Increased-bandwidth in ultrashort-pulse measurement using an angle-dithered nonlinear-optical crystal

Abstract

We show that the usual phase-matching-bandwidth constraint in ultrashort-laser-pulse measurement techniques is overly restrictive. Specifically, the phase-matching bandwidth need not exceed the pulse bandwidth on every pulse. Instead, only the phase-matching bandwidth integrated over the measurement period need exceed the pulse bandwidth. We show that angle-dithering a second-harmonic-generation crystal that is otherwise too narrowband (that is, too thick) can yield sufficient phase-matching bandwidth and an accurate pulse measurement. We apply this technique to frequency-resolved optical gating (FROG) and show that accurate pulse measurements can be made using a comparatively very thick and hence narrowband crystal. An additional advantage of using a thick crystal is increased signal strength.

Ultrashort pulse capability at the L2I high intensity laser facility

“…To overcome phase matching limitations, crystal dithering must be used [16] . The full spectrum was then retrieved using commercial software, resulting in a usable region extending from 650 to 1000 nm [11] .…”

Ultrashort Pulse Characterization

“…The bandwidth that can be measured (and therefore the minimum pulse duration) is limited by the range of angles traversing the crystal. This can be increased to enable measurement of 10-20 fs pulses by angle dithering the crystal or tight focusing [74,75]. In addition to simplifying the device, GRENOUILLE enables the measurement of first-order space-time coupling (i.e., angular dispersion and spatial chirp) [76,77].…”

Characterization of Supercontinuum and Ultraviolet Pulses by Using XFROG

“…However, the SFG signal is proportional to the square of the crystal thickness and a thin crystal generates a very weak signal resulting in a very low sensitivity. P. O'Shea et al proposed a novel idea that the phase matching bandwidth could be increased by using an angle-dithered, relatively thick, and hence narrowband crystal [13]. The key point was that the phase matching bandwidth doesn't need to exceed the pulse bandwidth for each pulse in a multi-shot measurement.…”