Resonant optothermoacoustic detection: technique for measuring weak optical absorption by gases and micro-objects

We report a laser spectroscopy technique for detecting optical absorption in gases and micro-objects via linked thermal effects and by using a sharp mechanical resonance in a quartz crystal. The performance of this technique is studied using near-IR diode lasers and two gases, pure CO(2) and C(2)H(2) diluted in nitrogen. A 7.3 × 10(-8) cm(-1)W/(Hz)(1/2) noise equivalent sensitivity to absorption in gases is demonstrated. Based on experimental results, it was estimated that 10(-8) fractional absorption of optical radiation by a micro-object deposited on a thin transparent fiber can be detected.