Abstract
A pulsed, distributed feedback (DFB) quantum cascade laser centered at was used in combination with a wavelength modulation spectroscopic technique for the detection of acrylonitrile. The laser was excited with short current pulses (), and the pulse amplitude was modulated with a linear subthreshold current ramp at resulting in a frequency scan. This allowed the measurement of spectroscopic features of acrylonitrile with absorption line widths of . A demodulation approach followed by numerical filtering was utilized to improve the signal-to-noise ratio. We then superimposed a sine wave current modulation on top of the current ramp. The resulting high frequency temperature modulation of the DFB structure results in wavelength modulation. A minimum detectable absorbance of , corresponding to the sub levels of acrylonitrile, was achieved with less than a minute averaging time.
© 2011 Optical Society of America
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