Diffusion Diode lasers

Fox, D. L L. Stockburger, W. Weathers, C. W. Spicer, G. I. Mackay, H. I. Schiff, D. J. Eatough, F. Mortensen, L. D. Hansen, P. B. Shepson, T. E. Kleindienst, and E. O. Edney, Intercomparison of Nitric Acid Diffusion Denuder Methods with Tunable Diode Laser Absorption Spectroscopy, Atmos. Environ., 22, 575-585 (1988). 

Wall-coated flow tube reactors have been used to study the uptake coefficients onto liquid and solid surfaces. This method is sensitive over a wide range of y (10" to 10 1). For liquids this method has the advantage that the liquid surface is constantly renewed, however if the uptake rate is fast, the liquid phase becomes saturated with the species and the process is limited by diffusion within the liquid, so that corrections must be applied [70,72,74]. Many experiments were designed to investigate the interaction of atmospheric species on solid surfaces. In this case the walls of the flow tube were cooled and thin films of substrate material were frozen on the wall. Most of the reaction probabilities were obtained from studies on flow tubes coated with water-ice, NAT or frozen sulfate. Droplet train flow tube reactors have used where liquid droplets are generated by means of a vibrating orifice [75]. The uptake of gaseous species in contact with these droplets has been measured by tunable diode laser spectroscopy [41]. 

If the 3 u) pulse of mode-locked Nd YAG laser and the picosecond continuum are used as an excitation and a monitoring pulses, respectively, just as in the transmittance and diffuse reflectance laser photolyses, the time-resolution should be improved up to 10 ps. In this case the pulse width of the picosecond continuum is less than 20 ps, so that the multichannel diode array without gating function was used. A demonstration experiment was performed for poly(methyl methacrylate) film containing 15 wt% benzophenone. The transient absorption spectrum at about 650 ps obtained with 6 = 59° is... 

Figure C2. 16.ll illustrates the evolution of the threshold current density of diode lasers with the structure of the recombination region within the p-n jimction, known as the active region. The early diode lasers were based on GaAs homojunctions. Their large threshold current densities resulted from poor carrier confinement and large effective active region thickness. This is because the diffusion length of electrons is fairly long in most of the semiconductors discussed here, of the order of several micrometres. A very high threshold current density limits operation to short pulses and ciyogenic temperatures.

An important application of multiplexed multidetector systems is diffuse opti-eal tomography (DOT). In DOT several pieoseeond diode lasers are multiplexed into the input of a fibre switeh. The multiplexed lasers are switched conseeutively into a large number of optieal fibres whieh deliver the light to the sample. The... 

An instrument for optical biopsy of bones based on a diode laser and a single TCSPC channel is described in [151, 152]. Other instruments use a tuneable synchronously pumped dye laser and a Ti Sapphire laser [414]. The lasers are switched into a single source fibre by a fibre switch. A single TCSPC channel records the diffusely reflected light and a reference signal split off from the source fibre. 

A diode laser sends a beam of 100 ps pulses to the target. The repetition rate of the laser pulses is 50 MHz, the average power 0.5 mW. A 20-cm (8-ineh) telescope (Meade LX90 EMC) is used to collect the photons from the target. The fluorescence and the reflected light are separated by a dichroie mirror and a 700 15 nm bandpass filter and detected simultaneously by two individual detectors. Consequently, detector 1 detects the diffusely reflected laser, deteetor 2 the fluorescence of the leaves. 

Kalisky Y, Kravchik L, Kokta MR (2004) Performance of diode-end-pumped Cr, Nd YAG self-Q-switched and Nd YAG/Cr YAG diffusion bonded lasers. Opt Mater 24 607-614... 

Miller JH. Elreedy S. Ahvazi B. Woldu F and Hassanzadeh P (1993) Tunable diode-laser measurement of carbon monoxide concentration and temperature in a laminar methane-air diffusion flame. Applied Optics 32 6082-6089. 

At Waterloo, Gough, Miller, and Scoles have generated a molecular beam of N20 N20. A diode laser beam was then scanned over the V3 mode to produce N20(001) N20(000). [The notation (vx,V2,V3) labels the vibrational levels involving the chemical bonds of N2O.] They reported the lifetime of this vibrationally excited complex to be in the range 10 to 10 s. The upper limit was established from the time of flight from the place of irradiation to the detector, and the lower limit was obtained by assuming that the total width of the diffuse absorption bond was due to predissociation. 

Samples were characterized by FTIR spectroscopy with a Perkin Elmer (Spectrum BX) spectrometer using KBr pressed disks as matrices. The DRIFT experiments were carried out with a Broker IFS 55 spectrometer equipped with a Thermo Spectra Tech reacting cell. UV-vis Diffuse Reflectance spectra were recorded on a Perkin Elmer Lambda 45 spectrophotometer equipped with a diffuse reflectance attachment. Raman spectra were collected with Perkin Elmer system 2000 NIR FT-Raman using as excitation radiation the 5th harmonic of a diode pumped Nd YAG laser (1065 nm). 

Figure 8.7. Delayed fluorescence and diffuse reflectance transient absorption spectroscopy on scattering substrates. Example terthicnyl on silica gel excited with = 354 nm (neodymium/yttrium-aluminum-garnet) (Nd/YAG) laser pulse of 10 nsec, 20 mj), recorded with a gated diode array spectrometer.

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