Passive imaging with a highly-sensitive infrared phototransistor

A scanning confocal long-wavelength infrared (LWIR) microscope has been developed by using a highly-sensitive, novel LWIR detector (charge-sensitive infrared phototransistor) for wavelengths -14.7 mum. Samples and Ge objective lens are placed at room temperature, while other optics including a confocal pinhole, Ge relay lenses, and the detector are cooled down to 4.2 K. Passive LWIR imaging has been achieved with a spatial resolution of 25 mum, which was kept unchanged when the sample surface was covered by a GaAs or Si plate. This work indicates the usefulness of the CSIP for application in passive LWIR microscopy.