Discrete frequency infrared microspectroscopy and imaging with a tunable quantum cascade laser

Area of Science:

• Spectroscopy
• Microscopy
• Infrared Imaging

Background:

• Fourier-transform infrared (FT-IR) imaging is a standard technique but is often inefficient, requiring extensive spectral data.
• Emerging discrete frequency infrared (DF-IR) methods utilize targeted spectral measurements for faster analysis.
• Advancements in tunable, narrow-bandwidth laser sources are crucial for DF-IR method development.

Purpose of the Study:

• To introduce and evaluate a discrete frequency infrared (DF-IR) imaging microscope.
• To compare the performance of two DF-IR configurations against a commercial FT-IR imaging instrument.
• To investigate the impact of laser coherence properties on imaging quality.

Main Methods:

• Development of a DF-IR imaging microscope utilizing an external cavity quantum cascade laser (QCL).
• Implementation and testing of two detector configurations: uncooled bolometer and liquid nitrogen-cooled mercury cadmium telluride (MCT).
• Comparative performance analysis with a commercial FT-IR imaging system and examination of beam coherence effects.

Main Results:

• The DF-IR microscope demonstrated comparable performance to FT-IR imaging.
• The use of a tunable laser source proved advantageous for high-quality point mapping with small apertures.
• Coherent properties of the laser beam were analyzed and simulated for their impact on imaging.

Conclusions:

• The developed DF-IR imaging microscope shows promise for efficient infrared microscopy.
• Tunable laser sources offer significant advantages over broadband sources in specific IR imaging applications.
• DF-IR imaging presents a viable alternative for applications requiring rapid spectral analysis.