High-order nonlinear phase shift caused by cascaded third-order processes

We show, for the first time to our knowledge, that the fundamental beam that participates in the process of third-harmonic generation experiences an additional high-order nonlinear phase shift. The magnitude of the shift is proportional to the square of the pump intensity and the length of the sample and depends on the deviation from the exact phase-matched condition. This phase shift arises from cascaded third-order processes. Its value can exceed the value of the phase shift that originates from inherent fifth-order susceptibility of the nonlinear medium. Its sign is controllable by the sign of the phase mismatch of the third-harmonic generation process.     

Carrier-envelope phase of ultrashort pulsed Laguerre-Gaussian beam

The carrier-envelope phase of the ultrashort pulsed Laguerre-Gaussian beam is studied.The order of Laguerre function affects seriously the variations of the carrier-envelope phase with the propagation distance increasing.The beam waist also affects the carrier-envelope phase in a few Rayleigh distances.The variation of the carrier-envelope phase is larger on the axis than on the beam periphery in propagation.     

Carrier-envelope phase slip of ultrashort dispersion-managed solitons

The carrier-envelope phase slip of an ultrashort pulse circulating in a mode-locked Ti:sapphire laser is analyzed. The laser cavity is modeled by a dispersion- and nonlinearity-managed nonlinear Schr?dinger equation. The combined contributions to the phase slip induced by nonlinear phase and nonlinear dispersion are found to approach zero for strong dispersion maps. The dependence of the slip on third-order dispersion is found as well. The analytical results are verified using numerical simulations.     

One-step phase shift 3-D surface profilometry with grating projection

A 3-D profiling system has been developed using a grating projection approach and a one-step phase shift algorithm. In the system, a grating pattern projected on an object surface is acquired by a CCD camera, and the grating's phase deformation caused by the surface shape is extracted by spatial phase shift processing, which uses only one frame of digital image. One phase value can be calculated from a successive 3-pixel range if the fringe period is set to either 4-pixel width or 8-pixel width. The fixed phase distribution of the system is excluded by a standard plane calibration. With 8-bit input data, the system's RMS phase accuracy is developed up to 2π/60 in the experimental examinations.     

Carrier-envelope phase measurement using a non phase stable laser

We demonstrate that the phase between the carrier and the pulse envelope of a few-cycle laser pulse can be retrieved from non phase stable laser systems, provided that such laser pulses are about 5 fs long and the repetition rate is in the order of 1 kHz. Our approach is based on online determination of the phase using f-2f interferometry. By a comparison of the self referencing interferometric signal with the photoelectron current emitted into a 7 degree solid angle parallel to the laser polarization, we obtain the absolute value of the carrier envelope phase. This is provided that a Coulomb correction for electron energies below 10 eV can be correctly taken into account. PACS 42.50.Hz; 42.65.Re; 32.80.Rm     

Carrier-envelope phase effects on high-harmonic generation driven by mid-infrared laser field

The influence of the carrier-envelope phase on high-harmonic generation is investigated, both experimentally and theoretically, for three different interaction gas media, driven by mid-infrared, few-cycle and CEP-stabiUzed laser pulses. Different patterns of harmonic spectra with varying CEP for the three interaction gas media are observed. Furthermore, in comparing our experiment results to the previous works driven by near-infrared laser pulses, different phenomena are found. Through numerical simulation, we find that for the two different kinds of driving fields, i.e. mid-infrared and near-infrared laser pulses, different kinds of electron trajectories contribute to the generation of high harmonics.     

Carrier-envelope phase measurement by all-optical poling with a polar side-chain polymer

Dependence of all-optical poling efficiency on carrier-envelope phase (CEP) could be measured using photoisomerization of dye molecules which are covalently bound to a polymer main chain and have large difference in static dipole moment between the ground state and excited state. Increased chromophore density leads to an order of magnitude reduction in signal-detection time from a dye doped polymer. Analysis of all-optical poling experiments with CEP changes clearly showed the presence of polarization restoring force to zero polarization. This enables resetting of SH activity in the all-optical poling process to be used for fast response loop of CEP stabilization. Phenomenological model could explain well the difference in the growth-and-decay dynamics of poling between sample of dye doped in polymer studied previously and that grafted to a polymer main chain used in the present paper.     

An interferometric phase shift fiber Bragg grating sensing system with greatly reduced background phase noise

We presented an interferometric phase shift fiber Bragg grating(FBG) sensor, which inherited the advantages of FBG sensors, and, at the same time, the greatly reduced full-width-at-half-maximum bandwidth brought longer coherent length, higher sensitivity, and lower phase noise. Experiments show that at least a 7 dB reduction of phase noise can be achieved compared to FBG sensors interrogated by interferometer with the same optical path difference.     

The phase shift method applied to cross grating moiré measurements

The automatic evaluation of the grating deformation in a moiré image is greatly enhanced by the phase shift method. Based on three or more local grey values of a related number of phase shifted moiré patterns, the local displacement of a deformed grating against a reference grating, and hence the total displacement in one direction, is calculated. In this paper an extension to cross gratings is presented yielding a two- dimensional displacement field.     

