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

A tunable continuous-wave (CW) intracavity pumped periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) has been developed where a diode-pumped ring-cavity Nd:YAG laser is used as the pumping source. The idler tunable range from 2.3 μm to 3.9 μm with linewidth less than 15 MHz has been demonstrated. The slop efficiency of the idler output versus the diode pump power is ~ 5.6%. The idler output power at 3.4 μm reaches 370 mW when the diode output power is 21.5 W. The PPLN OPO will be applied to seed ZnGeP2 OPO pumped by a Tm:Ho:YLF laser (λ=2.05 μm). The ZnGeP2 OPO can be tuned between 3-10.5 μm. Combined PPLN OPO and ZnGeP2 OPO, the tunable range covers the strong absorption lines of most atmospheric pollutants, and overlaps the mid-infrared atmospheric windows of 3.4-5 μm and 8-13 μm. The mid-infrared emission source is a potential lidar transmitter for remote sensing applications.

Tunable mid-infrared coherent source for lidar: CW OPO

Global wind measurement is a key component of weather prediction. Coherent wind lidar provides excellent wind profile measurement sensitivity and accuracy through the use of heterodyne detection technique. A high pulse energy, high beam quality, very narrow linewidth laser is essential for successful coherent wind detection. We have developed an eye- safe all solid state Ho:Tm:YLF power oscillator with ring configuration to be used as coherent lidar transmitter. It achieved an optical to optical efficiency of 0.03. A Q- switched output energy as high as 109 mJ at 6 Hz, with a pulse width of 170 ns is obtained. The resonator alignment sensitivity, heat dissipation efficiency and polarization extinction ratio are all characterized for space application lidar. Laser performance as a function of laser rod temperature and pump intensity has also been investigated. The high power and high beam quality of this laser make it well suited for use as a coherent wind lidar transmitter on a space platform.

Eye-safe all-solid state laser for coherent wind lidar in space

Laser Operation of 1.76 µm Pumped Ho:Tm:LuAG

A Q-switched 2-µm oscillator and a double-passed amplifier based on recently identified efficient Ho:Tm:LuLF laser material were developed. 380-mJ single pulse energy and 630-mJ double pulse energy have been achieved with high efficiency

Diode-pumped Ho: Tm: LuLF laser oscillator and laser amplifier at 2 µm

We report a singly resonant, 2.05 µm pumped Zinc Germanium Phosphide optical parametric oscillator with high pulse energy at an energy conversion efficiency of 27.5%. It generates up to 17.3mJ with the tunability over 4.3-10.1µm.

Norman P. Barnes

Papers

Tunable mid-infrared coherent source for lidar: CW OPO

Eye-safe all-solid state laser for coherent wind lidar in space

Laser Operation of 1.76 µm Pumped Ho:Tm:LuAG

Diode-pumped Ho: Tm: LuLF laser oscillator and laser amplifier at 2 µm

Parametric generation of tunable mid-infrared radiation