MEMS scanning mirror used as an laser external modulator for photoacoustic spectroscopy

We present a novel MEMS application aimed at laser based gas sensing. A low-cost MEMS based external intensity modulator for a laser diode source has been realised and applied to photoacoustic spectroscopy. By using a MEMS based modulator, pure intensity modulation of the laser emission is achieved without the accompanying wavelength modulation which occurs with diode current modulation. This reduces measurement error. We describe the use of the optical MEMS modulator/photoacoustic technique to recover the profile of the 1535.4nm absorption line of acetylene at 100pm concentration in the photoacoustic cell. Based on initial results, we predict a sensitivity of ~1ppm with this system.