The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

/pdf/optical-gas-sensing-a-review-4uaf589xiq.pdf

Optical gas sensing: a review

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted considerable interest due to their superior physicochemical features, such as large anti-Stokes shifts, low autofluorescence background, low toxicity and high penetration depth, which make them extremely suitable for use as alternatives to conventional downshifting luminescence bioprobes like organic dyes and quantum dots for various biological applications. A fundamental understanding of the photophysics of lanthanide-doped UCNPs is of vital importance for discovering novel optical properties and exploring their new applications. In this review, we focus on the most recent advances in the development of lanthanide-doped UCNPs as potential luminescent nano-bioprobes by means of our customized lanthanide photophysics measurement platforms specially designed for upconversion luminescence, which covers from their fundamental photophysics to bioapplications, including electronic structures (energy levels and local site symmetry of emitters), excited-state dynamics, optical property designing, and their promising applications for in vitro biodetection of tumor markers. Some future prospects and efforts towards this rapidly growing field are also envisioned.

Lanthanide-doped upconversion nano-bioprobes: electronic structures, optical properties, and biodetection

Nonlinear Optical Crystals: A Complete Survey

Within the field of spectral imaging, the vast majority of instruments used are scanning devices. Recently, several snapshot spectral imaging systems have become commercially available, providing new functionality for users and opening up the field to a wide array of new applications. A comprehensive survey of the available snapshot technologies is provided, and an attempt has been made to show how the new capabilities of snapshot approaches can be fully utilized.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-52/issue-9/090901/Review-of-snapshot-spectral-imaging-technologies/10.1117/1.OE.52.9.090901.pdf

Review of snapshot spectral imaging technologies

Autonomous navigation in cross-country environments presents many new challenges with respect to more traditional, urban environments. The lack of highly structured components in the scene complicates the design of even basic functionalities such as obstacle detection. In addition to the geometric description of the scene, terrain typing is also an important component of the perceptual system. Recognizing the different classes of terrain and obstacles enables the path planner to choose the most efficient route toward the desired goal.

This paper presents new sensor processing algorithms that are suitable for cross-country autonomous navigation. We consider two sensor systems that complement each other in an ideal sensor suite: a color stereo camera, and a single axis ladar. We propose an obstacle detection technique, based on stereo range measurements, that does not rely on typical structural assumption on the scene (such as the presence of a visible ground plane)s a color-based classification system to label the detected obstacles according to a set of terrain classess and an algorithm for the analysis of ladar data that allows one to discriminate between grass and obstacles (such as tree trunks or rocks), even when such obstacles are partially hidden in the grass. These algorithms have been developed and implemented by the Jet Propulsion Laboratory (JPL) as part of its involvement in a number of projects sponsored by the US Department of Defense, and have enabled safe autonomous navigation in high-vegetated, off-road terrain.

/pdf/obstacle-detection-and-terrain-classification-for-autonomous-56lyfce1fy.pdf

Obstacle Detection and Terrain Classification for Autonomous Off-Road Navigation

Quantum efficiency of the Nd 4F3/2 manifold is measured in 10 Nd-doped systems. Luminescence decay in these Nd-doped materials is nonexponential. Evidence for correlation between the nonexponential decay and reduced quantum efficiency is presented.

Quantum efficiency measurements in Nd-doped materials

This paper describes the first ever 2-μm diode-pumped Ho:Tm:YLF power oscillator generating wind quality, Q- switched output of 100 mJ at 6 Hz for coherent wind measurements from a space platform.

Diode-pumped all solid-state 2-µm power oscillator

Summary form only given. We study the possibility of broadening and compositional tuning of the 0.8 /spl mu/m absorption lines and the 0.94 and 1.06 /spl mu/m emission lines in Nd doped (Ba/sub x/Sr/sub 1-x/)/sub 5/(PO/sub 4/)/sub 3/F, (Ca/sub 1-x/Sr/sub x/)/sub 5/(PO/sub 4/)/sub 3/F, Sr/sub 5/(P/sub 1-x/V/sub x/O/sub 4/)/sub 3/F, and Ba/sub 5/(P/sub 1-x/V/sub x/O/sub 4/)/sub 3/F. These crystals have been grown by the Czochralski technique and have good optical quality. The emission wavelengths in the end members are in a fair agreement with our theoretical calculation of the Stark energy levels.

http://ieeexplore.ieee.org/iel5/6638/17705/00834579.pdf

Compositional wavelength tuning at the /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 11/2/ and /sup 4/F/sub 3/2//spl rarr//sup 4/F/sub 9/2/ transitions in Nd doped mixed apatite crystals

Developmental results for solid-state lasers for the mid-IR region are reviewed. Good slope efficiency and reasonable thresholds have been demonstrated for multiply doped mid-IR lasers. Laser efficiency increases as the operating temperature is decreased, due to both reduced threshold and a higher slope efficiency. Good slope efficiencies have been achieved even at room temperature. While Q-switching has been demonstrated at room temperature, it is not nearly as efficient as it is at reduced temperatures.

Solid-State Lasers For The Mid-Infrared Region

NASA is engaged in monitoring the health of planet Earth and exploring the other planets. For the former, global measurements of critical Earth parameters including ice sheet thickness, greenhouse gases, oxygen, wind velocity, and aerosols, are required. Highly specialized lasers, sometimes at new laser wavelengths, are needed to measure these variables. There are three approaches for this laser development being pursued by NASA. First, rather than seeking new lasers employing an empirical approach, a quantum mechanical model is used to predict better new lasers. Second, where lasers exist but the wavelength is not quite right, a technique referred to as compositional tuning was developed. Third, innovative laser designs are devised to produce laser sources at the requisite wavelengths.

Norman P. Barnes

Papers

Quantum efficiency measurements in Nd-doped materials

Diode-pumped all solid-state 2-µm power oscillator

Compositional wavelength tuning at the /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 11/2/ and /sup 4/F/sub 3/2//spl rarr//sup 4/F/sub 9/2/ transitions in Nd doped mixed apatite crystals

Solid-State Lasers For The Mid-Infrared Region

NASA lasers probe planets