The ultraviolet (UV) light at 222nm can be absorbed by microbial DNA and RNA, changing their structures and achieving the effect of sterilization. Unlike commonly used UVC light, 222nm UV light is harmless to humans, making it a crucial role in disinfection and sterilization. Consequently, calibration of 222nm UV radiometers is also of great significance. In this paper, according to the characteristics of KrCl excimer lamp, the effects of different types of filters on the spectrum of sterilization lamp are studied, as well as the calibration method of UV radiometer, and the measurement uncertainty is evaluated.
Ultraviolet radiant exposure meter, also known as UV energy meter, is widely used in a multitude of fields, such as sterilization, climate change, solar photovoltaic, material aging, medical health, UV curing, lithography and so on. Ultraviolet exposure radiation meter is a commonly used instrument to measure ultraviolet radiation. Due to the particularity of the structure and the complexity of the influencing factors, the measurement error of commercial instruments is very high. Commonly used ultraviolet light sources include mercury lamps, LED light sources, metal halogen lamps and so on. This paper will study the calibration method of the ultraviolet exposure radiation meter, and evaluate the measurement uncertainty.
The nonlinear effect is one of the characteristics of photodetectors. In infrared measurement systems, photodetectors like MCT, InGaAs and InSb are widely used; while their non-linearity is still a problem. National Institute of Metrology, China has built an infrared spectral radiance measurement system. The system consists of a variable temperature blackbody as the standard radiation source; and uses a Fourier transform Infrared Spectrometer as the measuring instrument, including a MCT detector which is the main source of non-linearity uncertainty. In this study, an interpolation method and a polynomial fitting method are used to correct the non-linearity of the measurement system. To do so, at first, set the temperature of the standard variable blackbody to a serial of different temperatures, and use the measurement system to acquire the spectral response signal at each temperature; then, calculate the spectral radiance value of the standard radiation source based on the Planck’s law; after that, in the spectral dimension, analyze the relationship between and , and correct its non-linearity with a piecewise linear interpolation method and a multi-order polynomial fitting method; finally, verify the above two methods and analyze the relative deviation accordingly. The results show, the deviation is relatively large in wavelength range smaller than 8μm; while in 8μm~14μm wavelength range, the relative deviation is around 0.5%~0.001% and around 1.0%~0.001% by using the piecewise linear interpolation method and polynomial fitting method, respectively.
UV radiometers are used in many areas. There are many kinds of UV light sources with different peak wavelength and different wavelength range. The broadband UV radiometers are wildly used due to easy to use and low cost. However, there are some obvious disadvantages for the broadband radiometers. They cannot distinguish the spectral characteristics of UV sources. That will cause the spectral mismatch measurement error for the UV broadband radiometers calibration. Recently, the fiber spectroradiometer plays a more and more important role in this area. The fiber spectroradiometer is more portable and low cost compared to the double grating spectroradiometer. We can obtain the spectral characteristics and any UV irradiance using the fiber spectroradiometer. However, for most fiber spectroradiometers, we cannot use them to replace the UV broadband radiometers for the absolute irradiance measurement. There are four key effects for that. The first one is the stray light. Stray light effect is obvious for the fiber spectroradiometer, especially in the UV wavelength range. The second one is the temperature effect. The third one is the non-linearity effect. The fourth one is the bandwidth effect. This effect will cause the measurement error for the spectral distribution of the UV source. In this paper, we research the four factors that reduce the measurement accuracy of the fiber spectroradiometer in UV wavelength range.
In order to achieve the goal of spectral radiance (SR) and spectral irradiance (SI) calibration with an uncertainty of less than 1.0%, NIM set up a MC-C large-area high-temperature fixed point blackbody(HTFP BB) as the new generation of SR and SI reference source, which is composed of large WC-C fixed point cell and BB3500MP. It can be used directly for the SR and SI realization, thereby further reducing measurement uncertainty. The HTFP BB with WC-C fixed point has excellent stability, reproducibility and repeatability in the high temperature range of more than 3020K, which greatly improves the detection capability in the ultraviolet range (UV). Accurate measurement of melting temperature of HTFP BB is an important source of error, which is determined as the point of inflection (POI) of melting plateau. At the same time, POI is also an important reference point used in comparison experiments. Different calculation methods introduce different degrees of errors, which are critical. This paper studied the current three POI numerical calculation methods, namely “differential+second-order fitting” (DSF), “third-order direct fitting” (TDF), “histogram+Gaussian fitting” (HGF). The numerical calculation of the POI was performed on the data of WC-C14 and Re-C measured at NIM and WC-C14 and WC-C10 measured at VNIIOFI by the above three methods. Combining the fitting results and correlation coefficients to explore the characteristics of each method. Based on the experimental results, a more reasonable calculation method is proposed to reduce the calculation error of the POI of the previous data to less than 5 mK.
