Pulse front adaptive optics: a new method for control of ultrashort laser pulses

Abstract

Ultrafast lasers enable a wide range of physics research and the manipulation of short pulses is a critical part of the ultrafast tool kit. Current methods of laser pulse shaping are usually considered separately in either the spatial or the temporal domain, but laser pulses are complex entities existing in four dimensions, so full freedom of manipulation requires advanced forms of spatiotemporal control. We demonstrate through a combination of adaptable diffractive and reflective optical elements - a liquid crystal spatial light modulator (SLM) and a deformable mirror (DM) - decoupled spatial control over the pulse front (temporal group delay) and phase front of an ultra-short pulse was enabled. Pulse front modulation was confirmed through autocorrelation measurements. This new adaptive optics technique, for the first time enabling in principle arbitrary shaping of the pulse front, promises to offer a further level of control for ultrafast lasers.

Pulse front adaptive optics in multiphoton microscopy

“…3 A reflective element such as a deformable mirror (DM) alters both phase and pulse front for the incident beam, while a diffractive element such as a liquid crystal spatial light modulator (SLM) alters only the phase front. Hence it is possible to decouple the pulse and phase front for the beam and generate various pulse front shapes whilst maintaining a flat phase front.…”

“…By appropriately driving two AOEs (one refractive and the other diffractive) in tandem one can control the pulse front without distorting the phase front of the beam. 3 Here, we elaborate on recent work 4 in applying this concept to correction of pulse front distortion in a two-photon microscope.…”

Pulse front adaptive optics in two-photon microscopy

“…In applications such as optical microscopy and laser material processing, the system resolution and efficiency have been greatly improved by the correction of phase aberrations [1,2]. Going beyond phase front control, we recently introduced an adaptive optics concept that is able to arbitrarily shape the pulse front of ultrafast lasers (namely the contour of constant intensity in space and time within the pulse) [3]. Here, we present the first practical application of this pulse front adaptive optics method.…”

“…(1) that the delay has a quadratic relationship with the radius r. We therefore chose to demonstrate adaptive correction of pulse front distortion by introducing a quadratic shaped pulse front to the laser light. Applying opposite quadratic phases to a deformable mirror (DM) and a spatial light modulator (SLM) that are imaged onto one another, we were able to maintain a flat phase front while generating a quadratic variation in the pulse front across the beam [3], as shown in the sketch of Fig. 1(b).…”

“…We use the equivalent optical path length (EOPL) to represent the peak-to-valley magnitude of the phase front applied to the dual adaptive optics elements (AOEs) and T PF to represent the peakto-valley time delay for the pulse front [T PF EOPL∕c, where c is the speed of light, shown in Fig. 1(c)] [3].…”