Silicon radiometer whose response is independent of operating temperature David D. Royston, Zhiyuan Geng, and Jianguo Liu

David Royston is with U.S. National Center for Devices and Radiological Health, Rockville, Maryland 20857; the other authors are with Beijing Opto-Electronic Institute, Laser Parameter Testing Center, Beijing, China. Received 15 December 1983. A laser hazard measuring instrument was designed and

built by National Center for Devices and Radiological Health personnel.1 This microprocessor based instrument measures levels of visible and near-IR laser radiation and determines the exposure duration over which these levels are below Class I Accessible Emission Limits.2 Class I levels of laser radiation are not considered hazardous. The instrument uses a pla­nar-diffused oxide-passivated silicon photodiode (United Detector Technology model PIN-10D). The photodiode is operated in the photovoltaic (nonbiased) mode. The in­strument can measure pulsed or cw laser radiation. It can also measure ambient background levels and automatically correct subsequent laser level measurements. Measured background includes the contribution of offset voltage in the input am­plifiers (always a positive value), any optical background, and detector dark current. Typical background levels were 0.1% of the signal levels. Previous testing3 has shown that silicon photodiodes have a temperature dependence (-0.1%/oC for visible wavelengths) which must be taken into account for accurate visible radiation measurements. Additional testing4

has also shown that some silicon detector instruments have a temperature dependence of 20% over a 44°C range between 4 and 48°C. Since this instrument is needed for field use, it was also tested for temperature dependence.

The temperature range chosen and experiment were iden­tical to those of Ref. 4. The reference instrument was a high-precision (0.1%) twin calorimeter (Calorimetrics model MC2-P). The test level to the photodiode was ~350 μW of . 633-nm laser radiation, and the level to the reference calo­rimeter was 14 mW. The reference calorimeter operated at a room temperature of 22°C during the temperature depen­dence test. Ratios of the instruments response to the calo­rimeter's response were taken in 11°C increments from 4 to 48°C. These data were then normalized to 22°C. Results are shown in Fig. 1 for both the detector and the signal pro­cessing electronics in the environmental chamber (two trials) and the detector alone in the environmental chamber (one

Fig. 1. Temperature dependent response of a PIN silicon photodiode detector head and instrument to 632.8-nm laser radiation.

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trial). The results indicate that the instrument has no tem­perature dependence and that the silicon detector's response varied by <2% over the entire temperature range. Based on these tests, the response of planar silicon detectors to 633-nm radiation is essentially constant over the temperature range of 4-48°C.

The mention of commercial products or their use in con­nection with material reported herein is not to be construed as either an actual or implied endorsement of such products by the Food and Drug Administration.

References

1. J. Silberberg, in Proceedings, Electro-Optics/Laser 81 Conference (Industrial & Scientific Conference Management, Chicago, 1981).

2. Federal Performance Standard for Light Emitting Products (21CFR.1040.10)

3. B. 0. Kelly, in Proceedings, National Conference on Measure­ments of Laser Emissions for Regulatory Purposes.

4. R. J. Landry and R. W. Peterson, Appl. Opt. 16, 2968 (1977).

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