Spectroscopic application of long-wavelength (< 2 μm) VCSEL diode lasers

Vertical-cavity surface-emitting lasers (VCSELs) are used for rapid in-situ direct molecular spectroscopy. The method of tunable diode laser spectroscopy (TDLS) is applied to measure oxygen at 760 nm, ammonia at 1540,nm, methane at 1680 nm, and hydrochloric acid plus water at. 1810 nm. Atmospheric pressure broadened and subatmospheric high resolution spectra are recorded. The principle of a spectrometer with long term stability is presented. The wavelength modulation properties of the VCSELs with temperature and injection current are investigated. While the temperature tuning coefficient is essentially the same as for conventional (edge emitting) diode lasers in the near infrared spectral region (DFB lasers), VCSELs can be wavelength tuned by the injection current much further. Also, VCSELs can be wavelength tuned much faster than edge emitters. Repetition rates up to 5 MHz are demonstrated. New fields of applications With respect,to the wide mode hopping free single frequency tuning range (measurements at high pressures, of multiple species, and of temperature distributions) and to the rapid wavelength tunability (investigation of extremely transient processes) are discussed. Particularities of the VCSELs of special interest for the spectroscopist (low threshold and operating current as a benefit for-battery powered portable devices, potential for on wafer testability) are addressed. The long wavelength InP based VCSELs with lambda > 1 mum have become available just recently, yet it is expected that they will quickly find their way into molecular spectroscopy and extend the field of use for diode laser based sensors and systems to high pressure and difficult environments.