Diode laser spectrometer

Spaink, H. A., and Lub, T. T., Improvement of the Performance of a Diode-Laser Spectrometer by Using Sweep Averaging and Numerical Data Processing, Analytica Chimica Acta 241, 1990, 83-94. 

A balloon-borne, open path, tunable diode laser spectrometer (21) provides a particularly elegant technique that combines the advantages of in situ and remote sampling. The radiation absorption path is defined by the laser on the balloon gondola and a retro reflector suspended up to 500 m below. Thus, a well-defined parcel of air is analyzed and the effects of sampling inlets are avoided. NO, NO , HN03, N20, and 03 have been measured simultaneously (22). 

A diode laser spectrometer. In this case, if the laser is a tunable laser, there are only two critical components the tunable laser and the detector. Typically, the enabling technology is the laser, which in this mode acts as the light source and the wavelength selection device. 

More recently, Vogt et al. (1984 b) recorded the NN stretching band of gaseous diazomethane by means of an interferometer and a tunable diode laser spectrometer. With that equipment, the structure of the band was resolved for the first time, and nine subbands were analyzed. The recording was made with a resolution of 0.07 cm ... 

The spectrum of the out-of-plane band of thiophene centered at 712 cm has been measured in Doppler-limited resolution with a diode-laser spectrometer and with a high-resolution FT spectrometer <93ZN(A)1193>. The band at 712 cm which is the Ui, band <65SA689>, is of symmetry Bi. 

The fundamental absorption band of PH in its ground state X was observed at high resolution using a tunable diode laser spectrometer eighteen lines betwen 2224.4125 and 2107.8160 cm" (4.50 to 4.74 pm) have been identified as P-branch transitions with N" = 3 to 7 and 9, where each transition exhibits the fine-structure triplet splitting due to AJ = AN transitions between the three sublevels (J = N +1, N, N -1) of the respective rotational levels N" and N. Two further lines at 2292.1918 and 2308.1542 cm" (-4.3 pm) have been identified as the R-branch transitions with N", J " = 0,1 and 1,0. Hyperfine splitting could not be resolved. The analysis, which included rotational and centrifugal distortion effects as well as spin-spin... 

Example 10.1 With a diode laser spectrometer and a multipass absorption cell (Fig. 10.1) NO2 concentrations down to the 50-ppt level in air were detected on a vibrational-rotational transition at 1900 cm NO concentrations down to 300 ppt, while for SO2 at 1335 cm a sensitivity limit of 1 ppb was reached [1371]. 

For such absorption measurements infrared lasers can be used which coincide with vibrational-rotational transitions of the investigated molecules (CO2 laser, CO laser, HF or DF lasers, etc.). Particularly useful are tunable infrared lasers (diode lasers, color-center lasers, or optical parametric oscillators, Vol. 1, Sect. 5.7), which may be tuned to selected transitions. The usefulness of diode lasers has been demonstrated by many examples [1451]. For instance, with a recently-developed automated diode laser spectrometer, which is tuned by computer control through the spectral intervals of interest, up to five atmospheric trace gases can be monitored in unattended operation. Sensitivities down to 50 ppt for NO2 and 300 ppt for NO have been reported [1371]. 

G. Schmidtke, W. Kohn, U. Klocke, M. Knothe, W.J. Riedel, H. Wolf, Diode laser spectrometer for monitoring up to five atmospheric trace gases in unattended operation. Appl. Opt. 28, 3665 (1989)... 

Kormann R, Muller H, Werle P. 2001., Eddy flux measurements of methane over the fen Mumauer Moos , 11° 11 E, 47°39 N, using a fast tunable diode laser spectrometer . Atmos. Environ. 35(14) 2533-2544. 

A complete commercial diode laser spectrometer for convenient use in infrared spectroscopy is depicted in Fig. 5.71. 

Fig. 5.71. Schematic diagram of a diode laser spectrometer tunable from 3 to 25 xm with different diodes, (courtesy of Spectra-Physics)...

Fig.9.3. (a) Principle of laser absorption spectroscopy, (b) A diode laser spectrometer (Courtesy Spectra Physics)... 

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