Application of a micromachined translatory actuator to an optical FTIR spectrometer

We present a Fourier-transform infrared (FTIR) spectrometer where a micro-opto-electro-mechanical system (MOEMS) replaces the macroscopic mirror drive enabling a miniaturized, robust and low cost system. The MOEMS devices are manufactured in a CMOS compatible process on a silicon on insulator (SOI) substrate. The device consists of a metallized actuator plate with an area of 1.65 mm2 acting as mirror, bearing springs and electrodes for the electrostatic drive. Due to the driving principle based on in-plane electrode combs, 200m translatory displacement can be achieved with comparatively low voltages (<40 V) at an ambient pressure below 500 Pa. The actuator operates at a resonant frequency of 5 kHz. Consequently this yields a maximum spectral resolution of 25 cm-11 and an acquisition time of 200 s per spectrum. Based on a Michelson setup the infrared optical bench of the presented FTIR system is designed to account for the mirror aperture and the desired spectral band width of 2 m to 5m. The integrated signal processing electronics has to cope with a bandwidth of 8 MHz as a result of the mirror motion. A digital signal processor manages system control and data processing. Furthermore, high-level analysis algorithms can be applied without the need of an external PC. The high acquisition rate and integration level of the system makes it appropriate for applications like process control and surveillance of fast reactions. First results of transmission and absorbance measurements are shown.