Phase Of Ultrashort Pulses Research Articles

All-reflective self-referenced spectral interferometry for single-shot measurement of few-cycle femtosecond pulses in a broadband spectral range

An all-reflective self-referenced spectral interferometry based on the transient grating (TG) effect is proposed for single-shot measuring of the amplitude and phase of ultrashort pulses in a broadband spectral range. Except for a thin third-order nonlinear medium, which was used to generate the TG signal, no transmitted optics were used in the proposed device, and few-cycle pulses in a broad spectral range from deep UV to mid-IR can be characterized. With a homemade compact and alignment-free device, a 5.0 fs pulse at 800 nm corresponding to about two cycles and a 14.3 fs pulse at 1800 nm corresponding to less than three cycles were successfully characterized.

Shaper-based approach to real-time correction of ultrashort pulse phase drifts and transient pulse dispersion measurements

We demonstrate for the first time active dispersion and amplitude correction in a fiber laser producing sub-45 fs pulses. The approach is based on single-shot second and third order dispersion measurement based on multiphoton intrapulse interference. The same principle is applied to obtain time-resolved measurements of the transient dispersion induced by an intense laser pulse on a silica window.

Recent progress and future prospects of high-energy peta-watt laser in LFRC, CAEP

The laser system with output energy larger than 150 Joules, output pulse width less than 1-ps has been finished in last year in Research Center of Laser Fusion (LFRC) at China Academy of Engineering Physics (CAEP). The front-end of the system can emit 4-mJ, 1053-nm femtosecond laser by optical parametric amplification based on supercontinuum white-light injection. Then the laser is stretched to chirped pulse with 2ns pulse duration and amplified to near 200 Joules by multi-stage phosphate Nd:glass amplifiers. Subsequent amplification in a chirped-pulse amplification (CPA) chain will result in a sometimes substantial lengthening of the output pulses owing to gain narrowing and uncompensated phase errors. The acousto-optic programmable dispersive filter (AOPDF) [2] is used to modulate the amplitude and phase of ultrashort pulses in order to maintain the short pulse duration after amplification. The size of a single gratings is not enough for high energy pulse compression, Therefore we developed tiled-gratings technology. A single-pass tiled-gratings-compressor (TGC) [3] is used in this system. Real-time monitoring and on-line alignment system has been established to achieve coherent addition of the tiled gratings. Impact of vibration being eliminated to a least level, the tiled gratings can keep stable for a several hours.

Full-field characterization of femtosecond pulses by spectrum and cross-correlation measurements: addenda

We present a practical and accurate technique for retrieving the amplitude and the phase of ultrashort pulses from a nonlinear (second-order) intensity cross correlation and the spectrum that overcomes shortcomings of previous attempts. We apply the algorithm to theoretical and experimental data and compare it with frequency-resolved optical gating.

Full-field characterization of femtosecond pulses by spectrum and cross-correlation measurements

We present a practical and accurate technique for retrieving the amplitude and the phase of ultrashort pulses from a nonlinear (second-order) intensity cross correlation and the spectrum that overcomes shortcomings of previous attempts. We apply the algorithm to theoretical and experimental data and compare it with frequency-resolved optical gating.

New approach to determine the intensity and phase of ultrashort pulses by use of time-to-space conversion and a noniterative phase-retrieval algorithm

We propose a novel scheme for directly determining the intensity and phase of ultrashort pulses. The technique involves time-to-space conversion of an input pulse by a diffraction grating, followed by the detection of its spectral intensity distributions in the Fourier transform plane with and without an exponential filter placed in front of the grating. By use of an efficient noniterative phase-retrieval algorithm, the spectral phase of the pulse is retrieved from these spectral intensities. The intensity and phase of the pulse in the temporal domain can be reconstructed by the inverse Fourier transformation of the retrieved spectral amplitude. Computer simulation results confirm that robust reconstructions of a linearly chirped pulse and a pulse with quadratic and cubic spectral phases are possible with high fidelity.

Complete characterization of a self-mode-locked Ti:sapphire laser in the vicinity of zero group-delay dispersion by frequency-resolved optical gating

The intensity and the phase of ultrashort pulses from a self-mode-locked Ti:sapphire laser operating in the vicinity of zero group-delay dispersion (GDD) have been completely characterized by the technique of frequency-resolved optical gating (FROG). For small values of negative GDD, the appearance of a dispersive wave in the pulse spectrum is manifested in the measured FROG trace, and pulse retrieval directly shows its association with a broad leading-edge pedestal. For positive GDD, we confirm previous experimental observations of picosecond pulses with large positive chirp and report a new operating regime in which the output pulses are of picosecond duration but are intensity modulated at 20 THz. The physical origin of this modulation is discussed by analogy with similar effects observed during pulse propagation in optical fibers, and the experimental results are compared with a model of intracavity four-wave mixing about the cavity zero GDD wavelength.

Evolving FROGS:?phase retrieval from frequency-resolved optical gating measurements by use of genetic algorithms

We present a new technique based on genetic algorithms for retrieving the electric field and the phase of ultrashort pulses from frequency-resolved optical gating (FROG) traces. We have successfully applied a very basic genetic algorithm to the two most common beam geometries: polarization gate and second-harmonic generation (SHG). In the case of SHG FROG, the genetic algorithm returns a lower error than the standard iterative composite algorithm.

Quantitative investigation of optical phase-measuring techniques for ultrashort pulse lasers

We have performed a quantitative investigation into the capabilities and the limitations of two phase-measuring techniques: second-harmonic-generation frequency-resolved optical gating and direct optical spectral phase measurement. In particular, we have studied the reproducibility and the accuracy of these techniques in measuring the frequency-dependent phase of ultrashort pulses with varying amounts of cubic and quadratic phase. We find that both of these techniques are accurate to within 5% in measuring phase distortions in optical pulses.

Ultrashort optical waveform measurements using frequency-resolved optical gating

We measure the intensity and phase of ultrashort pulses from a self-mode-locked Ti:sapphire laser using the recently developed technique of frequency-resolved optical gating. These results represent to our knowledge the shortest complete optical waveform characterization measurements performed to date. We also verify recent theoretical calculations that predict that the main limitation on the pulse duration from these lasers is the presence of uncompensated higher-order dispersion.

Using phase retrieval to measure the intensity and phase of ultrashort pulses: frequency-resolved optical gating

We recently introduced a new technique, frequency-resolved optical gating (FROG), for directly determining the full intensity I(t) and phase φ(t) of a single femtosecond pulse. By using almost any instantaneous nonlinear-optical interaction of two replicas of the ultrashort pulse to be measured, FROG involves measuring the spectrum of the signal pulse as a function of the delay between the replicas. The resulting trace of intensity versus frequency and delay yields an intuitive display of the pulse that is similar to the pulse spectrogram, except that the gate is a function of the pulse to be measured. The problem of inverting the FROG trace to obtain the pulse intensity and phase can also be considered a complex two-dimensional phase-retrieval problem. As a result, the FROG trace yields, in principle, an essentially unique pulse intensity and phase. We show that this is also the case in practice. We present an iterative-Fourier-transform algorithm for inverting the FROG trace. The algorithm is unusual in its use of a novel constraint: the mathematical form of the signal field. Without the use of a support constraint, the algorithm performs quite well in practice, even for pulses with serious phase distortions and for experimental data with noise, although it occasionally stagnates when pulses with large intensity fluctuations are used.

Amplitude and phase recording of ultrashort pulses

The performance of a new method of measuring the amplitude and phase of ultrashort pulses is evaluated with simulated and real data.