Tunable IR diode laser

Absorption Spectroscopy of Combustion Gases Using a Tunable IR Diode Laser... 

Hanson, R. K., Kuntz, P. A., and Kruger, C. H., "High-Resolution Spectroscopy of Combustion Gases Using a Tunable IR Diode Laser" Applied Optics, 1977, 16, 2045. 

Successful concepts for "reaction-modulated" IR difference spectroscopy use the multiplex advantage of FTIR spectroscopy or the availability of high-intensity laser IR sources. A kinetic photometer using tunable IR diode lasers as sources for the mid-infrared has been developed in our laboratory and will be described elsewhere [6]. It covers the time-domain from approx. 500 nsec to some seconds. A second approach is time-resolved FTIR spectroscopy using a rapid-scanning interferometer, several scans can be recorded per second and the time-domain of slow reactions thus be covered [7]. The following schemes illustrate both concepts ... 

Constants of the ground state and the v = 1 vibrational state were measured using a tunable IR diode laser in the range of the fundamental vibration band and the Zeeman modulation of the absorption lines. The true values depend on the unobserved state. From line positions, only effective B values, defined as B (2ri3 ) = Bv(1 + Bv/A) (A = fine structure constant, see p. 68) can be deduced [1,4], from which the following constants were derived [4] taking A = -177.3cm"i [1] ... 

The complete set of the three normal vibrations (0-0 stretch), vg (bend), and vg (0-F stretch), has only been observed by IR absorption of the radical isolated in various matrices. In the gas phase, the band center (at 1489 cm" ) was found with a Fourier transform IR spectrometer [2]. Only a small section of the band around 1480 cm" was observed by tuning the Zeeman splittings of vibration-rotation transitions to selected lines of a CO laser (laser magnetic resonance, LMR) [1]. Vg = 579.31839 0.00035 cm (band origin) was measured with a tunable IR diode laser and using Zeeman modulation of absorption lines [3]. 

R.K. Hanson, P.A. Kuntz, C.H. Kruger High-resolution spectroscopy of combustion gases using a tunable IR diode laser. Appl. Opt. 16, 2045 (1975)... 

Recently, we have analyzed the molecular processes upon Qg electron transfer in Rb, sphaeroides RC by time-resolved IR spectroscopy using a kinetic photometer with tunable IR diode lasers (Hienerwadel et al, 1992). We were able to identify rapid (<0.5 fiscc) IR absorbance changes arising from the P->P" " or the Q transition, correlating in frequency and amplitude with P /P and Qa Qa stationary spectra. In addition, transient —120 fisec signals could be characterized which arise either from the or the Qg Qg transitions. These signals... 

The pump source in the dispersive experiment is typically a nanosecond laser the probe source can be broadband IR light from a globar or tunable IR light from a CO laser or a semiconductor diode laser. Although CO and diode lasers can produce... 

FIGURE 11.31 Comparison of gaseous HN03 measurements made simultaneously in Claremont, California, on two different days using FT-IR shown as with error bars and by a filter pack (FP), a difference denuder (DD), an annular denuder (AD), and tunable diode laser spectroscopy (TDLS) (adapted from Hering et al., 1988). 

Werle, P., R. Muecke, and F. Slemr, Development of a Prototype IR-FM Absorption Spectrometer Design Criteria and System Performance, in Monitoring of Gaseous Pollutants by Tunable Diode Lasers (R. Grisar, H. Boettner, M. Tacke and G. Restelli, Eds.), pp. 169-182, Kluwer Academic, Dordrecht, The Netherlands, 1992. 

As mentioned in the introduction, a major advantage that Fourier transform spectroscopy has over laser spectroscopy is that it is straightforward to record the entire spectrum of a species at once. Diode lasers in the infrared are not continuously tunable and have mode gaps which can only be filled by switching diodes. Many ultraviolet lasers are not continuously tunable either. Tunable difference frequency methods and diode lasers involve much longer scan times than are necessary with a Fourier transform device. For example, the Bomem DA3.002 can scan a bandwidth of 100 or more wavenumbers in the mid-IR at a resolution of 0.005 cm-1 in less than 3 minutes. A diode laser which scans in 20 MHz steps may require more than a day to scan the same spectral region. 

CO Internal Excitation. As stated above, we measured nascent CO V, R excitation following reaction (1) using time-resolved IR absorption spectroscopy, with a tunable diode laser as the probe. Details of the experimental... 

Several existing instruments, including suction pyrometers, IR spectrometers, and acoustic pyrometers are already in regular use for combustion gas temperature measurement. However, conventional sensors are often subject to errors due to disturbances caused by the presence of the probe, ill-defined spatial resolution, and slow response time. Tunable Diode Laser (TDL) absorption spectroscopy seeks to overcome limitations sometimes associated with these traditional instruments. This technique is of particular interest for industrial combustion applications since it provides the following features ... 

Widely used techniques to produce reactive species such as 1 or 2 are dc glow discharges coupled to sensitive high-resolution spectroscopic techniques such as millimeter wave (mmw), microwave (mw), or tunable diode laser (TDL) IR spectroscopy.However, even in cooled electric discharges, not only the precursor, but also the target species thus formed, are destroyed rather unselectively, and their concentrations in discharges are often very low. ... 

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