Pablo Gabolde

Crossed-beam spectral interferometry: a simple, high-spectral-resolution method for completely characterizing complex ultrashort pulses in real time

We present a high-spectral-resolution and experimentally simple version of spectral interferometry using optical fibers and crossed beams, which we call SEA TADPOLE. Rather than using collinear unknown and reference pulses separated in time to yield spectral fringes-and reduced spectral resolution-as in current versions, we use time-coincident pulses crossed at a small angle to generate spatial fringes. This allows the extraction of the spectral phase with the full spectrometer resolution, which allows the measurement of much longer and more complex pulses. In fact, SEA TADPOLE achieves spectral super-resolution, yielding the pulse spectrum with even better resolution. Avoiding collinear beams and using fiber coupling also vastly simplify alignment. We demonstrate SEA TADPOLE by measuring a chirped pulse, a double pulse separated by 14 ps, and a complex pulse comprising two trains of pulses with a time-bandwidth product of ~400.

Directly measuring the spatio-temporal electric field of focusing ultrashort pulses

We present the first technique for directly measuring (without assumptions) the spatio-temporal intensity and phase of a train of ultrashort pulses at and near a focus. Our method uses an experimentally simple and high-spectral resolution variant of spectral interferometry (SEA TADPOLE). To illustrate our technique, we measured the spatio-temporal electric field in and around the foci of several different types of lenses. To confirm our results, we also simulated these measurements by numerically propagating a pulse through each of the lenses used. From one set of measurements, we made a movie showing a focusing pulse with severe chromatic aberration.

Single-shot measurement of the full spatio-temporal field of ultrashort pulses with multi-spectral digital holography

We present a remarkably simple technique for measuring the full spatio-temporal electric field of a single ultrashort laser pulse. It involves capturing a large digital hologram containing multiple smaller holograms, each of which characterizes the spatial intensity and phase distributions of an individual frequency component of the pulse. From that single camera frame, we numerically reconstruct the complete electric field, E(x,y,t), using a direct algorithm. While holography requires a well-characterized reference pulse, this pulse can easily be generated from the pulse itself in most cases, so the technique is self-referencing. We experimentally demonstrate this technique using femtosecond pulses from a mode-locked Ti:Sapphire oscillator.

Simultaneous visualization of spatial and chromatic aberrations by two-dimensional Fourier transform spectral interferometry.

We demonstrate the use of a simple tool to simultaneously visualize and characterize chromatic and spherical aberrations that are present in multiphoton microscopy. Using two-dimensional Fourier transform spectral interferometry, we measured these aberrations, deducing in a single shot spatiotemporal effects in high-numerical-aperture objectives.

Measuring the spatiotemporal electric field of ultrashort pulses with high spatial and spectral resolution

We demonstrate an experimentally simple and high-spectral-resolution version of spectral interferometry (SEA TADPOLE) that can measure complicated pulses (in time) at video rates. Additionally, SEA TADPOLE can measure spatial information about a pulse, and it is the first technique that can directly measure the spatiotemporal electric field [E(x,y,z,λ)] of a focusing ultrashort pulse. To illustrate and test SEA TADPOLE, we measured E(λ) of a shaped pulse that had a time-bandwidth product of approximately 100. To demonstrate that SEA TADPOLE can measure focusing pulses, we measured E(x,λ) at and around the focus produced by a plano-convex lens. We also measured the focus of a beam that had angular dispersion present before the lens. We have found that SEA TADPOLE can achieve better spectral resolution than an equivalent spectrometer, and here we discuss this in detail, giving both experimental and simulated examples. We also discuss the angular acceptance and spatial resolution of SEA TADPOLE when measuring the spatiotemporal field of a focusing pulse.

Self-referenced measurement of the complete electric field of ultrashort pulses

A self-referenced technique based on digital holography and frequency-resolved optical gating is proposed in order to characterize the complete complex electric field E(x,y,z,t) of a train of ultrashort laser pulses. We apply this technique to pulses generated by a mode-locked Ti:Sapphire oscillator and demonstrate that our device reveals and measures common linear spatio-temporal couplings such as spatial chirp and pulse-front tilt.

Single-frame measurement of the complete spatiotemporal intensity and phase of ultrashort laser pulses using wavelength-multiplexed digital holography

We show that a simple (few-element) arrangement for wavelength-multiplexed digital holography allows the measurement of the electric field E(x,y,t) of a femtosecond laser pulse on a single shot. A slightly rotated two-dimensional diffractive optical element and a variable-wavelength filter together generate multiple spectrally resolved digital holograms that are simultaneously captured in a single frame by a digital camera. An additional simultaneous measurement of the spectral phase for a spatially filtered replica of the pulse with frequency-resolved optical gating completes this three-dimensional measurement. An experimental implementation of the technique is presented and its current limitations are discussed.

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.