Opto-Mechanical and Electronic Design of a Tunnel-Trap Si Radiometer

Area of Science:

• * Optical metrology and radiometry.
• * Semiconductor device physics and calibration standards.

Background:

• * Accurate spectral power and irradiance responsivity scales are crucial for optical measurements.
• * Existing radiometers face limitations in sensitivity, field-of-view, and cosine response.

Purpose of the Study:

• * To develop a transmission-type light-trap silicon radiometer for maintaining NIST spectral responsivity scales.
• * To achieve high sensitivity and accurate cosine response for optical radiation measurements.
• * To improve the calibration of illuminance and irradiance meters.

Main Methods:

• * Fabrication of a silicon radiometer with replaceable apertures and parallel-connected photodiodes in a light-trap configuration.
• * Elimination of beam clipping within an 8° field-of-view (FOV) using a triangular tunnel design.
• * Frequency compensation applied to the photocurrent-to-voltage converter for optimized gain characteristics.

Main Results:

• * The developed trap radiometer maintains NIST spectral power and irradiance responsivity scales from 406 nm to 920 nm.
• * Achieved high sensitivity with noise-equivalent-power as low as 47 fW (dc) and 5.2 fW (10 Hz chopping).
• * Demonstrated excellent cosine responsivity with relative deviations ≤ 0.02% within 5° FOV and 0.05% at 8° FOV.

Conclusions:

• * The transmission-type light-trap silicon radiometer serves as a reliable transfer standard for optical radiation.
• * It enables direct calibration of illuminance and irradiance meters, enhancing accuracy in SI unit traceability.
• * The device offers improved performance in sensitivity and angular response compared to conventional radiometers.