Richard A. Myers

Enhancing near-infrared avalanche photodiode performance by femtosecond laser microstructuring

A processing technique using femtosecond laser pulses to microstructure the surface of a silicon avalanche photodiode (APD) has been used to enhance its near-infrared (near-IR) response. Experiments were performed on a series of APDs and APD arrays using various structuring parameters and poststructuring annealing sequences. Following thermal annealing, we were able to fabricate APD arrays with quantum efficiencies as high as 58% at 1064 nm without degradation of their noise or gain performance. Experimental results provided evidence to suggest that the improvement in charge collection is a result of increased absorption in the near-IR.

Commercialization of laser-induced breakdown spectroscopy for lead-in-paint inspection.

A study was undertaken to determine if laser-induced breakdown spectroscopy (LIBS) can be a practical and competitive alternative to x-ray fluorescence (XRF) methods for lead-in-paint inspection. Experiments in the laboratory confirmed that LIBS is suitable for detecting lead in paint at the hazard levels defined by federal agencies. Although we compared speed, function, and cost, fundamental differences between the XRF and LIBS measurements limited our ability to make a quantitative performance comparison. While the LIBS method can achieve the required sensitivity and offers a way to obtain unique information during inspection, the current component costs will likely restrict interest in the method to niche applications.

Geiger photodiode array for compact, lightweight laser-induced breakdown spectroscopy instrumentation.

The development of a unique spectrometer based on an array of Geiger photodiodes has been shown to enhance the performance of laser-induced breakdown spectroscopy (LIBS) instrumentation. These compact, silicon-based detectors eliminate the need for postamplification electronics, allow for the detection of single photons at room temperature, and do not require complex gating-timing circuitry. The detectors have dark-count rates of <500 Hz at room temperature and a good response from the UV to the near IR. Their high sensitivity makes them candidates for standoff analysis as part of a LIBS spectrum analyzer.

Recent advances in very large area avalanche photodiodes

The Avalanche Photodiode (APD) is a unique device that combines the advantages of solid state photodetectors with those of high gain devices such as photomultiplier tubes (PMTs). APDs have internal gain that provides a high signal-to-noise ratio. APDs have high quantum efficiency, are fast, compact, and rugged. These properties make them suitable detectors for important applications such as LADAR, detection and identification toxic chemicals and bio-warfare agents, LIDAR fluorescence detection, stand-off laser induced breakdown spectroscopy (LIBS), and nuclear detectors and imagers. Recently there have been significant technical breakthroughs in fabricating very large APDs, APD arrays, and position sensitive APD arrays (PSAPD). Signal gain of over 10,000 has been achieved, single element APDs have been fabricated with active area greater than 40 cm2, monolithic pixelated arrays with up to 28 x 28 elements have been fabricated, and position sensitive APDs have been developed and tested. Additionally, significant progress has been made in improving the fabrication process to provide better uniformity and high yield, permitting cost effective manufacturing of APDs for reduced cost.

UV-enhanced silicon avalanche photodiodes

Silicon avalanche photodiodes (APDs) fabricated through a deep diffusion process underwent a modified surface treatment in an attempt to improve their response in the ultraviolet region of the optical spectrum. After adjusting the doping profile in the near-surface region of the detectors, APDs were fabricated and tested at several wavelengths from ultraviolet to the near-infrared. At the target wavelength of 355 nm, the detector bandwidth was increased by a factor of 20 over devices fabricated without the modified surface treatment. Modest improvements in the internal quantum efficiency were also measured. Most importantly, the modified detectors maintained the high gain and low noise performance specifications that are hallmarks of traditional deep diffusion APDs.

Near-infrared enhanced position-sensitive avalanche photodiodes

A laser processing method was used to microstructure the surface of position-sensitive silicon avalanche photodiodes (PSAPDs) and enhance their near-infrared response. Following laser microstructuring and high-temperature annealing, experiments were performed on PSAPDs to determine their performance at 1064 nm. As a result of this processing method, we fabricated APDs with quantum efficiencies as high as 58% at 1064 nm. The enhanced near-infrared response has now been realized in both lateral effect and quadrant-type PSAPDs without altering their electronic noise, avalanche gain or position resolution. A near-infrared-enhanced PSAPD module with temperature control and position output was assembled and tested.

APD imaging probe for tritium surface contamination

We report on the development of a practical, easy-to-use, multi-element, solid-state instrument for detecting and imaging tritium contamination on surfaces. The innovation, which enables this instrumentation, relies on cutting-edge silicon avalanche photodiode (APD) array detector technology to provide an effective coverage area without compromising the overall sensitivity. We discuss the design and assembly of a prototype unit to monitor a surface area of over 900 mm2 while maintaining a spatial resolution of less than 4 mm. During tests at Los Alamos National Laboratories, we demonstrated tritium counting efficiencies of over 40% and established that this unit can be used to expedite established testing procedures by locating areas of potential activity or when combined with established swipe analysis.

Increased throughput single molecule detection of DNA

In this work, we present research in using confocal optical techniques with femtolitre focal volumes and obtain very high signal-to-noise and signal-to-background ratios for single molecule detection (SMD). We were able to achieve improved signal strength by using highly fluorescent quantum dots and nanopatterned substrates to obtain plasmon induced resonant fluorescence enhancement. A method to simultaneously using multiple excitation spots without the use of confocal apertures and an array of single photon sensitive Geiger mode avalanche photodiodes was used to increase the throughput of the detection system. Using this highly sensitive SMD system, we detect small quantities of synthetic DNA through hybridization eliminating the need of polymerase chain reaction.

Photon-counting spectrometer for elemental analysis using LIBS

Avalanche Photodiode (APD) arrays are being applied to Laser-Induced Breakdown Spectroscopy (LIBS) for elemental analysis with standoff detection capability. This instrument, which represents a valuable addition to planetary rover missions as well as Earth-based applications, benefits from the advantages common to both Geiger-mode and proportional APDs, which are solid-state detectors with virtually single-photon sensitivity, higher quantum efficiency than photomultiplier tubes or intensified CCDs, and rapid sub-nanosecond response speed. We have demonstrated LIBS detectability better than 770 parts-per-billion of sodium utilizing the photon-counting Geiger-mode APD. In a LIBS system, an APD array offers the unparalleled prospect of selecting in each channel the most appropriate temporal window for detecting the target species. In real-time detection systems, such as microfluidics-based fluorescence detection of bacterial spores, these compact, robust APD arrays promise portable hand-held instruments that utilize tight optical coupling.