Dongjoo Lee

Describing first-order spatio-temporal distortions in ultrashort pulses using normalized parameters.

We develop a first-order description of spatio-temporal distortions in ultrashort pulses using normalized parameters that allow for a direct assessment of their severity, and we give intuitive pictures of pulses with different amounts of the various distortions. Also, we provide an experimental example of the use of these parameters in the case of spatial chirp monitored in real-time during the alignment of an amplified laser system.

Toward single-shot measurement of a broadband ultrafast continuum

We discuss the problem of measuring the intensity and phase of a broadband continuum in a single shot, considering three possible methods, and perform preliminary measurements using one of them. Our measurements use transient-grating cross-correlation frequency-resolved optical gating (TG XFROG) with a third-order nonlinear medium, which currently can phase match over 300 nm simultaneously. We demonstrate this technique for a continuum generated in bulk fused silica that is 12.5 mm thick. Due to limited reference-pulse energy, we do not achieve a true single-shot measurement, instead averaging over approximately five shots. The retrieved trace and spectrum contain fine structure, and the retrieved temporal phase is mainly quadratic.

Experimentally simple, extremely broadband transient-grating frequency-resolved-opticalgating arrangement.

We demonstrate a simple, essentially alignment-free Transient-Grating Frequency-Resolved-Optical-Gating arrangement using a simple input mask that separates the input beam into three beams and a Fresnel biprism that crosses and delays them. It naturally operates single shot and has no moving parts. It is also extremely broadband and hence should be ideal for measuring pulses from optical parametric amplifiers.

Effect—and removal—of an ultrashort pulse's spatial profile on the single-shot measurement of its temporal profile

Because single-shot ultrashort-pulse-measurement methods usually map delay onto the transverse spatial coordinate, a nonuniform pulse spatial profile could badly distort the measurement versus delay. Furthermore, beam-induced distortions could occur in techniques, such as GRENOUILLE, in which the pulse frequency is mapped to the angular coordinate in the orthogonal direction. We study these effects in the frequency-resolved-optical-gating (FROG) and GRENOUILLE techniques and show that they are considerably reduced by fortuitous aspects of, in particular, the GRENOUILLE beam geometry in practice. Also, we show that it is possible to remove both of these distortion effects by simply dividing the trace by a simple function of the beam input spatial profile. We demonstrate these (small) effects and their removal in GRENOUILLE measurements.

Extremely simple device for measuring ultrashort pulses in the visible

We demonstrate an extremely simple frequency-resolved-optical-gating device (GRENOUILLE) ideal for measuring visible ultrashort pulses. By angle-tuning a thick crystal, its range includes almost the entire visible spectrum.

Highly simplified device for measuring the intensity and phase of picosecond pulses

We demonstrate an extremely simple frequency-resolved-optical-gating (GRENOUILLE) device for measuring the intensity and phase of relatively long-ps-pulses. In order to achieve the required high spectral resolution and large temporal range, it uses a few-cm-thick second-harmonic-generation crystal in the shape of a pentagon. This has the additional advantage of reducing the devices total number of components to as few as three simple easily aligned optics, making it the simplest device ever developed for complete pulse measurement. We report complete intensity-and-phase measurements of pulses up to 15ps long with a time-bandwidth product of 21.

Measuring complex and visible ultrashort pulses

Frequency-Resolved Optical Gating (FROG) and its variations are the only techniques available for measuring complex pulses without a well-characterized reference pulse. We study the performance of the FROG generalized-projections (GP) algorithm for retrieving the intensity and phase of very complex ultrashort laser pulses in the presence of noise. Also, we show that a highly simplified version of FROG, GRENOUILLE, can easily measure visible pulses. By tuning a thick crystal, it can cover the entire visible spectrum, which is typically generated from commercial Optical Parameter Amplifications (OPAs)

Measuring Complex and Visible Ultrashort Pulses

We show that frequency-resolved optical gating (FROG) can reliably measure extremely complex pulses and that a highly simplified version of it (GRENOUILLE) can easily measure visible pulses.

Simple Device for Measuring Ultrashort Pulses in the Visible

We demonstrate an extremely simple frequency-resolved-optical-gating (FROG) device (GRENOUILLE) ideal for measuring visible ultrashort pulses. By angle-tuning a thick crystal, its range includes almost the entire visible spectrum.

The effect (or lack of it) of an ultrashort pulse’s spatial profile on the single-shot measurement of its temporal profile

A non-uniform spatial profile could distort single-shot pulse measurements. But, surprisingly, we show that these effects are significantly reduced by several fortuitous aspects of the GRENOUILLE technique and so usually have little effect in practice.