We present the combination of electrochemiluminescence imaging with enzyme immunoassay for the highly sensitive detection of protein/polypeptide residues in latent fingermarks. This technique provides an effective method for fingermark detection that enables both identification of an individual and recognition of the secretions in the human perspiration.
CdZnTe detectors have been under development for the past two decades, providing good stopping power for gamma rays, lightweight camera heads and improved energy resolution. However, the performance of this type of detector is limited primarily by incomplete charge collection problems resulting from charge carriers trapping. This paper is a review of the progress in the development of CdZnTe unipolar detectors with some data correction techniques for improving performance of the detectors. We will first briefly review the relevant theories. Thereafter, two aspects of the techniques for overcoming the hole trapping issue are summarized, including irradiation direction configuration and pulse shape correction methods. CdZnTe detectors of different geometries are discussed in detail, covering the principal of the electrode geometry design, the design and performance characteristics, some detector prototypes development and special correction techniques to improve the energy resolution. Finally, the state of art development of 3-D position sensing and Compton imaging technique are also discussed. Spectroscopic performance of CdZnTe semiconductor detector will be greatly improved even to approach the statistical limit on energy resolution with the combination of some of these techniques.
High finesse hollow-core photonic bandgap fiber (HC-PBF) resonating Fabry-Perot gas cells are presented. These gas cells are made with a piece of HC-PBF sandwiched by two single mode fibers with mirrored ends. A HC-PBF cavity made with 6.75-cm-long HC-1550-06 fiber achieved a cavity finesse of 128, corresponding to an effective optical path length of ~5.5 m. Experiment with a 9.4-cm-long Fabry-Perot gas cell with a finesse of 68 demonstrated a detection limit of 7 p.p.m. acetylene. Compared with a single-path non-resonating HC-PBF, the use of a high finesse resonating HC-PBF cavity can reduce significantly the effect of modal interference on gas detection and improve the detection sensitivity. The cavity-enhanced HC-PBF gas cells enable stronger light-gas interaction and can be used to develop all-fiber gas sensors with high sensitivity and fast response.
We report an all-optical fiber photoacoustic gas sensor with a graphene nano-mechanical resonator as the acoustic detector. The acoustic detector is a Fabry-Perot interferometer formed by attaching a 100-nm-thick, 2.5-mm-diameter multilayer graphene diaphragm to a hollow cavity at the end of a single mode optical fiber. By operating at one of the mechanical resonances of the diaphragm, the sensitivity for acoustic detection is enhanced and a noise equivalent minimum detectable pressure of 0.63 μPa/Hz 1/2 at 4.3 kHz is demonstrated. Detection of acetylene gas is demonstrated with a distributed feedback semiconductor laser tuned to the P(9) absorption line of acetylene and a lower detection limit of 119.8 parts-per-billion (ppb) is achieved with 123.9 mW pump power. Theoretical analysis shows that by increasing the Q-factor of the resonator, which may be achieved by operating at low gas pressures, ppb level gas detection is possible. The all-fiber photoacoustic gas sensor is immune to electromagnetic interference, safe in flammable and explosive environment, and would be ideally suited for remote, space-limited applications and for multipoint detection in a multiplexed fiber optic sensor network.
We have successfully fabricated a series of sampled fiber Bragg gratings with easily adjustable sampling periods and duty cycles using an 800 nm femtosecond laser point-by-point inscription. The thermal stability of the fabricated fiber gratings was investigated using isochronal annealing tests, which indicated that the fiber gratings are capable of maintaining high reflectivity at temperatures of up to 1000°C for 8 h. This demonstrates the potential of the developed sampled fiber Bragg gratings for use in multi-wavelength fiber lasers and a variety of high temperature applications.
An all-optical fiber photoacoustic gas sensor with double resonant signal enhancement is presented. The sensor uses a fiber-tip graphene nano-mechanical resonator operating at one of its resonances as the acoustic detector and a micro-acoustic resonant tube, whose resonant frequency is matched to that of the graphene resonator, as the PA gas cell. Compared with the single resonant detection with a graphene resonator, a five-fold signal enhancement is achieved. With 138 mW pump power and 1 second lock-in time constant, a noise equivalent concentration of ~25 ppb C2H2 is achieved, corresponding to a normalized noise equivalent absorption of 1.29x10 -8 cm -1 WHz -1/2 .
Light-gas interaction can be enhanced by using disordered porous materials because multiple random scattering increases light intensity near the surface of the material. Here we report signal enhancement of photoacoustic gas spectroscopy with disordered porous ceramics. The amplitude and frequency characteristics of photoacoustic signal due to gas absorption in disordered materials are modeled theoretically. Experiment with a porous AlO sample demonstrates photoacoustic signal enhancement of ∼4 times at 5 kHz.
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