Isa-diode laser spectrometer



A Compact Ruggedized Tunable Diode Laser Spectrometer for Oxygen Sensing
Mikko Laakso Product Line Manager Vaisala Oyj PO Box 26 FI-00421 Helsinki FINLAND Marko Jalonen R&D EngineerVaisala Oyj PO Box 26 FI-00421 Helsinki FINLAND Samuli Laukkanen R&D Engineer Vaisala Oyj PO Box 26 FI-00421 Helsinki FINLAND

KEYWORDS
TDL, spectrometer, oxygen sensor, oxygen analyser, oxygentransmitter

ABSTRACT
Key results from the development work towards a compact ruggedized Tunable Diode Laser Absorption Spectrometer (TDLAS) and sensor for industrial gas analysis are presented. Theoptomechanical design of the sensor minimizes the unwanted interference and ethalon effects as well as optical feedback to the diode laser light source. All sensor parts are of a compact design that makesit possible to fit the optical path inside an insertion probe of a reasonable size. Main principles, advantages and limitations of the TDLAS technique will be briefly reviewed. Results from opticalmodelling and simulations of the sensor structure will be presented. Highlights and main results from the development work towards a measurement algorithm and electronics appropriate for a compact fieldinstrument will be described. In the experimental part, the basic performance characteristics of the instrument will be shown with oxygen as the test gas. Furthermore the performance of the sensorand instrument for oxygen measurements in widely varying environmental conditions will be presented. Finally, the potential application areas for the instrument will be discussed.

INTRODUCTION
Theuse of optical absorption spectroscopy for gas detection has a long history. The use of tunable diode lasers as light sources has long been considered promising in optical absorption spectroscopybecause of the many attractive properties of these lasers, such as small size and low power consumption. The emission wavelength of such a laser can be tuned by either direct heating or cooling of the...