Tandem demodulation lock-in amplifier based on digital signal processor for dual-modulated spectroscopy

Area of Science:

• Spectroscopy
• Materials Science
• Electrical Engineering

Background:

• Dual-modulated spectroscopy is a powerful technique for material characterization.
• Traditional methods using cascaded lock-in amplifiers (LIAs) can introduce errors and limitations.
• Existing commercial LIAs have constraints on time constants and frequency ratios.

Purpose of the Study:

• To develop and implement a novel tandem lock-in amplifier (LIA) for dual-modulated spectroscopy.
• To present a new tandem demodulation algorithm and its theoretical analysis.
• To demonstrate the advantages of the tandem LIA over traditional methods.

Main Methods:

• Development of a digital signal processor-based tandem LIA.
• Implementation of a novel tandem demodulation algorithm.
• Application in photoreflectance (PR) measurements of GaAs and GaSb materials.

Main Results:

• The tandem LIA eliminates redundant analog-to-digital and digital-to-analog conversion errors.
• It removes the time constant limitation found in commercial LIAs.
• Successful PR spectra measurements of GaAs and GaSb were achieved with good lineshapes and signal-to-noise ratios.

Conclusions:

• The developed tandem LIA offers improved accuracy and reduced experimental complexity for dual-modulated spectroscopy.
• It lowers requirements for frequency ratios in dual-modulated spectroscopy.
• The tandem LIA proves efficient and advantageous for photoreflectance measurements compared to traditional two-LIA setups.