An analysis of the single point reproducibility of TD-THz based paint thickness measurements demonstrated a precision
of 130 nm, corresponding to 0.1% of the measured thickness. A detailed model of the anticipated TD-THz waveforms
from samples of varying thickness indicates that an intrinsic uncertainty of 0.09% is anticipated in the absence of
environmental fluctuations. Therefore, the influence of oscillations in the THz field associated with the initial reflection
does not adversely impact the ability to extract accurate paint thickness information, and the noise associated with these
oscillations could limit the measurement uncertainty of a calibrated instrument under optimum laboratory conditions. In
the case of a deployed sensor, we anticipate that the accuracy will be degraded by environmental fluctuations.
We report on the first successful installation of a commercial solid-state sodium guidestar laser system (GLS). The GLS developed at LMCT was delivered to Gemini North Observatory in February of 2005. The laser is a single beacon system that implements a novel laser architecture and represents a critical step towards addressing the need of the astronomy and military adaptive optics (AO) communities for a robust turn-key commercial GLS. The laser was installed on the center section of the 8 m Gemini North telescope, with the output beam relayed to a laser launch telescope located behind the 1 m diameter secondary mirror. The laser went through a three week performance evaluation between November and December 2005 wherein it consistently generated 12 W average power with measured M2 < 1.1 while locked to the D2 line at +/- 100 MHz. The system was required to perform during a 12-hour test period during three runs of 4-6 consecutive nights each. The laser architecture is based on continuous wave (CW) mode-locked solid-state lasers. The mode-locked format enables more efficient SFG conversion, and dispenses with complex resonant intensity enhancement systems and injection-locking electronics. The linearly-polarized, near-diffraction-limited, modelocked 1319 nm and 1064 nm pulses are generated in separate dual-head diode-pumped resonators. The two IR pulses are input into a single-stage, 30 mm PPSLT sum-frequency generation (SFG) crystal provided by Physical Science, Inc. Visible (589 nm) power of >16 W have been generated, representing a conversion efficiency of 40%.
We have demonstrated 3.5W of 589nm light from a fiber laser using periodically poled stoichio-metric Lithium Tantalate (PPSLT) as the frequency conversion crystal. The system employs 938nm and 1583nm fiber lasers, which were sum-frequency mixed in PPSLT to generate 589nm light. The 938nm fiber laser consists of a single frequency diode laser master oscillator (200mW), which was amplified in two
stages to >15W using cladding pumped Nd3+ fiber amplifiers. The fiber amplifiers operate at 938nm and minimize amplified spontaneous emission at 1088nm by employing a specialty fiber design, which maximizes the core size relative to the cladding diameter. This design allows the 3-level laser system to operate at high inversion, thus making it competitive with the 1088nm 4-level laser transition. At 15W, the 938nm laser has an M2 of 1.1 and good polarization (correctable with a quarter and half wave plate to >15:1). The 1583nm fiber laser consists of a Koheras 1583nm fiber DFB laser that is pre-amplified to 100mW, phase modulated and then amplified to 14W in a commercial IPG fiber amplifier. As a part of our research efforts we are also investigating pulsed laser formats and power scaling of the 589nm system. We will discuss the fiber laser design and operation as well as our results in power scaling at 589nm.
Recent advances in current-pumped, bandgap-engineered semiconductor lasers have dramatically impacted laser-based sensor concepts for in-situ trace species measurement and standoff sensing applications. These devices allow a common technology platform to access strong fundamental vibrational absorption transitions of many gases, liquids, and solids in the mid-wave and long-wave IR, as well as far-IR, or THz. The THz wavelength region is particularly interesting for applications related to structure penetrating detection of hidden materials and biomolecular spectroscopy. This presentation will briefly review the important properties of these lasers as they apply to sensor design and present highlights of recent sensor development activity for trace gas analysis in environmental and biomedical applications, remote sensing LIDAR systems, and detection of hidden explosives.
Periodically poled, nearly-stoichiometric lithium tantalate has used to generate visible radiation (by second-harmonic generation using Nd:YAG laser) and mid-infrared radiation (by difference-frequency generation using a Nd:YAG laser and a tunable telecommunications-band laser). Phase-matching conditions have been measured for both interactions at temperatures between 25 degrees Centigrade and 131 degrees centigrade. The absolute conversion efficiency for SHG has been measured and used to derive an effective nonlinear optical coefficient for this process in the periodically poled material. These results can be used to guide the design of laser systems based on nonlinear optical frequency conversion in periodically poled nearly-stoichiometric lithium tantalate.
The periodic poling of stoichiometric lithium tantalate, a nonlinear optical material with great promise for the frequency conversion of high-average-power solid state lasers, has been investigated. Two problems with commercially available stoichiometric lithium tantalate substrates have been identified: non-reproducibility of the coercive field from one wafer to the next, and susceptibility to the formation of micro-domain defects. Strategies for dealing with these problems have been developed. Wafer-scale poling has been carried out to produce quasi-phasematching gratings with periods as short as 7.3 microns on half-millimeter thick substrates and 25.4 microns on millimeter-thick substrates. The phase-matching properties of periodically poled stoichiometric lithium tantalate have been measured using nonlinear optical frequency conversion. For processes which generate visible radiation, good agreement with predictions based on the published Sellmeier equation for stoichiometric lithium tantalite has been obtained.
The THz spectra of the high explosives, HMX, RDX, PETN, and TNT were measured using the technique of Time Domain THz (TD-THz) spectroscopy, and resonances attributed to phonon bands were observed. The TD-THz methods used to obtain these spectra are described and strategies for improved data collection methods are outlined. Concepts for through container DIfferential Absorption Lidar (DIAL) are outlined and the suitability of TD-THz methods for DIAL sensing is discussed.
The potential container penetrating capabilities of THz radiation leads to possible applications for container penetrating sensors for biological hazards. Such an approach requires the presence of distinct THz frequency resonances in the target compounds coupled with sufficiently transparent container materials to allow through container sensing. The results of a THz spectroscopic survey of container and clothing materials are presented along with spectra of materials that were chosen as simulants and markers for illicit biological substances.
The spectroscopic data presented show at least partial transparency for materials commonly used for clothing and packaging. We also measure distinct spectral signatures in dipicolinic acid, calcium dipicolinate, peptidoglycan, and 2,6-diaminopimelic acid, biologically significant molecules that are indicative of hazardous spore forming bacteria. These spectra differ significantly from those of the container materials to provide a potential contrast mechanism which could be used for identification.
We demonstrate a new tunable mid-IR laser source based on the guided-wave frequency conversion of two diode lasers operating in the near-infrared. Important features of this laser source include portability, room-temperature operation, freedom from thermal cycling, smooth tunability, and modular construction using readily available components. The source, when fully optimized, will maintain the properties which have made lead-salt lasers so useful for atmospheric trace gas detection, including sub-Doppler linewidths, microwatt-level output powers, and amenability to detection techniques based on frequency modulation. We describe the design and construction of the laser source, including its key component: a waveguide fabricated in periodically poled lithium niobate. In addition, we present a laboratory absorption spectrum which illustrates the potential usefulness of this laser source for the detection of atmospheric methane. Difficulties encountered when making the transition from a laboratory tabletop device to a portable device are discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.