Handheld infrared spectrometer

A method of identifying a material composition of a sample, comprising:

• (a) providing a handheld device for light reflectance measurements, the device comprising:
• a housing including a window through a housing wall, the window being disposed on the housing in an exterior position such that the window may be placed against a surface of the sample;
• a lens mounted in the housing to concentrate light onto an area on the surface of the sample;
• a reflectance detector adjacent the area;
• a lamp aligned with the lens to provide the light on the area of the surface of the sample;
• and
• optical analysis means for determining the material composition, comprising
• an acousto-optic tunable filter disposed between the lamp and the lens, and
• electronic means for driving the filter at a swept frequency, comparing a reflectance spectrum of the sample with a reference spectrum, determining the material composition, and outputting an analysis of the material composition;
• wherein
• the lamp, the lens, the tunable filter, and the window are aligned on a common optical axis,
• the detector includes a hole aligned on the common optical axis, and
• the detector includes at least one detector element offset from the optical axis;
• and
• (b) placing the window against the sample.