Justin Ratner

Coherent artifact in modern pulse measurements

All optical pulse cmeasurement techniques necessarily fail in multi-shot measurements of unstable pulse trains because the measurement can only provide a single result, despite of the presence of many different pulse shapes. At the very least, however, the technique should provide a reasonable estimate of a typical pulse in the train and indicate the trains stability. While frequency-resolved optical gating (FROG, [1]) and spectral phase interferometry for direct electric-field reconstruction (SPIDER, [2]) naturally operate single-shot, multi-shot variants are very common, so it is important to understand the effects of instability on multi-shot measurements.

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.

Characterization and testing of novel polarized nanomaterial textiles for ultrasensitive wireless gas sensors

A novel polarized nano-material (PNM) textile is fabricated and characterized at Ka-band (26.5 to 40 GHz) by rectangular waveguide measurements for three different polarization schemes (crossed, horizontal, and vertical polarized samples). Since carbon nanotubes were found to be ultra sensitive to different gases at extremely low concentration, a very important application is integrated gas sensors that are based on the change in the electrical properties of carbon nanotube materials induced by gas molecule adsorption. However, a systematic design methodology for high frequency gas sensors utilizing carbon nanotube materials is not yet possible due to the lack of in-depth knowledge on the material properties before and after being exposed to the gases of interests. In this study, the scattering parameters of PNM textile embedded in waveguides are measured in both room atmosphere and in ammonia/air mixture of 5% ammonia. The gas measurement show a phase shift of 10 degrees in S11 values. The impedance of the PNMs are computed from the scattering parameters in waveguide measurements, which for the first time experimentally show that CNTs can function as resonators at microwave frequencies.

Development of a fully-integrated ultrasensitive wireless sensor utilizing carbon nanotubes and surface plasmon theory

A practical application of surface plasmon resonance (SPR) for the realization of an ultrasensitive, fully-integrated, fully-packaged wireless sensor, that can operate in microwave frequencies based on the gas sensitivity of carbon nanotube (CNT) mixtures, is proposed. The sensor consists of a corrugated aluminum plate whose surface is periodically covered with a thin layer of the CNT materials. The incident TM-polarized waves on this surface excite the surface plasmon (SP) mode, thus resulting in a drop of power of the reflected wave. The change in the electrical properties of the CNT mixtures when exposed to gases results in the change of the SPR observable in the reflected waves. For the first time, a CNT-based wireless sensor has been designed to show a frequency shift of 400 MHz while operating in the 60 GHz range.

Simultaneous measurement of two different-color ultrashort pulses on a single shot

We experimentally demonstrate the ability of double blind frequency-resolved optical gating to simultaneously measure two independent pulses at very different wavelengths on a single shot. Our device uses polarization-gate geometry, allowing pulses at any two wavelengths and unlimited operating bandwidth. The retrieval algorithm is robust and is capable of ignoring most forms of noise in the measured spectrograms.

The coherent artifact in modern pulse measurements

All optical pulse cmeasurement techniques necessarily fail in multi-shot measurements of unstable pulse trains because the measurement can only provide a single result, despite of the presence of many different pulse shapes. At the very least, however, the technique should provide a reasonable estimate of a typical pulse in the train and indicate the trains stability. While frequency-resolved optical gating (FROG, [1]) and spectral phase interferometry for direct electric-field reconstruction (SPIDER, [2]) naturally operate single-shot, multi-shot variants are very common, so it is important to understand the effects of instability on multi-shot measurements.

The coherent artifact in modern pulse-shape measurements

We simulate multi-shot measurements of trains of pulses with unstable shapes using SPIDER, SRSI, SHG FROG, PG FROG, and XFROG. Interferometric methods measure only the coherent artifact, while FROG methods better approximate the trains.

The Coherent Artifact in Modern Pulse Measurements

We simulate multi-shot FROG and SPIDER measurements of unstable pulse trains, finding that FROG yields the approximate average duration, with disagreement between measured and retrieved traces, while SPIDER significantly under-estimates it, yielding only the coherent artifact.

Measuring Two Different-Color Ultrashort Pulses by Double Blind Polarization Gate Frequency-Resolved Optical Gating

Two independent ultrashort pulses at very different center wavelengths (400nm and 800nm) are measured simultaneously on a single shot using Double Blind Polarization Gate Frequency-Resolved Optical Gating.

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.