Thomas H. Chyba

Tetragonal vanadates YVO4 and GdVO4 – new efficient χ(3)-materials for Raman lasers

Abstract Efficient room temperature multiple Stokes and anti-Stokes picosecond generation in tetragonal YVO4 and GdVO4 host crystals for lasing trivalent lanthanides (Ln3+) has been observed for the first time. All measured stimulated Raman scattering (SRS) wavelengths in the visible and near infrared are identified and attributed to the SRS-active vibration modes of these vanadates.

High efficiency nanosecond Raman lasers based on tetragonal PbWO4 crystals

Abstract We report on laser action in linear and ring Raman oscillators based on novel χ (3) -active PbWO 4 crystals with scheelite structure ( ω R =901 cm −1 ). These resonators are pumped by the fundamental and the second harmonic wavelengths, respectively, of a Q-switched Nd 3+ :Y 3 Al 5 O 12 laser. In these preliminary measurements, conversion efficiencies as high as 20% are observed. To our knowledge, this is the first such demonstration of Raman lasing in lead tungstate in the nanosecond regime. Raman lasers based on PbWO 4 are very promising for several applications, including the generation of wavelengths in the uv (in conjunction with other nonlinear processes) for ozone differential absorption lidar. This material has optical transparency from ≈0.33 to ≈5.5 μm, making it also potentially useful for trace gas detection in the infrared. Furthermore, it has a high damage threshold and is not hydroscopic. Some new data on picosecond high-order Stokes and anti-Stokes generation are also presented. In particular, our SRS experiments with a 1-μm Nd 3+ :Y 3 Al 5 O 12 pump laser demonstrate multiple anti-Stokes emission up to the 10th component with λ ASt10 =0.5433 μm.

Solid-state barium nitrate Raman laser in the visible region

Abstract Preliminary results on a compact, visible barium nitrate Raman laser have been obtained. A total conversion efficiency greater than 65% at PRF of 30 Hz may make this a suitable laser for ozone DIAL when doubled to the UV region.

Spectral unmixing of agents on surfaces for the Joint Contaminated Surface Detector (JCSD)

ITT Corporation, Advanced Engineering and Sciences Division, is currently developing the Joint Contaminated Surface Detector (JCSD) technology under an Advanced Concept Technology Demonstration (ACTD) managed jointly by the U.S. Army Research, Development, and Engineering Command (RDECOM) and the Joint Project Manager for Nuclear, Biological, and Chemical Contamination Avoidance for incorporation on the Armys future reconnaissance vehicles. This paper describes the design of the chemical agent identification (ID) algorithm associated with JCSD. The algorithm detects target chemicals mixed with surface and interferent signatures. Simulated data sets were generated from real instrument measurements to support a matrix of parameters based on a Design Of Experiments approach (DOE). Decisions based on receiver operating characteristics (ROC) curves and area-under-the-curve (AUC) measures were used to down-select between several ID algorithms. Results from top performing algorithms were then combined via a fusion approach to converge towards optimum rates of detections and false alarms. This paper describes the process associated with the algorithm design and provides an illustrating example.

Design validation of an eye-safe scanning aerosol lidar with the Center for Lidar and Atmospheric Sciences Students (CLASS) at Hampton University

ITTs Advanced Engineering and Sciences Division and the Hampton University Center for Lidar and Atmospheric Sciences Students (CLASS) team have worked closely to design, fabricate and test an eye-safe, scanning aerosol-lidar system that can be safely deployed and used by students form a variety of disciplines. CLASS is a 5-year undergraduate- research training program funded by NASA to provide hands-on atmospheric-science and lidar-technology education. The system is based on a 1.5 micron, 125 mJ, 20 Hz eye-safe optical parametric oscillator (OPO) and will be used by the HU researchers and students to evaluate the biological impact of aerosols, clouds, and pollution a variety of systems issues. The system design tasks we addressed include the development of software to calculate eye-safety levels and to model lidar performance, implementation of eye-safety features in the lidar transmitter, optimization of the receiver using optical ray tracing software, evaluation of detectors and amplifiers in the near RI, test of OPO and receiver technology, development of hardware and software for laser and scanner control and video display of the scan region.

