L-1 Standards and Technology, Inc. Primary Standards, Radiometry & Space



Photodiode Trap Detector Model LTD-10 User Manual (pdf)

L-1 Trap Detectors are high efficiency, standards grade detectors capable of measurements with 0.1% uncertainty  when uncalibrated and 0.01% uncertainty when calibrated against an absolute standard such as the L-1 CryoRad III cryogenic radiometer. A low noise, high gain precision transimpedance amplifier such as the L-1 TIA enables such low uncertainty measurements.


The LTD-10 consists of 3 Hamamatsu 1337 windowless silicon photodiodes arranged in a retroreflecting, ‘trap’, configuration. This configuration greatly enhances the overall efficiency of the detector to well beyond that of a single silicon photodiode.  An uncoated silicon photodiode has an index of refraction of approximately 3.5 and reflects approximately 30% of incident light. By increasing the number of detectors and adding their photocurrents, the number of reflections increases and the quantum efficiency of the device is enhanced. By increasing the number of reflections to five, the total light lost due to Fresnel reflections is decreased to 0.24% which, in turn, corresponds to an effective quantum efficiency of 99.76% for the entire detector. These detectors are also highly uniform and exhibit a nonuniformity of 0.02% peak to valley when scanned with a 250 micrometer spot size.


LTD-10 trap detectors have a 7mm diameter input opening for power level measurements. Radiance measurements are enabled by the installation of precision apertures over the front face of the detector. This operation is able to be performed by the user and is as simple as tightening two button head cap screws (2-56) to secure the aperture into place. Two tapped holes (1x 4-40 & 1x 8-32) populate the underside of the detectors for mounting to a post or baseplate, both of which are included your purchase of an LTD-10. To maintain a clean environment within the detector housing while the aperture is open and the detectors are exposed, a purge fitting is installed on the rear of the detector for purging the detector with pure, dry nitrogen at a flow rate of around 0.5 liters per minute.


A calibrated LTD-10 trap detector enables simple and highly accurate irradiance, radiance, and power level measurements. Owning an LTD-10 means your lab has the capability to make calibrated transfer standard optical measurements with a detector having a compact form factor and fast response time.

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