Investigation and characterization of high-efficient NIR-scanning gratings used in NIR-micro-spectrometer

Spectroscopy in the infrared region is today an important application to measure, control and investigate liquids or gases in industrial, medical or environmental applications. We have developed a small, transportable NIR-spectrometer with a size of only 120 x 80 X 80 mm(3), and a MOEMS-scanning-grating chip as main element. The scanning-grating chip is resonantly driven by a pulsed voltage of only 36V, has a mirror aperture of 3 x 3 mm(2) and reaches maximum deflection angles of +/- 11 degrees. The NIR-micro-spectrometer works currently in a spectral range of 1200 - 1900 nm with a resolution of less than 10 nm using only one single InGaAs-diode as detector. Additionally, scanning grating chips have been already developed for spectral ranges of 900 - 1800 nm and 1250 - 2500 nm. One entire spectral measurement is done within 6 milliseconds, calculated by a digital signal processor, which is included in the spectrometer. Results can be either displayed by special Computer software or directly by a graphical user interface. In this paper, we will. focus on the control of the grating fabrication process, which can be done by microscopy, using new control structures. A time-consuming control with SEM (Scanning electron microscope) is no longer needed. Furthermore the characterization of the fabrication process and its consequence on the spectrometer properties will be discussed, as well as the characterization of the scanning grating chip itself (frequency, movement, static deformation, spectral efficiency...). Characteristic measurement results of an argon calibration lamp, which shows the performance of the NIR-micro-spectrometer, will be presented as well.