Vikrant Chauhan

Single-diffraction-grating and grism pulse compressors

We introduce and demonstrate a simple, compact, and automatically aligned ultrashort-pulse compressor that uses only a single diffraction element—a grating or a grism (a grating on a prism). This design automatically has unity beam magnification and automatically contributes zero spatiotemporal distortions to the pulse, thus avoiding spatial chirp, angular dispersion, pulse-front tilt, and all other first-order spatiotemporal distortions. It is comprised of only three elements: a diffraction element, a corner cube, and a roof mirror. Half the size of comparable two-grating compressors, it can provide large amounts of negative group-delay dispersion with small translations of the corner cube. The device can operate on pulses with both large and small bandwidths by varying the corner-cube position. Using a grism as the diffraction element, material dispersion up to the third order can be compensated, and we demonstrated compensation for 10 m of optical fiber for 800 nm pulses.

Measuring temporally complex ultrashort pulses using multiple-delay crossed-beam spectral interferometry.

We introduce a spectral-interferometry (SI) technique for measuring the complete intensity and phase of relatively long and very complex ultrashort pulses. Ordinarily, such a method would require a high-resolution spectrometer, but our method overcomes this need. It involves making multiple measurements using SI (in its SEA TADPOLE variation) at numerous delays, measuring many temporal pulselets within the pulse, and concatenating the resulting pulselets. Its spectral resolution is the inverse delay range--many times higher than that of the spectrometer used. Our simple proof-of-principle implementation of it provided 71 fs temporal resolution and a temporal range of 100 ps using a few-cm low-resolution spectrometer.

Simultaneously measuring two ultrashort laser pulses on a single-shot using double-blind frequency-resolved optical gating

We demonstrate a simple self-referenced single-shot method for simultaneously measuring two different arbitrary pulses, which can potentially be complex and also have very different wavelengths. The method is a variation of cross-correlation frequency-resolved optical gating (XFROG) that we call double-blind (DB) FROG. It involves measuring two spectrograms, both of which are obtained simultaneously in a single apparatus. DB FROG retrieves both pulses robustly by using the standard XFROG algorithm, implemented alternately on each of the traces, taking one pulse to be “known” and solving for the other. We show both numerically and experimentally that DB FROG using a polarization-gating beam geometry works reliably and appears to have no nontrivial ambiguities.

Distortion-Free Single-Prism/Grating Ultrashort Laser Pulse Compressor

We introduce an ultrashort laser pulse compressor that uses a single-prism and a single-grating. It is compact and automatically aligned and compensates for significant second- and third-order material dispersion. This design inherently has unity beam magnification and automatically contributes zero spatiotemporal distortions to the pulse, thus avoiding spatial chirp, angular dispersion, pulse-front tilt, and all other first-order spatiotemporal distortions common to pulse compressors. It is comprised of only four elements: a prism, a diffraction grating, a corner cube, and a roof mirror. It can provide large amounts of negative group-delay dispersion with small translations of the corner cube. Unlike conventional compressors, the device can operate on pulses with both large and small bandwidths by varying the corner cube position. Using this compressor, we demonstrate compensation of 12 m of optical fiber for 800-nm pulses with 30 nm of bandwidth.

Measuring extremely complex pulses with time-bandwidth products exceeding 65,000 using multiple-delay crossed-beam spectral interferometry.

We measure the complete electric field of extremely complex ultrafast waveforms using the simple linear-optical, interferometric pulse-measurement technique, MUD TADPOLE. The waveforms were measured with ~40 fs temporal resolution over a temporal range of ~3.5 ns and had time-bandwidth products exceeding 65,000. The approach is general and could allow the measurement of arbitrary optical waveforms.

Propagation dependence of chirp in Gaussian pulses and beams due to angular dispersion

The chirp acquired by a Gaussian ultrashort pulse due to angular dispersion, unlike that of plane waves, increases nonlinearly with propagation distance and eventually asymptotes to a constant. However, this interesting result has never been directly measured. In this Letter, we use two-dimensional spectral interferometry to measure the propagation dependence of the chirp for Gaussian ultrashort pulses and beams with angular dispersion. The measured chirp as a function of propagation distance agreed well with theory. This work verifies both an equation and a measurement technique that will be useful for predicting or determining the pulses chirp in ultrafast optics experiments that contain angular dispersion.

Single-grating and single-grism pulse compressors

We introduce single-grating and single-grism pulse compressors, which are compact and automatically aligned for distortion-free output, and the latter of which compensates for significant material dispersion up to third order.

Using Blind Deconvolution to Simultaneously Retrieve Two Ultrashort Laser Pulses

We demonstrate a simple method, based on blind deconvolution, for simultaneously measuring two arbitrary ultrashort laser pulses.

Measuring complex pulses with time-bandwidth products exceeding 65,000 using multiple-delay crossed-beam spectral interferometry

We measure the complete electric field of extremely complex ultrafast waveforms using the simple linear-optical, interferometric pulse-measurement technique, MUD TADPOLE. In its scanning variation, we measured waveforms with time-bandwidth products exceeding 65,000 with ~40 fs temporal resolution over a temporal range of ~3.5ns. In the single-shot variation we measured complex waveforms time-bandwidth products exceeding 65,000. The approach is general and could allow the measurement of arbitrary optical waveforms.

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.