Daniel J. Kane

Real-time measurement of ultrashort laser pulses using principal component generalized projections

Frequency-resolved optical gating (FROG) is a technique to measure ultrashort laser pulses that optically constructs a spectrogram of a laser pulse. A two-dimensional (2-D) phase retrieval algorithm is used to extract the intensity and phase of a pulse from its spectrogram. We have improved a recently presented principal component generalized projections algorithm (PCGPA) making it easier to implement and fast enough to allow real-time inversion of FROG spectrograms. A femtosecond oscilloscope, based on second-harmonic generation (SHG) FROG, that displays the intensity and phase of ultrashort laser pulses in real time utilizing the improved PCGP phase retrieval algorithm is presented.

Spectral encoding method for measuring the relative arrival time between x-ray/optical pulses

The advent of few femtosecond x-ray light sources brings promise of x-ray/optical pump-probe experiments that can measure chemical and structural changes in the 10-100 fs time regime. Widely distributed timing systems used at x-ray Free-Electron Laser facilities are typically limited to above 50 fs fwhm jitter in active x-ray/optical synchronization. The approach of single-shot timing measurements is used to sort results in the event processing stage. This has seen wide use to accommodate the insufficient precision of active stabilization schemes. In this article, we review the current technique for measure-and-sort at the Linac Coherent Light Source at the SLAC National Accelerator Laboratory. The relative arrival time between an x-ray pulse and an optical pulse is measured near the experimental interaction region as a spectrally encoded cross-correlation signal. The cross-correlation provides a time-stamp for filter-and-sort algorithms used for real-time sorting. Sub-10 fs rms resolution is common in this technique, placing timing precision at the same scale as the duration of the shortest achievable x-ray pulses.

Modeling and Direct Electric-Field Measurements of Passively Mode-Locked Quantum-Dot Lasers

A delay differential equation model of a passively mode-locked two-section quantum-dot laser reveals pulse asymmetry that is experimentally confirmed through direct electric-field measurements using frequency-resolved optical gating. This finding indicates that conventional autocorrelators, which obscure the underlying pulse structure due to the symmetry inherent in autocorrelation, are of limited utility in the characterization of these lasers.

Characteristics and instabilities of mode-locked quantum-dot diode lasers.

Passively mode-locked quantum-dot diode lasers are very difficult to characterize because they are typically unstable, have low peak powers, and high bandwidth. Measure data indicates these lasers are not typically mode-locked.

Spectral encoding based measurement of x-ray/optical relative delay to ~10 fs rms

A recently demonstrated single-shot measurement of the relative delay between x-ray FEL pulses and optical laser pulses has now been improved to ~10 fs rms error and has successfully been demonstrated for both soft and hard x-ray pulses. It is based on x-ray induced step-like reduction in optical transmissivity of a semiconductor membrane (Si3N4). The transmissivity is probed by an optical continuum spanning 450 - 650 nm where spectral chirp provides a mapping of the step in spectrum to the arrival time of the x-ray pulse relative to the optical laser system.

Imaging by integrating stitched spectrograms

A new diffractive imaging technique named Imaging By Integrating Stitched Spectrograms (IBISS) is presented. The technique is successfully demonstrated using a Helium Neon laser to image a 350-μm wide sample with 12μm resolution.

Pulse characterization of a passively mode-locked quantum dot semiconductor laser using FROG and autocorrelation

A comparison between the operational map of a QD MLL done by autocorrelation and FROG is made. The results show that the complete mode-locking region is significantly smaller when FROG is used versus autocorrelation.

Pulse characteristics of passively mode-locked quantum dot lasers

Interest in quantum dot mode-locked lasers (QD MLLs) has grown in recent years since their first demonstration in 2001 as applications for optical time domain multiplexing, arbitrary waveform generation, and optical clocking are anticipated. Ultrafast pulses below 1 ps have been reported from QD MLLs using intensity autocorrelation techniques, but so far detailed characterization examining the pulse shape, duration, chirp, and degree of coherence spiking in these lasers has not been carried out. We describe the first direct frequency-resolved optical gating (FROG) measurements on a QD MLL operating at a repetition rate of 5 GHz.

Modeling and direct electric-field measurements of passively mode-locked quantum-dot lasers

A delay-differential equation model of a passively mode-locked quantum-dot laser reveals pulse asymmetry that is experimentally confirmed through direct electric-field measurements. This finding implies conventional autocorrelators obscure the underlying pulse structure.

Imaging by Integrating Stitched Spectrograms

A new diffractive imaging technique named Imaging By Integrating Stitched Spectrograms (IBISS) is presented. The technique is successfully demonstrated using a Helium Neon laser to image a 350-μm wide sample with 12μm resolution.