Application of power stabilized laser to the uncooled infrared imaging system

A new new kind of IR imaging system which is based on MEMS microcantilever has come out in recent years. The infrared radiation detection and the subsequent reconstruction of an image are based on the deflection of individual microcantilever pixels. This detection is applied in an optical way, which means there is no electrical contact to each individual pixel. This approach has drawn considerable attention due to the advantages of low cost, light weight, low power consumption, high reliability and no back-ground electrothermal noise. Firstly the incoming IR light is blocked and an image of the microcantilever array is captured by a camera as a background image before an optical readout process. Then the IR light is let in and the difference between the background image and the current image captured is calculated and exported as an IR video signal. This process has a critical demand on light power stability. A CCD of 12 bit resolution is used to achieve a high signal to noise ratio. Its resolution is 4096 which means it can detect a light power changing of 1/4096 or 0.02% theoretically. The instability of common lasers is a few percent and the long time instability of LED light sources can be about 1%. These instabilities are all larger than 1/4096. The power variation can be detected by the CCD if these lasers or LEDs are used as the light source in the system. This power variation will affect the signal to noise ratio of an output IR signal. We have done some experiments in this paper. The laser power stabilizer consists of an electro-optical modulator and an optical feedback system. The peak-to-peak instability of the laser output power reaches within 0.1% in a few minutes. The stabilized laser beam is applied to the optical readout process. The experiment shows that the output IR image is much more stable than before. The drift of light power is almost eliminated. The NETD of the whole system reaches about 2 K.