Development of vacuum‐ultraviolet circular dichroism measurement system using a polarizing undulator

Abstract

We have developed an improved circular dichroism (CD) and linear dichroism (LD) simultaneous measurement system for the vacuum ultraviolet (VUV) region by polarization modulation techniques using a four-period Onuki-type crossed undulator as a polarized light source. The system has been constructed at the VUV beamline BL-5 in the electron storage ring TERAS, at AIST. Our improvements, in particular the adoption of an optical chopper as the detection method of incident light, have resulted in a flat baseline and a consequent simplification of the Mueller matrix calculation for our optical system. Based on the Mueller matrix calculation, we have successfully measured real VUV-CD and LD spectra of leucine films for wavelengths down to 160 nm with absolute optical constants. The obtained spectra show good consistency with spectra measured by conventional methods.

Compact optical cell system for vacuum ultraviolet absorption and circular dichroism spectroscopy and its application to aqueous solution sample

“…These spectra of the ACS aqueous solution were measured at the TERAS BL-5 [10][11][12][13] of the National Institute of Advanced Industrial Science and Technology and calibrated using the calibration method recently developed by us. 20 Powders of S-and R-ACS were purchased from Kanto Kagaku and Sigma Aldrich Japan, respectively, and dissolved in distilled water.…”

“…If the windows have linear anisotropy, the recorded CD and LD spectra may be disturbed because of their anisotropy, and the description of the recorded signal based on the Mueller matrix calculation may be too complicated to extract the true CD and/or LD signals. 10 Therefore, superfluous optics such as windows should be not used if possible, because high vacuum is required to prevent the change in the polarization of incident light in this system and the optical cell.…”

“…These facilities have adopted PEM for the modulation of circular polarization. Recently, we have developed a unique VUV-CD measurement system [10][11][12][13] using a polarizing undulator instead of PEMs as a polarized light source. The polarizing undulator can irradiate bright polarized light.…”

“…It is therefore the most suitable polarized light source and has been utilized to obtain VUV-CD and linear dichroism (LD) spectra. 10,11 Our VUV-CD measurement system 10-13 using the polarizing undulator required the evacuation of the whole optical path including the optical cell in high vacuum. This is because it is difficult to use this system with transparenttype optics such as windows, owing to its polarization characteristic as well as its absorbance.…”

“…If the window has linear anisotropy, the observed CD signal consists of not only a real CD signal but also a signal originating from the linear anisotropy. 16 To measure the y dependence, the cell is rotated around the z-axis using a rotatable axis stage (10), and its center is adjusted to the light spot using a dual-axis x-y stage (9), as shown in Figure 1b. The definitions of the x, y, and z directions and the rotational angle y are illustrated in Figure 1b.…”