Single-Shot Optical Recorder with Picosecond Resolution and Nanosecond Record Length

John Heebner (15-ERD-055)

Project Description

There have been numerous research and development efforts to build advanced optical laser-based technologies capable of achieving sub-picosecond resolution with recording lengths on the nanosecond scale to record the dynamics of materials under extreme conditions of temperature and pressure. However, these complex systems have not found widespread use because of challenges associated with their manufacture, portability, or spectral versatility. Our goal is to develop and demonstrate an advanced recording capability that bridges the picosecond-to-nanosecond time gap in a simple, portable geometry that is spectrally versatile. Ultrafast, single-shot recording technologies are an essential capability for many experimental programs at Livermore. Unfortunately, the temporal resolution of these technologies has been outpaced by the timescales associated with experimental signatures. We will develop a recording technique using a waveguide chip, a pump laser to gate the incoming signal as a function of space, and an ordinary camera to image the output of the waveguide. This arrangement effectively maps the temporal content of the signal across a lateral dimension of the camera for recording. If successful, the diagnostic we develop (called Slanted Light Interrogation for Cross-Correlated Encoded Recording or SLICER) will bridge a time gap that has long existed between commercially available oscilloscopes possessing long record lengths and ultrafast optical techniques with sub-picosecond resolution. We expect to deliver a working demonstration of a single-shot recording technique with 1-ps resolution across 1 ns of record length with wide spectral versatility. The diagnostic will be portable and tested with direct measurement of a Livermore Advanced Radiographic Capability pulse on a single shot for the first time.

Mission Relevance

The development of SLICER, which is being designed to directly measure a laser pulse for a single shot on the Advanced Radiographic Capability, is a project that aligns with Livermore's core competency in lasers and optical science and technology in the area of ultrafast diagnostics. Additionally, this capability supports Livermore's core competency in high-energy-density science, which relies on advanced fusion-class lasers to further its research. This technology will also be of interest to government contractors and commercial suppliers of high-speed instrumentation. Finally, the work will generate peer-reviewed publications as well as new intellectual property.

FY16 Accomplishments and Results

In FY16 we (1) successfully demonstrated a working prototype of the chip-scale recorder based on dark-field imaging that gave sub-picosecond resolution and a record length consistent with time of flight; (2) determined, however, that the limitations of the current gallium arsenide two-dimensional waveguide fabrication resulted in a large scattering background, which greatly reduced the fidelity of the measured signal; (3) devised a new dark-field method based on birefringent cancellation that was successfully demonstrated with bulk semiconductors; and (4) demonstrated that the new dark-field method possessed several advantages over the previously proposed waveguide design, including greatly enhanced limit of temporal resolution, reduced alignment sensitivity, access to more than one row of pixels on the camera to capture more data, and the ability to scale the experiment to longer records (see figure).

$Semiconductors, such as silicon or gallium arsenide, are of interest for ultrafast camera shutters because their refractive indices are strongly and rapidly changed when optically pumped, so we incorporated them into the slanted light interrogation for cross-correlated encoded recording (slicer) diagnostic. unfortunately, the refractive index change is sustained for several nanoseconds, resulting in an integrating response (a). by taking the optical derivative of this response, an ultrafast optical shutter$

Semiconductors, such as silicon or gallium arsenide, are of interest for ultrafast camera shutters because their refractive indices are strongly and rapidly changed when optically pumped, so we incorporated them into the Slanted Light Interrogation for Cross-Correlated Encoded Recording (SLICER) diagnostic. Unfortunately, the refractive index change is sustained for several nanoseconds, resulting in an integrating response (a). By taking the optical derivative of this response, an ultrafast optical shutter is created (b). Recorded data (c) of a single-shot SLICER trace (black) of a double-pulse pattern demonstrating sub-picosecond resolution and record length of 50 ps. For comparison, we overlay a single-shot recording using a state-of-the-art 45 GHz photodiode and oscilloscope (blue), as well as the trace from a scanning autocorrelator (red).