Infrared spectroscopy based on broadly tunable quantum cascade lasers and polycrystalline diamond waveguides

Area of Science:

• Spectroscopy
• Laser Technology
• Materials Science

Background:

• Fourier transform infrared (FTIR) spectroscopy traditionally uses thermal emitters and interferometers.
• Diamond's robustness and chemical resistance make it ideal for attenuated total reflection (ATR) sensing.
• Material absorption in diamond can limit optical path length in ATR setups.

Purpose of the Study:

• To present a novel spectroscopic sensing design using tunable quantum cascade lasers (tQCL) and polycrystalline diamond (PCD) ATR elements.
• To overcome the limitations of optical path length in diamond ATR sensors.
• To demonstrate the potential for sensitive mid-infrared (MIR) spectroscopic analysis of complex matrices.

Main Methods:

• Integration of bright, broadly tunable quantum cascade lasers (tQCL) with a multi-reflection polycrystalline diamond (PCD) ATR element.
• Achieving an extended optical beam path length of approximately 5 cm within the diamond ATR element.
• Utilizing MIR spectroscopy for vibrational analysis.

Main Results:

• Enabled sensitive spectroscopic measurements in the mid-infrared (MIR) range.
• Demonstrated non-invasive glucose monitoring in human saliva with high sensitivity and selectivity.
• Validated the effectiveness of the tQCL-PCD ATR system for analyzing complex biological samples.

Conclusions:

• The combination of tQCLs and PCD ATR elements offers an efficient laser-based vibrational spectroscopy alternative.
• This robust sensing interface facilitates direct analysis of molecular constituents in challenging biomedical and biochemical matrices.
• The proposed analytical concept holds significant promise for non-invasive diagnostics and chemical analysis.