General purpose microcomputer-based data acquisition and laser control circuitry for use in one-photon and two-photon laser spectroscopy

Four general purpose circuits are described which facilitate computer control and synchronization of laser firing, analog-to-digital conversion, and digital-to-digital multiplexing. These circuits retain generality by using only the 16 input and output lines of the computer interface without utilization of handshaking or data request lines. Accordingly, these circuits can be used with any 16-bit TTL interface that provides latched output lines. The generality is obtained at the expense of data transfer and control speed and with a loss of interrupt capability. An analog-to-digital converter circuit is described which provides eight computer selected input channels, 12-bit resolution, and a total cycle time for each input reading of ≈60 μs. Each input channel can be independently set to generate a full scale reading for 0.1, 1, or 10 V inputs. A pulse conditioning trigger circuit is described which generates an output pulse of selected delay (50 ns–2 ms), pulse width (30 ns–2.5 ms), and magnitude (up to 10 V) in response to a computer-generated positive going TTL pulse. Applications of the above circuits in controlling and acquiring data from a two-photon laser spectrometer are discussed. A 28-bit to 16-bit digital multiplexer circuit is described which can be used to input data using a 16-bit computer interface from instruments with data words up to and including 28 bits. The EG&G Princeton Applied Research (PAR) model 4202 transient signal averager and the PAR model 1205A optical multichannel analyzer are discussed as examples. Finally, a laser firing circuit specifically designed to provide one-shot triggering of the Chromatix CMX-4 flashlamp-pumped tunable dye laser is described. The unique external triggering requirements of the CMX-4 require a 10-V pulse of 8.34±0.01 ms duration to generate reliable triggering.