A simple and fast photometric signal processing unit has been constructed using some of the commonly available linear and digital integrated circuits. A common mode rejection ratio of 75 dB, based on the subtraction of the output and reference signal, and a rise time of 0.2 μs have been achieved with this instrument.

Different configurations of an analog gated base‐line restorer circuit are discussed. An elimination of a ‘‘droop’’ rate is achieved by replacing the analog memory by a digital one. A design employing a digital feedback loop is described.

Fast and simple photometric signal processing unit.

Gated base‐line restorer without ‘‘droop’’

A new instrument has been designed for the recording of chemical relaxation phenomena induced by a temperature jump, using changes in the nonpolarized and polarized emission of fluorescent molecules. The relative features of techniques for the measurements of light absorption and light emission are discussed specifically in regard to the signal‐to‐noise ratios of the measured signals and to problems related to the detection of polarized emission. Examples are given to demonstrate both the performance of the instrument as well as the usefulness of fluorescence measurements in chemical relaxation experiments.

A temperature‐jump apparatus for fluorescence measurements

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.

Fast and simple photometric signal processing unit.

Citations

Gated base‐line restorer without ‘‘droop’’

References

A temperature‐jump apparatus for fluorescence measurements

Versatile precision source ratioing system for fast kinetic spectroscopy

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