Single Photon Detector and 3D Imaging

Remote Ultra-Low Light Imaging (RULLI) is a sensor system technology enabling breakthroughs in many application arenas. The core of the technology is a single-photon detection system. The RULLI sensor system measures, accurately and simultaneously, the position and absolute time of arrival for each detected photon. This opens up many new possibilities for the exploitation of this literally three dimensional data. This Los Alamos technology project is funded by the US Department of Energy.

Technology

The RULLI technology consists of three primary components: the MicroChannel Plate/Crossed Delay Line (MCP/CDL) detector, the Pulse Absolute Timing (PAT) electronics, and associated photon event construction and data processing techniques.

Sensor: The MCP/CDL detector is a hermetically sealed vacuum tube which contains the light sensing material (photocathode) on the backside of the transparent window, a Z-stack of three microchannel plates, and a crossed delay line readout. It offers a high signal read-out rate and good spatial resolution. To date, we have implemented a series of detectors each using a 40 mm diameter MCP (which defines the detector's active area) and an S-20 photocathode which is sensitive in the visible regime.

Electronics: The PAT electronics is a fast and accurate timing technology with heritage from the nuclear test program at Los Alamos. The PAT system measures the absolute arrival time of individual electrical pulses with an accuracy better than 20 picoseconds.

Data Exploitation: The combination of MCP/CDL and PAT allows us to acquire single photons with high spatial and time resolution. Spatial resolution at the detector's active surface is projected to be 30 microns. The absolute timing accuracy achieved to date is 200 ps. The projected maximum count rate is about 2 million counts/sec. In addition, we are developing critical customized and optimized data processing techniques, information extraction algorithms, and visualization methods to exploit the data and information generated by the RULLI sensor system.

Applications

RULLI is a relatively mature technology. We have demonstrated a number of applications under various field operation scenarios. Here are some examples of actual data and generic applications.

High Precision Topographical Mapping: This image shows the topography of a solid target measured in the laboratory. A very low-power pulsed laser was used to illuminate the target. The letters LANL were carved out of 2-inch thick Styrofoam block and attached to a solid piece of the same type of Styrofoam. A total of 280K photons are used to derive this topographical map. This image demonstrates the RULLI system's capability of remotely measuring precise topography from a single vantage point with no moving parts.

Probing Complex 3D Structures: This image displays a 2D projection of the three dimensional distribution of detected photons reflected from a Ponderosa pine. The pine tree was illuminated from a distance with a low-power pulsed laser which was colocated with the stationary sensor. The data is contained in a cubical volume with 13 m on the side. The blue square defines the viewing direction into the data volume. A total of 2.8 million photons is contained in this volume. Detailed complex structure of the tree is clearly revealed by this measurement.

The salient features of the RULLI sensor system are as follows: single photon sensitivity, extremely low noise, ambient temperature operation, and non-pixellated contiguous imaging area. Specific advantages of the RULLI system's application to 3D imaging are: large area and simultaneous coverage, no moving parts, and low illumination power requirement.

Los Alamos, in collaboration with other institutions, is actively improving all aspects of the RULLI technology, exploring new single photon sensor concepts, and developing applications that take full advantage of this unique three dimensional sensor capability. For more technical information on RULLI and related technologies, contact rulli-poc@lanl.gov.

References

1. Baron, M. H., and Priedhorsky, W. C., "Crossed delay line detector for ground and space based applications," in EUV, X-Ray and Gamma-Ray Instrumentation for Astronomy IV, O.H. Siegmund, ed., Proc. Soc. Photo-Opt. Instrum. Eng. 2006, 188-197 (1993).
2. Priedhorsky, W. C., Smith, R. C., and Ho, C., "Laser ranging and mapping with a photon-counting detector," Applied Optics, 35, 441-452 (1996).
3. Ho, C., et al. "Demonstration of Literal Three-Dimensional Imaging," Applied Optics, 38, 1833-1840 (1999).

This is a Los Alamos Unclassified Report, LA-UR-01-1736.