Ilya Dunayevskiy

Ring resonator-based electrooptic polymer traveling-wave modulator

The authors report the bandpass-modulation characteristics of a ring resonator-based traveling-wave modulator using an electrooptic polymer AJL8/APC. The use of the traveling-wave electrode makes it possible to achieve an efficient modulation around 28 GHz, which is the free spectral range of the resonator, with a 3-dB bandwidth of 7 GHz. The modulation sensitivity is evaluated by defining an equivalent half-wave voltage of ring modulators. It is shown that the modulator has a potential in the microwave and millimeter-wave photonics applications

High-sensitivity detection of triacetone triperoxide (TATP) and its precursor acetone

Triacetone triperoxide (C(9)H(18)O(6), molecular mass of 222.24 g/mol) (TATP) is a powerful explosive that is easy to synthesize using commonly available household chemicals, acetone, and hydrogen peroxide 1 2. Because of the simplicity of its synthesis, TATP is often the explosive of choice for terrorists, including suicide bombers. For providing safety to the population, early detection of TATP and isolation of such individuals are essential. We report unambiguous, high-sensitivity detection of TATP and its precursor, acetone, using room-temperature quantum cascade laser photoacoustic spectroscopy (QCL-PAS). The available sensitivity is such that TATP, carried on a person (at a nominal body temperature of 37 degrees C), should be detectable at some distance. The combination of demonstrated detection of TATP and acetone should be ideal for screening at airports and other public places for providing increased public safety.

Optically multiplexed multi-gas detection using quantum cascade laser photoacoustic spectroscopy.

We report high-throughput, nondispersive optical multiplexing of laser beams using a scanning galvanometer. We have utilized this technique for multispecies trace-gas detection using multiple quantum cascade laser photoacoustic spectroscopy. We demonstrate switching from one laser to another in less than 1 s, a performance level needed for a comprehensive multispecies sensor, and a high signal-to-noise ratio detection of five gaseous components, NH(3), NO(2), dimethyl methyl phosphonate (DMMP, a simulant for nerve agents), acetone, and ethylene glycol, in a room air gas mixture containing approximately 3 ppb of NH(3), approximately 8 ppb of NO(2), approximately 20 ppb of DMMP, approximately 30 ppb of acetone, and approximately 40 ppb of ethylene glycol.

External cavity quantum cascade lasers with ultra rapid acousto-optic tuning

We report operation of tunable external cavity quantum cascade lasers with emission wavelength controlled by an acousto-optic modulator (AOM). A long-wave infrared quantum cascade laser wavelength tuned from ∼8.5 μm to ∼9.8 μm when the AOM frequency was changed from ∼41MHz to ∼49 MHz. The laser delivered over 350 mW of average power at the center of the tuning curve in a linewidth of ∼4.7 cm−1. Measured wavelength switching time between any two wavelengths within the tuning range of the QCL was less than 1 μs. Spectral measurements of infrared absorption features of Freon demonstrated a capability of obtaining complete spectral data in less than 20 μs.

Sub-parts-per-billion level detection of dimethyl methyl phosphonate (DMMP) by quantum cascade laser photoacoustic spectroscopy.

The need for the detection of chemical warfare agents (CWAs) is no longer confined to battlefield environments because of at least one confirmed terrorist attack, the Tokyo Subway [Emerg. Infect. Dis. 5, 513 (1999)] in 1995, and a suspected, i.e., a false-alarm of a CWA in the Russell Senate Office Building [Washington Post, 9 February 2006, p. B01]. Therefore, detection of CWAs with high sensitivity and low false-alarm rates is considered an important priority for ensuring public safety. We report a minimum detection level for a CWA simulant, dimethyl methyl phosphonate (DMMP), of <0.5 ppb (parts in 10(9)) by use of a widely tunable external grating cavity quantum cascade laser and photoacoustic spectroscopy. With interferents present in Santa Monica, California street air, we demonstrate a false-alarm rate of 1:10(6) at a detection threshold of 1.6 ppb.

Millimeter- and submillimeter-wave characterization of various fabrics

Transmission measurements of 14 fabrics are presented in the millimeter-wave and submillimeter-wave electromagnetic regions from 130 GHz to 1.2 THz. Three independent sources and experimental set-ups were used to obtain accurate results over a wide spectral range. Reflectivity, a useful parameter for imaging applications, was also measured for a subset of samples in the submillimeter-wave regime along with polarization sensitivity of the transmitted beam and transmission through doubled layers. All of the measurements were performed in free space. Details of these experimental set-ups along with their respective challenges are presented.

Continuous wave operation of quantum cascade lasers with frequency-shifted feedback

Operation of continuous wave quantum cascade lasers with a frequency-shifted feedback provided by an acousto-optic modulator is reported. Measured linewidth of 1.7 cm−1 for these devices, under CW operating conditions, was in a good agreement with predictions of a model based on frequency-shifted feedback seeded by spontaneous emission. Linewidth broadening was observed for short sweep times, consistent with sound wave grating period variation across the illuminated area on the acousto-optic modulator. Standoff detection capability of the AOM-based QCL setup was demonstrated for several solid materials.

Fast evanescent wave spectroscopy in the long wave infrared

We report evanescent wave long wave infrared (LWIR) spectroscopy on a microsecond wavelength switching time scale using the recently developed acousto-optic modulator (AOM) tuned quantum cascade laser. We have examined several liquids to demonstrate the technique and they include isopropyl alcohol (IPA), ethanol, water, alcoholic beverage such as vodka, gin and whiskey, 2,2,2-trifluroethanol and Epsom salt dissolved in water. We also carried out dilution studies of absolute ethanol with water. We find that the commercially available vodka, gin and scotch alcohol concentrations fit well with our calibration. In each of these cases, we were able to collect spectral data from ~8.6 μm to ~9.5 μm in a spectral scan time of <500 μs. The fast data collection capability point to applications of the AOM tuned QCL system as a real time process control tool where flowing fluids are mixed for production of new chemical and biological end products.

Two wavelength operation of an acousto-optically tuned quantum cascade laser and direct measurements of quantum cascade laser level lifetimes

We report simultaneous two wavelength operation of an acousto-optically tuned quantum cascade laser (QCL). The two wavelengths can be independently tuned as well as independently switched, retaining the submicrosecond switching capability. In addition, we have used the two wavelength operation as a tool for the direct measure of the lifetimes of the lasing states in a practical QCL. The lifetime measurements in an operational QCL are facilitated by our ability to vary the frequency separation between two simultaneously lasing wavelengths. The measured lifetime is 0.6 ps ± 0.2 ps for our quantum cascade laser. The two wavelength operation of QCLs paves the way for time resolved pump/probe studies of infrared phenomena and provides direct insight into the effectiveness of various QCL structure designs.

Demonstration of 28 GHz ring resonator based electro-optic polymer modulator

We demonstrate a ring resonator based traveling wave electro-optic polymer modulator. Efficient modulation at 28 GHz (FSR of the resonator) with 3 dBe bandwidth of 7 GHz is achieved.