Quantum Cascade Laser-Based Vibrational Circular Dichroism Augmented by a Balanced Detection Scheme

Area of Science:

• Spectroscopy
• Chiroptical techniques
• Molecular spectroscopy

Background:

• Vibrational Circular Dichroism (VCD) is crucial for determining molecular absolute configuration without chiral reagents.
• VCD signals are typically weak, requiring long measurement times for adequate signal-to-noise ratios (SNRs).
• Existing Fourier transform infrared (FT-IR) instruments have limitations in VCD measurement speed.

Purpose of the Study:

• To present an improved setup for enhanced VCD measurements.
• To reduce measurement times while maintaining high signal quality.
• To enable faster analysis of molecular chirality.

Main Methods:

• Utilized an external cavity quantum cascade laser (EC-QCL) as a high-power light source.
• Implemented a balanced detection module with a custom optical path for VCD.
• Employed a two-detector setup for enhanced laser noise stabilization.

Main Results:

• Achieved competitive noise levels in VCD spectra within 5 minutes.
• Demonstrated noise level improvements up to a factor of 4 compared to single-detector EC-QCL-VCD.
• Reduced measurement times by at least a factor of 6 compared to commercial FT-IR instruments, with comparable noise levels.

Conclusions:

• The improved EC-QCL-VCD setup significantly accelerates VCD measurements.
• The system is applicable for both qualitative and quantitative VCD analyses.
• The high temporal resolution opens possibilities for monitoring optically active processes in real-time.