A transportable prototype Faraday rotation spectroscopic system based on a tunable external cavity quantum cascade laser has been developed for ultrasensitive detection of nitric oxide (NO). A broadly tunable laser source allows targeting the optimum Q _3/2 (3/2) molecular transition at 1875.81 cm ⁻¹ of the NO fundamental band. For an active optical path of 44 cm and 1-s lock-in time constant minimum NO detection limits (1σ) of 4.3 parts per billion by volume (ppbv) and 0.38 ppbv are obtained by using a thermoelectrically cooled mercury–cadmium–telluride photodetector and liquid nitrogen-cooled indium–antimonide photodetector, respectively. Laboratory performance evaluation and results of continuous, unattended monitoring of atmospheric NO concentration levels are reported.

Observations of the jet-cooled infrared spectrum of CH₃O in the CH stretching region have been extended, down to 2756 cm⁻¹ and up to 3003 cm⁻¹. In the lower frequency extension, a single vibronic band has been assigned. In the higher frequency region, the spectrum becomes complex above 2900 cm⁻¹ and remains so until near 2970 cm⁻¹ where it rapidly becomes sparse. Including the single vibronic band previously reported, a total of four bands have been assigned. Two bands including the original one follow a perpendicular ΔP = +1 rotational selection rule and the other two bands follow a parallel ΔP = 0 selection rule. In addition to these in the congested region between 2900 and 2970 cm⁻¹, ten isolated sub-bands (two P″ = −1/2, two P″ = +1/2, and six P″ = +1.5) have been assigned, but it has so far not been possible to connect these together to form bands. Taken together these observations suggest that there are strong vibronic couplings between the two CH stretching vibrations and the overtone and combination levels in the region.

We report the results of our efforts to increase the infrared output power from a cw difference frequency generation source based on the nonlinear material AgGaS₂ for use in infrared kinetic spectroscopy. Experimental and theoretical infrared conversion efficiencies are compared as a function of pump power, signal power, and focusing conditions. The predicted and observed IR yields agree well for the unfocused beam; however, the agreement is poor (experimental conversion a factor of 3 to 5 less than theory) for all focused conditions. The highest IR output powers obtained corresponded to experimental conditions that are slightly overfocused compared to the theoretical optimum. Thermal loading of the AgGaS₂ decreases the parametric conversion efficiency when the power in one of the input lasers beams exceeds approximately 800 mW. Infrared powers of 10 to 30 (mu) W have been achieved near 5.2 micrometers . Future improved crystals should yield powers at the AP 500-(mu) W level.

The field of fluorescence imaging for biomedical applications has undergone a dramatic expansion over the past $20\text{years}$ . It is the most rapidly expanding technique employed today, in both the medical and biological sciences,^{1, 2, 3, 4, 5, 6, 7, 8, 9} a fact that is spurring the development of more sophisticated microscopes^{10, 11, 12, 13, 14} and wide-field imagers.¹⁵ The availability of hundreds of fluorescent labels^{16, 17} with known excitation and emission curves and well-understood biological structure targets has accelerated the application of fluorescence microscopy in both clinical laboratories and research. These developments allow great flexibility and specificity in what can be imaged. Many fluorescent dyes are compatible with living organisms, making in vivo imaging possible. In particular, functional imaging of a biological process can be achieved^{3, 4, 5, 18} by selecting a fluorescent label that attaches to a dynamic structure of interest within the sample.