Currently, there are few reliable methods for recording ultrafast single-shot events over long record lengths. Several applications require measurements of 1 picosecond (ps) or better temporal resolution, with record lengths up to 1 nanosecond (ns). The majority of current measurement systems rely on high electronic bandwidth to perform high speed measurements. These approaches generally trade off amplitude resolution for temporal resolution and currently only achieve at best 10ps temporal resolution at the maximum tradeoff.
LLNL researchers have demonstrated a novel single-shot recording technology for transient optical signals in a time regime of picoseconds to nanoseconds for which currently there is a significant instrumentation gap.
The optical switching capability of optical semiconductors can be exploited in a pump-probe style architecture, where an auxiliary pump beam is crossed through the signal to sample a diagonal ‘slice’ of space-time, analogous to a rolling shutter. The slice is then imaged onto an ordinary camera, where the recorded spatial trace is a direct representation of the time content of the signal. The pump samples the signal by optically exciting carriers that modify the refractive index in a conventional semiconductor. The integrating response of the rapidly excited, but persistent carriers is differentiated by probing with and destructively interfering two time staggered signal replicas.
There are several advantages of the SLICER setup:
- The strength of the nonlinear effect can be very high in many semiconductors. Further, the extremely broad range of semiconductor materials allows for measurement of signals across virtually the entire spectrum for which standard optical elements are available.
- Semiconductor materials can typically be made much larger than χ(2) nonlinear optical crystals, resulting in scalability to long records lengths (limited by time of flight).
- There is no stringent angular sensitivity on the pump or signal, allowing for aggressive crossing angles to be used.
SLICER is a one dimensional temporal recorder that exclusively uses the X axis of the wafer to encode information. However, the Y dimension of the wafer is available for use for encoding additional information; many novel devices can be created by reconfiguring what information is encoded in the X and Y axes.
LLNL utilizes the SLICER techniques for observation of the ARC & NIF pulse in time and long record single shot cross correlator.
LLNL has filed a patent application for its SLICER invention that has been reduced to practice. Additional technical information can be made available upon request as appropriate.