An ultra-fast photodiode for picosecond optical, UV, and x-ray detection

Fusion and high energy density physics facilities perform ultra-fast timing experiments that require good quantum efficiency in deep ultra violet regimes. As an example, beam timing measurements at free electron laser facilities monitor timing for electron bunch pulses with 100 kHz repetition rates in laser-driven shock, plasma, and optical/UV pump-probe experiments. These measurements require detector rise-fall times to be below 50 ps to monitor coarse timing. Device size is another important factor, particularly in the crowded and complex target chambers of fusion facilities. The need for robust, condensed packaging, and picosecond time resolution extends to fields of laser characterization, synchrotrons, and high-speed communication. There is not currently a fast photodiode available on the market with a UV/x-ray response time < 50 ps. A photodiode based off of a metal semiconductor metal technology will be fabricated, tuned and tested to produce < 50 ps response times with high QE for ultra violet and x-ray wavelengths. To complement this technology, commercially available readout electronics will be tested and vetted for distribution with the devices. During Phase I, knowledge transfer for diode photo-lithographic fabrication was completed, and early prototype photodiodes indicated that the proposed direction for fabrication was commercially viable. Phase II continued prototyping the fast detectors, resulting in the build and test of approximately ten devices with a rise time below 50 ps, the target timing performance required to replace a solution that is no longer commercially available. Additional work went in to identifying and testing a commercial fast digitizer that can be paired with the detector for applications where a fast oscilloscope is not required or cost prohibitive. The main objective of Phase IIB will be to develop and test a detector capable of resolving a < 50 ps pulse shape while maintaining the fast rise time of prototypes developed in Phase II. P-I-N structures and new substrate materials for the detectors will be prototyped and integrated into the new and improved device. This effort will also include determining the best commercially available digitizer to pair with the devices and writing interfacing software accordingly. A commercially supported fast photodiode with sub-50 ps resolution will enable scientists to conduct otherwise impossible timing measurements in pulse time monitoring and pump-probe experiments. Free electron laser facilities and pulsed soft x-ray source researchers will be able to measure pulse to pulse variations. Larger facilities observing dozens of ultra-violet and soft x-ray pulses simultaneously can take advantage of the integrated electronics, removing the need to allocate expensive oscilloscopes to a single application.