A algorithm benchmark data suite for chemical and biological (chem/bio) defense applications

A Chem/Bio Defense Algorithm Benchmark is proposed as a way to leverage algorithm expertise and apply it to high fidelity Chem/Bio challenge problems in a high fidelity simulation environment. Initially intended to provide risk mitigation to the DTRA-sponsored US Army CUGR ACTD, its intent is to enable the assessment and transition of algorithms to support P3I of future spiral updates. The key chemical sensor in the CUGR ACTD is the Joint Contaminated Surface Detector (JCSD), a short-range stand-off Raman spectroscopy sensor for tactical in-the-field applications. The significant challenges in discriminating chemical signatures in such a system include, but are not limited to, complex background clutter and low signal to noise ratios (SNR). This paper will present an overview of the Chem-Bio Defense Algorithm Benchmark, and the JCSD Challenge Problem specifically.

Laser interrogation of surface agents (LISA) for chemical agent reconnaissance

Laser Interrogation of Surface Agents (LISA) is a new technique which exploits Raman scattering to provide standoff detection and identification of surface-deposited chemical agents. ITT Industries, Advanced Engineering and Sciences Division is developing the LISA technology under a cost-sharing arrangement with the US Army Soldier and Biological Chemical Command for incorporation on the Armys future reconnaissance vehicles. A field-engineered prototype LISA-Recon system is being designed to demonstrate on-the- move measurements of chemical contaminants. In this article, we will describe the LISA technique, data form proof-of- concept measurements, the LISA-Recon design, and some of the future realizations envisioned for military sensing applications.

High resolution spectral measurements of Raman shifts in barium nitrate

High resolution spectral measurements of the first, second, and third Stokes shifts in barium nitrate are reported. The laser source for the experiment is a frequency-doubled, injection-seeded Nd:YAG laser. Spectra for both single-pass conversion and for a Raman oscillator are compared. Significant gain narrowing of the spectrum is observed.

Long-range standoff detection of chemical, biological, and explosive hazards on surfaces

Fielded surface detection systems rely on contact with either the liquid contamination itself or the associated chemical vapor above the contaminated surface and do not provide a standoff or remote detection capability. Conversely, standoff chemical vapor sensing techniques have not shown efficacy in detecting those contaminants as liquids or solids on surfaces. There are a number of optical or spectroscopic techniques that could be applied to this problem of standoff chemical detection on surfaces. The three techniques that have received the most interest and development are laser induced breakdown spectroscopy (LIBS), fluorescence, and Raman spectroscopy. Details will be presented on the development of these techniques and their applicability to detecting CBRNE contamination on surfaces.

Cleanliness and damage measurements of optics in atmospheric sensing high energy lasers

Langley Research Center has several atmospheric remote sensing programs which utilize high energy pulsed lasers. These lasers typically have many damaged optics after several million shots. Damage is defined herein as color changes and/or optical flaws seen in microscopic inspection, and does not necessarily relate to measured performance degradation of the optic. Inspections and measurements of some of these optics indicate that energy thresholds for several million shots damage is about an order of magnitude lower than that for single shot damage. Damage initiation is often at micron size areas at the coating interface, which grows and sometimes develops as erosion of the top of the coating. There is a wide range in polish and coating quality of new optics, even on different faces of the same optic. Military Standard 1246C can be used to provide overall particulate, and molecular film, or nonvolatile residue cleanliness scales. Microscopic inspections and photography at 10X to 500X with brightfield (perpendicular) and darkfield (oblique) illumination are useful in assigning cleanliness levels of new and in-service optics. Microextraction (effecting concentration of molecular films to small areas) provides for enhanced optical detection and surface film chemical analysis by electron-microscope energy-dispersive-spectroscopy. Similar measurement techniques can be used to characterize and document optical damage initiation and optical damage growth. Surface contamination interferes with and complicated measurements of polish and coating quality, and of optical damage. Our work indicates ultrasonic cleaning, and packaging of optics in Teflon sleeves or cups is advantageous over conventional cleaning and packaging for characterization of new optics.