Toward Programmable Ultrashort Pulse Characterization

Abstract

Although numerous self-referenced techniques have been proposed and demonstrated to measure or characterize the time-dependent phase and amplitude of ultrashort pulses, all techniques suffer from specific weaknesses. To overcome the drawbacks, limitations or ambiguities related to a particular technique, crosscheck between several techniques is often required to improve the measurement or eliminate spurious results. However, crosschecking between techniques as different as SH-FROG[2] and SPIDER[1] is often made difficult by the fact that they involve separate measurement devices, which multiplies the causes of systematic experimental errors: calibration of the detectors, dispersion of the optical elements...In this talk, we present a programmable pulse measurement device based on an acousto-optic programmable dispersive filter (AOPDF) [3]. This device is single-beam and able to implement either SPIDER, SH-FROG or interferometric SH-FROG pulse characterization techniques with the same optical layout. Experimental demonstrations of SPIDER and SH-FROG techniques are provided on an amplified kHz laser system delivering 10nm bandwidth pulses at -800nm.This device contains an AOPDF (high resolution cut, 25mm long crystal), a retardation plate, a type II BBO second harmonic generation stage and a spectrometer (Fig. 1). In SH-FROG mode, the AOPDF is set to produce a pair of replicas of the input short pulse E(t) of duration TO. The acoustic waveforms corresponding to each set of replicas are computed, stored in separate memories of the AOPDF driver and then recalled one after the other at the repetition rate or at a fraction of the repetition rate of the laser. Since the two pulses are diffracted on the same beam, both are linearly polarized and the polarization of one of the two replicas must be rotated or projected in order to get type II sum frequency generation of the two replicas. To do so, the diffracted beam is sent through a 6mm thick retardation plate made of Calcite. This birefringent FROG SPIDER 3 6ps calcite delay 3 6ps calcite delay Calcite plate SHG /\ X1 A0I o AOPDF Spectromete e Lens Lens SHG 11 SHG 11 Fig. 1. a) experimental setup. b) and c) time diagram at the output of the calcite plate showing the pulse sequences used for SH-FROG and SPIDER.plate is cut such that its optical axis is perpendicular to the direction of incidence and orientated at 45 degrees from the polarization plane of the diffracted beam. With this setup, the fraction of pulse replicas which is extraordinary polarized is delayed with respect to the ordinary polarized part by a group delay of Tc 3.6ps. As depicted in figure 1, when the delay between the two replicas is set to be Tr = Tc + T with T < Tc-To, the spectrally resolved II SHG signal measured is exactly equal to the SH-FROG signal. In SPIDER mode, the AOPDF is set to produce three pulses: two replicas of the input pulse with a 1.5ps interpulse delay and one narrowband highly chirped pulse. The same Calcite plate is used to overlap the pulse replicas with the chirped pulse (fi...

A newcomer's guide to ultrashort pulse shaping and characterization

“…Depending on the sequence of waveforms used, many different techniques can be implemented. Indeed, variants of both FROG [179,180,178] and SPIDER [160,181,180] have been implemented using this approach.…”

“…Recording the spectra as a function of the delay gives an interferometric FROG (iFROG) trace. The classical FROG trace can be extracted by Fourier processing [178] (see Fig.33(c)) or obtained directly using calcite plate and type II crystal to avoid interferences [180]. Figure 33(a) taken in ref.…”

“…One major advantage of all the shaper assisted characterization techniques is that the exact same set-up can be used to achieve several quasi-independent measurements of the same pulse, by simply changing the sequence of the waveforms used in order to implement different characterization techniques [179,180,178]. This constitute a unique advantage of shaper assisted characterization techniques over traditional ones where each technique relies on a dedicated experimental set-up.…”