Terahertz quartz enhanced photo-acoustic sensor

A quartz enhanced photo-acoustic sensor employing a single-mode quantum cascade laser emitting at 3.93 Terahertz (THz) is reported. A custom tuning fork with a 1 mm spatial separation between the prongs allows the focusing of the THz laser beam between them, while preventing the prongs illumination. A methanol transition with line-strength of 4.28 x 10(-21) cm has been selected as target spectroscopic line. At a laser optical power of similar to 40 mu W, we reach a sensitivity of 7 parts per million in 4s integration time, corresponding to a 1 sigma normalized noise-equivalent absorption of 2 x 10(-10) cm(-1) W/Hz(1/2). (C) 2013 AIP Publishing LLC.