Photothermal deflection spectroscopy of an aqueous sample in a narrow bore quartz capillary
- Energy and Environmental Technologies Division, Lawrence Berkeley National Laboratory, M/S 70-193A, Berkeley, California 94720 (United States)
- Forensic Science Center, P.O. Box 808 L-178, Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
An apparatus to perform photothermal deflection spectroscopy on liquid samples within a cylindrical capillary is described. A tunable dye laser, modulated by an optical chopper, serves as an excitation source. The resolution of a spectral absorption peak near 575 nm, of a 1{times}10{sup {minus}3}thinspM Nd{sup 3+} aqueous solution, demonstrates the effectiveness of the system. The sample is contained within a 75 {mu}m internal diameter quartz capillary, typical of those used for capillary electrophoresis. Across the middle of the probed section of the capillary, the magnitude of the resolved peak is 5.2{times}10{sup {minus}5} absorbance units. A helium{endash}neon laser, focused to a 1/e{sup 2} waist diameter of 40 {mu}m, provides an optical probe beam across the center of the sample, overlapping the excitation beam at an angle of 3{degree}. Maximum signal-to-noise ratio is achieved with the apparatus when the excitation beam is modulated at a frequency near 205 Hz. The deflection responsivity of the probe beam at this frequency is 650 nrad per {mu}W of absorbed excitation radiation, with an internal noise level in the system of 0.6thinspnradthinspHz{sup {minus}1/2}. The shot noise from probe beam radiation upon the photodiodes in the position sensitive detector exceeds noise from other sources.
- OSTI ID:
- 634252
- Journal Information:
- Review of Scientific Instruments, Vol. 69, Issue 6; Other Information: PBD: Jun 1998
- Country of Publication:
- United States
- Language:
- English
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