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

Tunable 4-10 μm Infrared Radiation for Remote Sensing Applications

Challenges for current spectroscopy: detection of security threats

Tm:YAG lasers and second harmonic generation

Remote sensing using mid-infrared wavelength has many applications in pollution surveillance and atmosphere studies. However, high gain, low noise detectors or single photon counters are not available in the mid-infrared wavelength range. One approach to obtain single-photon detection in mid-infrared wavelength is to convert the mid-infrared radiations into visible/near-infrared wavelengths where high efficiency and low dark current detectors are easily available. In this paper, the up-conversion of mid-infrared radiations based on the quasi-phase matching condition of periodically poled lithium niobate (PPLN) is investigated. The bandwidth and efficiency are the two essential parameters for the up-conversion process. The optimal pump wavelength λ laser o and PPLN period Λ can be determined from conservations of energy and momentum. Once the λ laser o and Λ are defined, the spectral bandwidth corresponding to the full width at half maximum of frequency up-conversion can be calculated. The spectral bandwidth of mid-infrared radiations can exceed 130 nm for a 25 mm PPLN crystal when the pump laser operates in the optimum wavelength. It is wide enough to cover both the on and off wavelengths of the species of interest in a Differential Absorption Lidar. The maximum up-conversion bandwidth usually corresponds to the longest PPLN period allowed by the quasi-phase matching condition. The conversion efficiency increases with the pump laser intensity. Both the external cavity pumping approach with cavity locking technique and the intra-cavity pumping approach can greatly increase the up-conversion efficiency.

Nonlinear frequency up-conversion for mid-infrared single-photon detection

A description of a frequency doubled, double pulsed Nd:YAG laser that is to be used to pump an injection locked Ti:Sapphire power oscillator is presented. These two lasers make up the transmitter portion of the Lidar Atmospheric Sensing Experiment (LAWSE) instrument. LASE is a Lidar/DIAL experiment that is to measure water vapor in the troposphere. By utilizing the twin concept, both pulses can be produced with a single laser system, thereby minimizing cost, size, and weight. Alignment problems associated with having two separate lasers each produce one of the twin pulses are also alleviated. The LASE transmitter consists of a doubled pulsed Nd:YAG laser that will pump a Ti:Sapphire power oscillator that will be injection-locked by a diode laser. The wavelength of the Ti:Sapphire output will be tunable from 813 to 818 nm. A performance summary of the pump laser is given. The data verify that the pump laser can meet the performance requirements to pump the Ti:Sapphire power oscillator.

Norman P. Barnes

Papers

Tunable 4-10 μm Infrared Radiation for Remote Sensing Applications

Challenges for current spectroscopy: detection of security threats

Tm:YAG lasers and second harmonic generation

Nonlinear frequency up-conversion for mid-infrared single-photon detection

Characterization of a Nd:YAG doubled pulsed laser system