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.

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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

Injection seeding of an AgGaSe2 mid infrared optical parametric oscillator using a continuous wave HeNe laser operating at 3.39 µm has been demonstrated. A measurement of the resulting spectral bandwidth, 0.001 µm, was resolution limited. Pulse evolution time intervals were found to be significantly shorter when injection seeding was in effect while the efficiency was found to be significantly higher.

Injection-Seeded Optical Parametric Oscillator

The laser performance of Nd:Cr:GSGG and Nd:YAG was investigated and compared for laser efficiency, thermal focusing, and depolarization effects. Laser efficiency was studied for Nd:Cr:GSGG and Nd:YAG under similar conditions. Laser efficiency was measured as a function of electrical energy and output mirror reflectivity. Maximum laser efficiency was calculated by determining the losses in the laser cavity. Thermal focusing and birefringence loss of Nd:Cr:GSGG and Nd:YAG have been examined by varying the average pump power. The average pump power changed by adjusting both the energy per pulse and the pulse-repetition frequency. Substantial thermal focusing differences for Nd:Cr:GSGG are explained.

Laser performance, thermal focusing and depolarization effects in Nd:Cr:GSGG and Nd:YAG

A quasi four-level solid-state laser is provided. A laser crystal is disposed in a laser cavity. The laser crystal has a LuAG-based host material doped to a final concentration between about 2% and about 7% thulium (Tm) ions. For the more heavily doped final concentrations, the LuAG-based host material is a LuAG seed crystal doped with a small concentration of Tm ions. Laser diode arrays are disposed transversely to the laser crystal for energizing the Tm ions.

/pdf/quasi-four-level-tm-luag-laser-3xay4dmff8.pdf

Quasi four-level Tm:LuAG laser

We observed the tunability of a 946-nm Nd:YAG microchip laser by using a double-cavity configuration. We shifted the lasers wavelength from 938 to 946 nm by changing the thickness of the air gap. In addition, differences in reflectivity of the output mirror yielded the tunable range of the 946-nm band, with the center oscillation wavelength maintained at 946.1 nm.

Tunability of a 946-nm Nd:YAG microchip laser by use of a double-cavity configuration

A reliable Ho:YLF laser system has been successfully developed. Problems encountered in laser‐rod and support‐system design were unique and most difficult to solve. These problems include holding a fragile laser rod having nonisotropic thermal expantion with vacuum tight seals which can be thermally cycled. Experimentally proven solutions are described which should help others in developing new solid‐state laser systems.

Norman P. Barnes

Papers

Injection-Seeded Optical Parametric Oscillator

Laser performance, thermal focusing and depolarization effects in Nd:Cr:GSGG and Nd:YAG

Quasi four-level Tm:LuAG laser

Tunability of a 946-nm Nd:YAG microchip laser by use of a double-cavity configuration

Liquid nitrogen cooled laser rod holder design