We demonstrate a method for measuring optical loss simultaneously at multiple wavelengths with cavity ring-down spectroscopy (CRD). Phase-shift CRD spectroscopy is used to obtain the absorption of a sample from the phase lag of intensity modulated light that is entering and exiting an optical cavity. We performed dual-wavelength detection by using two different laser light sources and frequency-division multiplexing. Each wavelength is modulated at a separate frequency, and a broadband detector records the total signal. This signal is then demodulated by lock-in amplifiers at the corresponding two frequencies allowing us to obtain the phase-shift and therefore the optical loss at several wavelengths simultaneously without the use of a dispersive element. In applying this method to fiber-loop cavity ring-down spectroscopy, we achieve detection at low micromolar concentrations in a 100 nL liquid volume. Measurements at two wavelengths (405 and 810 nm) were performed simultaneously on two dyes each absorbing at mainly one of the wavelengths. The respective concentrations could be quantified independently in pure samples as well as in mixtures. No crosstalk between the two channels was observed, and a minimal detectable absorbance of 0.02 cm(-1) was achieved at 405 nm.
We investigated the effect of Zn doping on the electronic property of magnetite by using optical spectroscopy. The (Zn(x)Fe(1-x))Fe2O4 (ZFFO) (x = 0, 0.2, 0.4, and 0.5) samples were prepared by PLD technique. The XRD measurement revealed that all the samples have an inverse spinel-type of crystalline structure. The M-H curves indicate that the saturation magnetization reduces with the increasing x. From the spectroscopic ellipsometry and infrared spectroscopy, we found that the doping of nonmagnetic Zn2+ ions leads to the dramatic change in the electronic structure of the ZFFO films. We discuss the correlation of our spectra with the electric and magnetic properties of the ZFFO films.
To investigate possible functions of acupuncture, oxygen (O(2)) levels were measured at two different acupuncture points (APs) [Hegu and Laogong] and at the corresponding non-APs (3-5 cm away from the APs) in real time using a high sensitive electrochemical O(2) microsensor. The sensor had a small planar sensing platinum disk (diameter = 25 microm) and therefore was able to monitor the O(2) levels at the localized APs. Significantly higher O(2) levels (p < 0.05) were observed at both APs (n = 5, without exceptions) in comparison with the non-APs. Sufficient sensor sensitivity to distinguish the O(2) level differences between APs and non-APs was achieved. This research provides useful information on possible functions of APs and meridians.
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