Abstract
In 2014, White et al suggested to combine the measurement principle of the two primary standards for optical power measurements [1]; the cryogenic radiometer and the predictable quantum efficient detector (PQED). The result was the dual mode operated induced junction photodiode, for which the internal losses of the diode are estimated by comparing the two modes of operation, i.e. electrical substitution and photocurrent measurements. During the electrical substitution measurements, the optical power is found through the temperature at the diode, which is measured using a thermistor located close to the diode. The diode is cycled between electrical heating (forward bias) where the power is precisely defined, and optical heating (using the diode as a passive absorbing element). Since the initial demonstration, significant improvements in the room temperature dual mode measurements have been achieved, bringing the uncertainties close to that given by cryogenic radiometer. [2]
The measurement system presented in this work consists of an induced junction photodiode which is connected to a heat sink through a weak heat link. The module is placed in a vacuum chamber, and a laser beam (HeNe laser with a wavelength of 633 nm) is directed at the diode through an Ar-coated window. Building on the system from ref [2], we present an improved measurement setup where the electrical coupling and grounding considerations have been improved. This has resulted in more accurate estimates of internal losses over a broader dynamic range. The internal losses are position dependent, with an average of 0.00% ± 0.04% for optical power as low as 366 μW, compared to 0.08% ± 0.04% at 500 μW, as reported in [2]. The uncertainties are limited by the thermal non-equivalence between electrical and optical heating.
In this work we also propose an improved temperature drift compensation, resulting in a reduction of uncertainties by a factor of four compared to previously reported results [2]. In addition, refinements made in the data analysis provide a clearer and more transparent interpretation, facilitating a better understanding of system variability. These refinements have resulted in a robust methodology for estimating uncertainties which corresponds well with observed variation in the measurements. We also demonstrate the importance of propagating absolute uncertainties, as the observed standard deviation in the internal quantum deficiency depends on the relative position of optical power related to the electrical power even if the noise level is constant.
This work demonstrates increased absolute radiometric measurement capability of room temperature dual mode detectors with uncertainties as low as 0.04 % limited by the heat equivalence of the dual mode assembly design. Work is ongoing to design and produce dual mode modules with better heat equivalence. The dual mode method represent a robust absolute radiometric measurement of any type of photodiodes, not just limited to PQEDs, with the potential to bring self-calibration directly into instruments and remote locations over a wide spectral range.
References: [1] White, M. et al. (2014). Metrologia, 51(6), S245. [2] Ulset, M. et al. (2022). Metrologia, 59(3), 035008. Tuesday, June 11, 2024
Self-Calibration of Photodiodes using the Dual-Mode Method
In 2014, White et al suggested to combine the measurement principle of the two primary standards for optical power measurements [1]; the cryogenic radiometer and the predictable quantum efficient detector (PQED). The result was the dual mode operated induced junction photodiode, for which the internal losses of the diode are estimated by comparing the two modes of operation, i.e. electrical substitution and photocurrent measurements. During the electrical substitution measurements, the optical power is found through the temperature at the diode, which is measured using a thermistor located close to the diode. The diode is cycled between electrical heating (forward bias) where the power is precisely defined, and optical heating (using the diode as a passive absorbing element). Since the initial demonstration, significant improvements in the room temperature dual mode measurements have been achieved, bringing the uncertainties close to that given by cryogenic radiometer. [2]
The measurement system presented in this work consists of an induced junction photodiode which is connected to a heat sink through a weak heat link. The module is placed in a vacuum chamber, and a laser beam (HeNe laser with a wavelength of 633 nm) is directed at the diode through an Ar-coated window. Building on the system from ref [2], we present an improved measurement setup where the electrical coupling and grounding considerations have been improved. This has resulted in more accurate estimates of internal losses over a broader dynamic range. The internal losses are position dependent, with an average of 0.00% ± 0.04% for optical power as low as 366 μW, compared to 0.08% ± 0.04% at 500 μW, as reported in [2]. The uncertainties are limited by the thermal non-equivalence between electrical and optical heating.
In this work we also propose an improved temperature drift compensation, resulting in a reduction of uncertainties by a factor of four compared to previously reported results [2]. In addition, refinements made in the data analysis provide a clearer and more transparent interpretation, facilitating a better understanding of system variability. These refinements have resulted in a robust methodology for estimating uncertainties which corresponds well with observed variation in the measurements. We also demonstrate the importance of propagating absolute uncertainties, as the observed standard deviation in the internal quantum deficiency depends on the relative position of optical power related to the electrical power even if the noise level is constant.
This work demonstrates increased absolute radiometric measurement capability of room temperature dual mode detectors with uncertainties as low as 0.04 % limited by the heat equivalence of the dual mode assembly design. Work is ongoing to design and produce dual mode modules with better heat equivalence. The dual mode method represent a robust absolute radiometric measurement of any type of photodiodes, not just limited to PQEDs, with the potential to bring self-calibration directly into instruments and remote locations over a wide spectral range.
References: [1] White, M. et al. (2014). Metrologia, 51(6), S245. [2] Ulset, M. et al. (2022). Metrologia, 59(3), 035008. Tuesday, June 11, 2024