Novel flat multichannel filter based on fiber Bragg grating and phase shift

In this letter, a novel optical fiber filter based on fiber Bragg grating and phase shift is proposed for wavelength-division-multiplexing (WDM) system applications. As the channel-space of the comb filter based on chirped sampled fiber Bragg grating and phase shift was not accurate and the multi-channel was unable to channel the standard frequency, we discussed and calculated the error between theory and practice which has certificated by simulation. Then a compensatory method with phase shift between the samples was proposed, and a 80-channel comb filter with accurate 50-GHz channel-spacing was simulated, which is a good foundation for fabricating comb filters with accurate transmission peak in future.     

On the anomalous behaviour of the doublet pd phase shift caused by a polarization potential

An estimate of pd scattering polarization effects is given in the framework of a simple two-particle model. The S-wave effective-range function is found to be discontinuous for energies E ∼ 2.3 keV.     

Carrier-envelope phase stabilization with sub-10 as residual timing jitter

We demonstrate carrier-envelope phase (CEP) stabilization of a mode-locked Ti:sapphire oscillator with unprecedented timing jitter of eight attoseconds. The stabilization performance is obtained by a combination of two different stabilization approaches. In a first step the drift of the CEP is stabilized with a conventional feedback loop by means of controlling the oscillator pump power with an acousto-optic modulator (AOM). In a second step we utilize a recently developed feed-forward type stabilization scheme which has a much higher control bandwith. Here an acousto-optic frequency shifter (AOFS) produces the stabilized output in the first diffraction order. Moreover, we present numerical results on the optimization of the length of the photonic crystal fiber, which is used to generate an octave-spanning spectrum, in order to optimize the sensitivity in the f-to-2f interferometers.     

小波变换提取放大超短脉冲载波-包络相位的研究

提出了一种新的超短放大脉冲的载波-包络相位还原方法,应用小波变换从超短放大脉冲的光谱拍频干涉中直接提取载波-包络相位. 消除了传统的Fourier变换方法不同宽度的滤波窗口引入不同程度的相位噪声而产生不确定性的影响,得到了更精确的载波-包络相位信息,对于近单周期超短脉冲特性测量具有重要意义. 关键词： 超短脉冲 载波-包络相位 相位还原 小波变换     

Carrier-envelope phase effects of over-saturated few-cycle laser pulses on high-order harmonic generation

We investigate theoretically the high-order harmonic generation driven by few-cycle laser pulses with intensities above the saturated intensity using the Lewenstein model. It is found that the carrier-envelope phase of the laser pulse has great influences on the coherence of the high-order harmonic spectrum in the plateau region when driven by a relatively weaker driver field in the oversaturated regime. While for a much higher intensity the coherence of the high-order harmonic spectrum is almost independent on the carrier-envelope phase.     

Carrier-envelope phase offset for pulses from a tunable optical parametric amplifier

The carrier-envelope phase (CEP) characteristics of the tunable infrared laser pulses from a noncollinear optical parametric amplifier (OPA) with passively stabilized CEP are investigated experimentally. We compare the CEP fluctuation of different wavelength outputs from the OPA which is seeded by the idler pulse of a difference frequency generation (DFG) process. It is found that when the OPA output is tuned to a longer wavelength, the CEP fluctuation becomes less sensitive to the jitter of laser intensity and the phase mismatch, and therefore more stable CEP for the longer wavelength output pulses is realized.     

飞秒钛宝石放大激光脉冲的载波包络相位测量与控制

通过对重复频率为1 kHz的放大飞秒激光脉冲的光谱干涉实验,结合傅里叶变换进行了载波包络相位漂移的实验研究.在此基础上利用锁相环反馈控制技术实现了对载波包络相位的精密锁定,锁定后的激光脉冲稳态相位均方根误差小于80mrad,锁定时间超过3h.同时在理论上分析了光谱干涉测量放大激光脉冲载波包络相位的原理,给出了光谱干涉信号与载波包络相位的关系. 关键词： 飞秒钛宝石放大器 载波包络相位 光谱干涉 超连续     

Electromagnetically induced phase grating controlled by spontaneous emission

Electromagnetically induced phase grating controlled by spontaneous emission is studied. The results show that the diffraction efficiency of phase grating is strikingly enhanced due to the existence of spontaneously generated coherence (SGC), and the diffraction efficiency of 35% can be obtained in optimal SGC parameter case. Furthermore, at large SGC parameter, the high efficiency of phase grating can be maintained by the application of weak coupled and relatively strong probe fields, and choosing the proper length of atomic sample. At the same time, in such an atomic system, the SGC effect depends on incoherent pump.     

Blind phase shift extraction and wavefront retrieval by two-frame phase-shifting interferometry with an unknown phase shift

An iterative algorithm to extract the arbitrary unknown phase shift in two-frame phase-shifting interferometry and then reconstruct the complex object wave is proposed. In combination with the least square principle and some calculation formulae we developed, this algorithm allows us to find the value of unknown phase shift by using only two interferograms without additional knowledge or measurement. Computer simulations have shown that this algorithm works well for both the smooth and diffusing objects to a very high accuracy over a wide range of the phase shift from 0.4 to 2.5 rad.     

Measurement of residual stress by phase shift shearography

This paper presents a method for evaluating residual stresses. The approach is based on measuring the deformation due to the relief of stress produced by a drilled-hole or a ball indentation, and the deformation is rapidly measured by digital shearography. This method does not require mounting strain gages/transducers. Unlike holography, shearography does not require special vibration isolation. These features make the method practical for evaluation of residual stresses in a production/field environment.