for the choice of the surface parameters of the optical elements in the stretcher and compressor. OCIS codes: 140.7090, 320.5520, 320.5390. doi: 10.3788/COL201210.S21401.

Generation of sub-10 fs ultraviolet Gaussian pulses

A technique is proposed for generating sub-10fs deep ultraviolet (DUV) pulses with Gaussian temporal and spectral profiles. In this approach, a broadband DUV pulse with a negative frequency chirp is generated and compressed by normal group-velocity dispersion in a transparent medium. The pulse shape is not significantly distorted by high-order spectral phase distortion. In principle, nearly transform-limited sub-6fs UV pulses with pulse energies of several tens of microjoules are expected to be generated. Numerical simulations indicate that a Ti:sapphire chirped-pulse amplifier with a pulse energy of several millijoules and a pulse duration of 35fs can be used to generate high-energy sub-6fs UV pulses. The technique is partially demonstrated by an experiment using a low-power Ti:sapphire chirped-pulse amplifier to generate low-energy sub-10fs single DUV pulses with waveforms that quantitatively agree with those predicted by the numerical simulations. This technique can be used to generate high-energy sub-10fs DUV pulses with Gaussian temporal and spectral profiles for ultrafast spectroscopy in the gas phase as well as the liquid and solid phases.

Asynchronous encrypted information transmission with sub-6 fs laser system at 2.12 GHz repetition rate

The asynchronous transmission (encoding and decoding) of 64-bit information using binary spectral phase shaping is demonstrated. The accurate introduction and retrieval of the binary information is possible by using multiphoton intrapulse interference phase scan (MIIPS) to measure and correct the spectral phase distortions of the laser and the transmission media. Experimental demonstration is achieved using a sub-6 fs Ti:Sapphire laser with 2.12-GHz repetition rate and an adaptive phase control system.

Broadband group delay dispersion compensation for a microscope objective lens with a specially-designed mechanical deformable mirror

We propose that the bending profile of a mechanical deformable mirror can be designed by shaping its form, realizing a simple, compact, and broadband group delay dispersion compensator in a 4-f pulse shaper arrangement. By using the proposed compensator, spectral phase distortion of a microscope objective lens is successfully pre-compensated for to generate a sub-8 fs pulse at the focus of the lens.

Modified spectrum autointerferometric correlation (MOSAIC) for single-shot pulse characterization

A method for generation of the modified spectrum autointerferometric correlation that allows single-shot pulse characterization is demonstrated. A sensitive graphical representation of the ultrashort pulse phase quality is introduced that delineates the difference between the presence of temporal and spectral phase distortions. Using these schemes, full-field reconstruction of ultrashort laser pulses is obtained in real time using an efficient iterative technique.

Real-time spatial–spectral interference measurements of ultrashort optical pulses

Real-time linear spectral interference measurements of ultrashort pulses are shown experimentally. The technique involves measurements of the two-dimensional interference pattern of the spectral interference between a reference and a signal pulse propagating at an angle with respect to each other. No postprocessing is needed to extract the spectral phase difference between the two pulses. Quadratic spectral phase distortions as well as spectral phase discontinuities are measured. The method is applicable to single-shot measurements of ultraweak pulses and is useful for identification of the critical adjustments of ultrashort pulse shapers and compressors.

Evaluation and analysis of coded speech quality

AbstractRating scale data for evaluating coded speech quality by the mean opinion score (MOS) are factor‐analyzed to show the possibility of extracting rich information from them. Two factors, softness‐shrillness and clearness‐noisiness, are extracted. Factor scores expressing a kind of multidimensional scale of speech quality are related to several physical parameters of speech samples, e.g., differential spectral distortion, phase distortion, and dissonance. Individual subject differences in evaluating speech quality are extracted as the factor loadings. It is found also that speech specialists and nonspecialists place different weights on different factor axes.

Picosecond time-space holographic interferograms stored by persistent spectral hole burning

A novel approach to interferometric processing of ultrafast optical signals is demonstrated by using hologram storage in persistent spectral hole burning media. Multiple time-space holographic images of ultrafast scenes are interferometrically compared by using read-out with a frequency-tunable narrow band laser. The feasibility of simultaneous detection of spatial and spectral phase distortions of picosecond wavefronts is demonstrated.