Balanced Ratiometric Detection Research Articles

Ratiometric widefield imaging with spectrally balanced detection.

Ratiometric imaging is an invaluable tool for quantitative microscopy, allowing for robust detection of FRET, anisotropy, and spectral shifts of nano-scale optical probes in response to local physical and chemical variations such as local pH, ion composition, and electric potential. In this paper, we propose and demonstrate a scheme for widefield ratiometric imaging that allows for continuous tuning of the cutoff wavelength between its two spectral channels. This scheme is based on angle-tuning the image splitting dichroic beamsplitter, similar to previous works on tunable interference filters. This configuration allows for ratiometric imaging of spectrally heterogeneous samples, which require spectral tunability of the detection path in order to achieve good spectrally balanced ratiometric detection.

Advanced Photonic Sensors Based on Interband Cascade Lasers for Real-Time Mouse Breath Analysis.

A multiparameter gas sensor based on distributed feedback interband cascade lasers emitting at 4.35 μm and ultrafast electro-spun luminescence oxygen sensors has been developed for the quantification and continuous monitoring of 13CO2/12CO2 isotopic ratio changes and oxygen in exhaled mouse breath samples. Mid-infrared absorption spectra for quantitatively monitoring the enrichment of 13CO2 levels were recorded in a miniaturized dual-channel substrate-integrated hollow waveguide using balanced ratiometric detection, whereas luminescence quenching was used for synchronously detecting exhaled oxygen levels. Allan variance analysis verified a CO2 measurement precision of 1.6‰ during a 480 s integration time. Routine online monitoring of exhaled mouse breath was performed in 14 mechanically ventilated and instrumented mice and demonstrated the feasibility of online isotope-selective exhaled breath analysis within microliters of probed gas samples using the reported combined sensor platform.

Modified balanced ratio metric detection system used for high sensitive vapor detection

A modified balanced ratio metric detection (BRD) system was proposed and applied in trace measurement of water vapor. Three features, including proportion of alternating current (AC) and direct current (DC) signals, environment temperature and light intensity ratio have been stated. Their influences on measured result have been analyzed. Meanwhile, techniques including adding filter, using integrated transistor and light intensity ratio adjustment and their effects for measurement improvement have been discussed. The absorption line was chosen at 1368.597nm and the path length was 10cm. With application of the above techniques, an accuracy of 5ppm for water vapor concentration has been achieved.

Reliability analysis and comparison of demodulation methods for dual-beam wavelength-modulation spectroscopy water vapor detection

Subtraction, division, and balanced ratiometric detection (BRD) are three extensively used demodulation methods for dual-beam wavelength-modulation trace gas detection. However, reliability comparisons among these methods under changing environmental conditions were rarely researched. In this paper, the influences of ambient temperature and bend loss of fibers are analyzed in detail, and the reliabilities of the subtraction, division, and BRD methods are quantitatively compared for the first time to our knowledge. When the ambient temperature is increased by 1°C, the deviation of the division method is only 0.29%, which obviously outperforms the subtraction method (2.90%) and the BRD method (0.55%). Furthermore, a concept, "power fluctuation rejection ratio," is introduced to compare the suppression effects of the subtraction, division, and BRD methods on the laser light source power fluctuation. The study results demonstrate that the division method provides better reliability when the ambient temperature or bending loss is varied. The validity and reliability are fully verified by the fact that the experimental results give good agreement with the theoretical simulation.

Interband cascade laser–based sensor for ambient CH<sub>4</sub>

We demonstrate a mid-IR semiconductor laser-based absorp- tionspectrometerforfieldmeasurementsofambientCH4.Thefieldsensor uses a type II quantum cascade laser (or interband cascade laser, ICL) operating near 3.3 μm to monitor a well-isolated line in the ν3 fundamental band of CH4. The ICL operates in cw mode at cryogenic temperatures. The sensor uses a multipass cell that provides an optical path of ∼7mwith a 0.25-m base path. Thermoelectrically cooled InAs detectors are used along with balanced ratiometric detection to achieve a precision of 15 ppbv for a 60-s integration time. Several successful field demonstrations are carried out at sites maintained by the University of New Hampshire.

Application of balanced detection to absorption measurements of trace gases with room-temperature, quasi-cw quantum-cascade lasers

Distributed-feedback quantum-cascade (QC) lasers are expected to form the heart of the next-generation mid-IR laser absorption spectrometers, especially as they are applied to measurements of trace gases in a variety of environments. The incorporation of room-temperature-operable, single-mode QC lasers should result in highly compact and rugged sensors for real-world applications. We report preliminary results on the performance of a laser absorption spectrometer that uses a QC laser operating at room temperature in a quasi-cw mode in conjunction with balanced ratiometric detection. We have demonstrated sensitivities for N(2)O [10 parts in 10(6) volume-mixing ratio for a 1-m path (ppmv-m)] and NO [520 parts in 10(9) volume-mixing ratio for a 1-m path (ppbv-m)] at 5.4 mum. System improvements are described that are expected to result in a 2 orders of magnitude increase in sensitivity.

Determination of singlet-oxygen generator efficiency on a 10-kW class supersonic chemical oxygen-iodine laser (RADICL)

With the advent of the Air Force Airborne Laser program, the emphasis of chemical oxggen-iodine laser (COIL) research has shifted toward improving the overall efficiency. A key component of the COIL is the singlet-oxygen generator (SOG). To assess the efficiency of the SOG, an accurate method of determining the yield of O/sub 2/(a/sup 1//spl Delta//sub g/), [O/sub 2/(a/sup 1//spl Delta//sub g/)]/[O/sub 2/(total)] where [O/sub 2/(total)]=[O/sub 2/(a/sup 1//spl Delta//sub g/)]+[O/sub 2/(X/sup 3//spl Sigma//sub g//sup -/)], has been developed. Absorption measurements of ground-state oxygen utilizing the magnetic-dipole transition, O/sub 2/(X/sup 3//spl Sigma//sub g//sup -/)/sub (/spl nu/=0)//spl rarr/O/sub 2/(b/sup 1//spl Sigma//sub g//sup +/)/sub (/spl nu/=0)/ centered at 762 nm, have been obtained using a scanning diode laser in conjunction with a multiple-pass Herriott cell and balanced-ratiometric detection on the 10-kW class supersonic COIL (RADICL). A series of experiments was designed and conducted to test the efficiency of the SOG under various conditions.