The performance and the characteristics of an interferometric double-mirror spectrometer with uncollimated light are studied by measuring spectra of different radiation sources. The stationary interferometer is fabricated without a beam splitter or moving components. The measured interferogram visibilities, which are limited by the size of the source aperture, agree with the theoretical predictions for a slit and a circular source aperture. By background subtraction the effect of detection nonuniformity can be radically reduced to increase the dynamics and the resolving power of the spectrometer. We used a mercury pencil lamp for measurement and found that the dynamic range was ~ 80 dBm. When isolated spectral lines are measured, the resolving power can be improved by squeezing more than half of a spatial interference cycle onto one pixel. The maximum resolving power reached in measuring the spectra of a diode laser was 1600. The instrument is applicable to a wide range of measurements, such as the recording of temporally variant, wideband radiation sources and the monitoring of laser wavelength.
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