Phase Of Ultrashort Optical Pulses Research Articles

Single-shot interferometric measurement of pulse-to-pulse stability of absolute phase using a time-stretch technique.

Measurement of the absolute phase of ultrashort optical pulses in real-time is crucial for various applications, including frequency comb and high-field physics. Modern single-shot techniques, such as dispersive Fourier transform and time-lens, make it possible to investigate non-repetitive spectral dynamics of ultrashort pulses yet do not provide the information on absolute phase. In this work, we demonstrate a novel approach to characterise single-shot pulse-to-pulse stability of the absolute phase with the acquisition rate of 15 MHz. The acquisition rate, limited by the repetition rate of the used free-running mode-locked Erbium-doped fibre laser, substantially exceeds one of the traditional techniques. The method is based on the time-stretch technique. It exploits a simple all-fibre Mach-Zehnder interferometric setup with a remarkable resolution of ∼7.3 mrad. Using the proposed method, we observed phase oscillations in the output pulses governed by fluctuations in the pulse intensity due to Kerr-induced self-phase modulation at frequencies peaked at 4.6 kHz. As a proof-of-concept application of the demonstrated interferometric methodology, we evaluated phase behaviour during vibration exposure on the laser platform. The results propose a new view on the phase measurements that provide a novel avenue for numerous sensing applications with MHz data frequencies.

Design and calibration of zero-additional-phase SPIDER

Zero-additional-phase spectral phase interferometry for direct electric field reconstruction (ZAP-SPIDER) is a novel technique for measuring the temporal shape and phase of ultrashort optical pulses directly at the interaction point of a spectroscopic experiment. The scheme is suitable for an extremely wide wavelength region from the ultraviolet to the near infrared. We present a comprehensive description of the experimental setup and design guidelines to effectively apply the technique to various wavelengths and pulse durations. The calibration of the setup and procedures to check the consistency of the measurement are discussed in detail. We show experimental data for various center wavelengths and pulse durations down to 7 fs to verify the applicability to a wide range of pulse parameters.

Zero-additional-phase SPIDER: full characterization of visible and sub-20-fs ultraviolet pulses

We demonstrate a novel spectral-shearing interferometry setup for characterizing the temporal amplitude and phase of ultrashort optical pulses over an extremely wide wavelength region. By the mixing of two strongly chirped auxiliary pulses with the pulse to be characterized, two spectrally sheared replicas are generated, and their spectral interference is evaluated. We fully characterize 10-fs pulses in the visible region by sum-frequency mixing and 19-fs pulses in the ultraviolet region by difference-frequency mixing. The scheme is self-referencing and highly sensitive. The zero-additional-phase scheme does not alter the unknown pulses and yields the pulse shape at the interaction point of a spectroscopic experiment.

Real-time intuitive spectrogram measurement of ultrashort optical pulses using two-photon absorption in a semiconductor

Real-time acquisition of intuitive spectrograms based on twophoton absorption frequency-resolved optical gating is demonstrated in a wavelength range around 1500 nm using an InP crystal for a two-photon absorption medium. Rapid wavelength-delay scanning, based on a counterrotating spectrometer mirror synchronized with a delay stage, is introduced and incorporated with lock-in detection for the real-time spectrogram acquisition. It is shown that the frequency marginal and average delay time of acquired spectrograms provide the spectral intensity and group delay time of optical pulses under test. This allows the direct and rapid measurement of the magnitude and phase of ultrashort optical pulses in the spectral domain without using pulse retrieval algorithms to reconstruct the pulse shapes.

Pulse characterisation of a quantum-well mode-locked laser diode by two-photon absorption frequency-resolved optical gating

The intensity and phase of ultrashort optical pulses from a 40-GHz monolithic InGaAsP quantum-well heterostructure laser diode are retrieved for the first time from two-photon absorption pulse spectrograms. The pulse traces showing the mode-locked pulses from the laser are distorted due to ultrafast absorption saturation associated with quantum-confined Stark excitons. It is suggested from comparison between experimental time-integrated spectrum and reconstructed pulse spectrum that the mode-locked pulses are formed only from a part of the longitudinal modes in the laser cavity.

Self-referencing spectral interferometry for measuring ultrashort optical pulses

This paper describes a novel self-referencing interferometric method for measuring the time-dependent intensity and phase of ultrashort optical pulses. The technique, spectral phase interferometry for direct electric-field reconstruction (SPIDER), measures the interference between a pair of spectrally sheared replicas of the input pulse. Direct (noniterative) inversion of the interferogram yields the electric field of the input pulse without ambiguity. The interferogram, which is solely a function of frequency, is resolved with a spectrometer and recorded with a slow detector. Moreover, the geometry is entirely collinear and requires no moving components. This paper describes in detail the principle of operation, apparatus, and calibration of SPIDER and gives experimental examples of reconstructed pulses.

Spectral phase interferometry for direct electric-field reconstruction of ultrashort optical pulses

We present a novel, self-referencing interferometric technique for measuring the amplitude and the phase of ultrashort optical pulses. The apparatus uses a collinear geometry that requires no moving components. The phase-retrieval procedure is noniterative and rapid and uses only two one-dimensional Fourier transforms. We apply the technique to characterize ultrashort pulses from a mode-locked Ti:sapphire oscillator.

A simple method for the determination of the intensity and phase of ultrashort optical pulses

We describe a method for determining the phase and intensity of ultrashort optical pulses in a single laser shot by analysis of the pulse spectrum after passage through a nonlinear Kerr medium. A demonstration is given using the output of a Ti: sapphire oscillator-amplifier chain.

Improved ultrashort pulse-retrieval algorithm for frequency-resolved optical gating

We report on significant improvements in the pulse-retrieval algorithm used to reconstruct the amplitude and the phase of ultrashort optical pulses from the experimental frequency-resolved optical gating trace data in the polarization-gate geometry. These improvements involve the use of an intensity constraint, an overcorrection technique, and a multidimensional minimization scheme. While the previously published, basic algorithm converged for most common ultrashort pulses, it failed to retrieve pulses with significant intensity substructure. The improved composite algorithm successfully converges for such pulses. It can now retrieve essentially all pulses of practical interest. We present examples of complex waveforms that were retrieved by the improved algorithm.

Analysis of ultrashort pulse-shape measurement using linear interferometers

A general interferometer composed of linear filters (both time stationary and frequency stationary) and a square-law detector is analyzed, and the possibilities for measuring the spectral phase of ultrashort optical pulses are enumerated. It is found that with purely time-stationary filters the phase spectrum cannot be determined with an integrating detector but that a detector with a finite bandwidth permits such a determination. It is also shown that the phase may be measured with a time-nonstationary filter and an integrating detector. The possibilities for realizing the system are evaluated.