Charge-Line Dual-FET High-Repetition-Rate Pulsed Laser Driver

Most modern pulsed laser systems require versatile laser diode drivers. A state-of-the-art pulsed laser driver should provide precise peak power regulation, high repetition rate, and pulse duration control. A new, charge line dual-FET transistor circuit structure was developed to provide all these features. The pulsed modulation current is adjustable up to Imax = 1.2 A, with the laser diode forward voltage acceptable up to UF max = 20 V. The maximum repetition rate is limited by a charge line circuit to frep max = 20 MHz. Compared to the conventional single transistor drivers, the solution proposed in this paper allows a precise, high resolution width regulation to be obtained, whereas a low pulse jitter is ensured. In the solution, two separate, out-of-phase signals are used to trigger the individual Field Effect Transistors (FET). The resultant pulsed modulation current full-width-at-half-maxima (FWHM) is regulated from ~200 ps up to 2 ns. All control and timing signals are generated with a popular Field-Programmable Gate Array (FPGA) digital circuitry. The use of standard FPGA devices ensures the low cost and high reliability of the circuit, which are not available in laser drivers consisting of sophisticated analogue adjustable delay circuits.