Versatile precision source ratioing system for fast kinetic spectroscopy

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Abstract
A system is described for the reduction of source intensity fluctuation errors in rapid kinetic spectroscopy. The system provides ratioing of the observed signal by a reference of source intensity. This operation is performed by true division in real time with an accuracy of ±0.15% over a ten‐fold source intensity range and with a rise time of 11 μsec. Silicon photodiodes, operational amplifiers, and an electronic analog divider are used. The frequency response was evaluated with a modulated LED source, showing ≳ 100‐fold rejection of common mode sinusoidal modulation for frequencies dc through 10 kHz. Broad band noise reduction of 100‐fold was achieved for a He–Cd laser, running with ∼20% peak‐to‐peak noise. While designed initially for stopped flow spectroscopy, these characteristics are suitable for a wide range of rapid kinetic techniques with microsecond time response (e.g., temperature jump, light scattering, Raman, flash photolysis, and fluorescence) using both laser and arc sources.

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