Femtosecond laser pulse diagnostics

Special instrumentation is required to measure and analyze laser pulses below one nanosecond because of the limitations of standard instrumentation used to measure real-time signals. We have designed and developed an instrument with unique features to measure the pulsewidth of single laser pulses below one nanosecond using the standard autocorrelation technique. A single laser pulse is divided into two equal pulses by a 50/50 beamsplitter and recombined in space and in time inside a wafer of KDP crystal which generates a second harmonic of each fundamental pulse and a second harmonic of the combined pulses. These three pulses are then focused on a charge-coupled device (CCD) camera and analyzed by a laser beam analyzer to yield information on the FWHM (full-width-half-maximum) time of the original pulse. By using a CCD camera the full two-dimensional image can be recorded to insure that the correct horizontal profile is analyzed within the vertical profile. The delay for overlapping the beams in time is obtained by translating the beamsplitter while the positioning is obtained by rotating the beamsplitter. The design and results are discussed.