Infrared circular dichroism measurement apparatus

An infrared circular dichroism measurement apparatus comprising:

• a laser light source capable of sweeping a wavenumber of a laser light in an infrared wavenumber range containing at least one absorption peak of a sample;
• a sample chamber where the sample is disposed;
• a polarization modulator that modulates a polarization state of the laser light either before or after the laser light, which is swept in a specific wavenumber, transmits the sample;
• a detector that detects a variation in intensity of the laser light which has transmitted the sample and of which its polarization state is modulated;
• and
• a signal processing device, including at least a processor and a memory, that is configured to:
• extract an alternating-current component (AC) that synchronizes with a modulation frequency and a direct-current component (DC) from a detected signal of the detector;
• calculate a value of infrared circular dichroism of the sample based on a ratio (AC/DC) of the AC and the DC;
• store an absorption peak wavenumber of water or water vapor;
• determine whether the swept wavenumber of the laser light matches with the absorption peak wavenumber of water or water vapor;
• and
• execute a processing of avoiding influence of the absorption peak when the wavenumbers match, wherein the signal processing device is further configured to calculate the infrared circular dichroism value in the absorption peak wavenumber of water or water vapor based on the infrared circular dichroism value by the laser light of the swept wavenumber before and after the absorption peak wavenumber of water or water vapor.