Accurate and quick calibration method for polarization-modulation spectroscopy using an ac-modulated polarizing...

Area of Science:

• Spectroscopy
• Optical Physics
• Materials Science

Background:

• Accurate calibration is crucial for polarization modulation spectroscopy, especially in the vacuum ultraviolet (VUV) region.
• Established standard samples for VUV circular dichroism (CD) and linear dichroism (LD) calibration are lacking.
• Existing calibration methods can be time-consuming and may not fully account for experimental variations.

Purpose of the Study:

• To propose and validate an accurate calibration method for VUV CD and LD spectroscopy.
• To utilize an ac-modulated polarizing undulator and a multireflection polarimeter for calibration.
• To establish a reliable calibration procedure in the absence of standard samples in the VUV region.

Main Methods:

• An undulator-modulation spectroscopic method was employed using a multireflection polarimeter.
• The polarimeter was treated as a standard sample for calibration.
• Calibration factors were determined for CD and LD spectra across a wide wavelength range (120-230 nm).

Main Results:

• The proposed calibration method was successfully applied to VUV CD and LD spectra at the TERAS storage ring (BL-5B).
• Calibrated spectra showed good agreement with standard spectra above 170 nm (mean differences of ~7% for CD, ~4% for LD).
• Experimental time was significantly reduced from ~1 hour to <10 minutes, allowing observation of storage-ring current dependence.

Conclusions:

• The ac-modulated polarizing undulator method provides accurate calibration for VUV CD and LD spectroscopy.
• This method offers a substantial reduction in experimental time and enhances spectral reliability.
• The technique is applicable to VUV-CD spectra obtained with conventional modulators, facilitating precise protein secondary structure analysis.