Recent progress in vacuum-ultraviolet polarization modulation spectroscopy using polarizing undulator at the TERAS BL5 beamline

Abstract

Polarization modulation spectroscopy using an Onuki-type undulator is a useful technique for circular dichroism study in the vacuum-ultraviolet region. We have been developing the vacuum-ultraviolet circular dichroism (vuv-CD) spectroscopy in TERAS BL5 beamline at AIST. This paper describes recent improvements in our instrumentation and methods of analysis to achieve precise and absolute measurements. The CD signal is usually accompanied by experimental artifacts, and elimination of all possible artifacts is the key issue for making reliable measurements. After improving beamline optical system, light flux monitor, and undulator operation method, the base line shift of the CD spectrum is suppressed less than 3x10(-4). Sample manipulation and data processing procedures are also described and absolute CD spectrum can be obtained even for linear anisotropic sample. These progresses lead to more quantitative comparison of experimental with calculation on vuv-CD spectrum.

First observation of natural circular dichroism spectra in the extreme ultraviolet region using a polarizing undulator-based optical system and its polarization characteristics

“…The intensity of stray light is estimated to be less than 1% in the EUV region by measuring the light intensity through a Pyrex glass window. Details of the beamline have been given in our previous report (Yagi-Watanabe et al, 2007).…”

“…In general, signals of natural CD of optical absorption are relatively weak ($ 0.01-1% of absorption intensity); hence, AC modulation of circular polarization is essential. Natural CD spectra at wavelengths down to 130 nm have already been obtained with a sensitivity of approximately 0.01% by using our CD system (Kaneko et al, 2009;Yagi-Watanabe et al, 2007).…”

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.…”

“…21 Details of VUV-CD measurements at the TERAS BL-5 and the calibration method have been reported elsewhere. [10][11][12][13] The calibrated CD spectrophotometer (J720WI, JASCO) was also used to obtain the standard CD spectra of ACS aqueous solutions. 22 The optical path length was calculated by following the Lambert-Beer law using values for the observed optical density, concentration (240 mM), and molar absorption coefficient.…”

“…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.…”