Silver-halide optical fiber for infrared absorption spectroscopy: Optically pumped intersubband transitions in quantum-well structures

A silver-halide infrared optical fiber is used in a double-beam spectrometer, demonstrating the ability to guide small infrared signals efficiently. We show that a fractional transmission change of less than 1% is easily measured. Use of the fiber may obviate the necessity for the unfriendly optics currently used in spectrometry systems to probe remote sample zones. As a specific example, we were able to guide with high efficiency an infrared signal to and from a sample that was mounted in a cryostat. Using this setup, we measured the photoinduced absorption due to the e1 → e2 intersubband transition in a GaAs-GaAlAs multiple quantum-well structure.