Diode Laser Spectroscopic Monitoring of Trace Gases

Abstract

Modern diode laser spectroscopy is becoming an important and a more widely used tool for detection and measurement of trace gases. The change is driven by the recent advances in diode laser technology and diode laser frequency conversion techniques, which now push the limits of emission wavelength, output power, operating temperature, miniaturization, and cost. Basic features of the diode laser now find new, interesting, and unique use in well‐established laboratory and field applications related to trace‐gas detection, and in some instances even transform the traditional spectroscopic methods. It is the purpose of this chapter to familiarize the reader with the key elements of diode laser technology and analytical methods used in diode laser spectroscopy.

Equivalent path lengths in an integrating cavity: comment

“…(15), an important error is introduced. We found 12 references [2][3][4][5][6][7][8][9][10][11][12][13] to this paper, and 3 of them [3,6,13] make explicit use of the expressions that are in error.…”

Cavity-based absorption spectroscopy techniques

“…For example, tunable diode laser absorption spectroscopy (TDLAS) (Schiff et al , 1994;Tacke et al ., 2000;Tittel and Petrov, 2000;Curl and Tittel, 2002;Tittel et al ., 2003Tittel et al ., , 2008Lackner, 2007;Markus, 2008;Werle et al , 2008;Frish et al , 2010) is a signifi cant context, particularly in the mid-infrared wavelength region where molecules can be identifi ed and characterised through their quantised fundamental vibrations and associated rotational energy levels. Also, communications-band diode lasers that operate in the near-infrared region are conveniently available to access molecular vibrational overtone and combination bands; however, these bands typically have much weaker absorption coeffi cients than corresponding mid-infrared fundamental bands.…”

“…They include: open-path laser absorption spectroscopy, in which a laser beam passes from a distant retro-refl ector and back to a detector that is co-located with the laser (Schiff et al , 1994;Platt, 1994Platt, , 2000Platt et al , 2012); LIDAR ( li ght d etection a nd r anging) and its dual-channel modifi cation DIAL, in which the temporal or phase characteristics of light provide an optical ranging capability (Grant and Menzies, 1983;Killinger et al , 1983Killinger et al , , 1987Grant, 1987Grant, , 1995Svanberg, 1994;Orr, 2000;Wolf, 2000;Strizik et al , 2008;Platt et al , 2012); and multi-pass absorption spectroscopy, which uses folded-path cell designs such as those of White (1942White ( , 1976 and Herriott et al . (1964) and yields optical pathlengths d eff that are typically hundreds of times the length of the absorption cell itself (Hanst and Hanst, 1994;Schiff et al , 1994;Tittel and Petrov, 2000;Tittel et al ., 2003). However, none of these spectroscopic techniques is actually based on, or enhanced by, genuine optical cavities (other than those intrinsic to lasers themselves, or able to lock or calibrate laser frequencies, or used to build up output laser power for non-linear-optical spectroscopy or wavelength conversion).…”

“…Nevertheless, the diverse range continuously tunable, narrowband mid-infrared lasers that are available to access spectra of fundamental vibrations have tended to be relatively elaborate and remain the subject of much ongoing research (Sorokina and Vodopyanov, 2003;Ebrahim-Zadeh and Sorokina, 2008). The early days of mid-infrared TDLAS (Schiff et al , 1994;Tacke et al , 2000;Tittel and Petrov, 2000) were dependent on lead-salt (e.g., PbS, PbSe and PbTe) diode lasers which need cryogenics (and, often, a mode-selecting monochromator). Within the last 10 years, quantum cascade lasers (QCL) have become commercially available and are now increasingly used for TDLAS applications in the mid-infrared (Curl and Tittel, 2002;Tittel et al , 2003Tittel et al , , 2008Taubman et al , 2004;Kosterev et al , 2008;Mantz et al , 2008;Young et al , 2008;Curl et al , 2010).…”