With the highly accurate calibration requirements of ocean remote sensing, it is crucial to provide long-term in-situ measurement and validation for on-orbit remote sensors by using sea-based validation sites. However, when the laboratory-calibrated spectroradiometer is transmitted to in-situ validation sites, the measurement results are greatly deviated due to the difference between the field and the calibration environment, which directly affects the accuracy of on-orbit remote sensors synchronous calibration. In this paper, both of above water measurement and undersea profile measurement are considered. The temperature effects and stray light characteristics of common spectrometers were studied. In addition, the characteristics of the classic calculation model and optimization calculation model of immersion factor are compared and analyzed.
The absolute measurements of spectral radiance, irradiance and intensity in infrared wave range are very important for infrared target recognition, material emissivity measurement and so on. Recently, many researchers focus on how to accurately measure absolute infrared spectral radiation, in which one key point is how to suppress stray radiation. In this paper, an absolute infrared spectral radiance measurement system was built up. The system contained a fixed-point blackbody source, a variable temperature blackbody source, a radiant source to be measured, Fourier Transform Infrared Radiometer (FTIR), optical system, non-contact infrared thermometer and so on. Emissivities of the standard source and the radiant source to be measured are 0.999 and 0.995, respectively. According to Planck’s law, their absolute spectral radiance should be similar at the same radiation temperature. In experiment, temperatures of the standard blackbody and radiant source to be measured were set to 500°C, and the FTIR was used to measure spectral radiance. The results show spectral radiance of the standard source is 14.9% smaller than the radiant source to be measured at 10μm wavelength. A thermal infrared imager and optical simulation software were used to analyze the possible reasons. To solve the problems, a shielding plate and a field aperture was installed respectively at the entrance of the optical system and before the FTIR to suppress stray radiation. Moreover, sizes and positions of the shielding plate, optical system, and field aperture were analyzed by optical simulation software and mathematical calculation. After optimization, the experimental results show the difference of spectral distributions between the standard source and the radiant source to be measured is only 1.42% at 10 μm wavelength, suggesting stray radiation is effectively suppressed in the system.
The absolute measurement of infrared spectral radiance is very important for optical radiometry. In this paper, a system for absolute measurement of infrared spectral radiance is built up. The system consists of fixed-point blackbody sources, a variable temperature blackbody, a radiant source to be measured, Fourier Transform Infrared Radiometer (FTIR), relay optical system, non-contact infrared thermometer and so on. The emissivity of the variable temperature blackbody is 0.999; the temperature range is 50°C ~ 1050°C. The emissivity of the radiant source to be measured is larger than 0.995; the temperature range is 30°C ~ 550°C. The variable temperature blackbody source was calibrated and can be traced to the fixed-point blackbody source. In experiment, it was used as the standard radiant source. The spectral range of this system is 3 μm ~ 14 μm. A serial of experiments have been implemented to analyze the uncertainty of each component, including the repeatability, size-of-source effect, stability, uniformity and so on. To improve the system’s uncertainty, we have suppressed stray radiation and optimized optical system by installing a water-cooled aperture and a field stop at the entrance of the optical system and before the FTIR, respectively; optimizing the system based on optical simulation and replacing the reflective mirrors with one off-axis parabolic mirror. Next step, we will re-evaluate the uncertainty of the improved system.
Deuterium lamp is used as the transfer standard of air-UV spectral irradiance (200nm to 400nm). The CCPRK1. b comparison of spectral irradiance 200nm to 350nm took deuterium lamp as transfer standard lamp. Spectral irradiance is measured by a spectroradiometer with finite bandwidth. The bandwidth can cause measurement error. In order to correct the measurement error, we apply SS and DO bandwidth correction methods to the spectrum of Deuterium lamp. We obtain the correction effect preliminarily.
CCD based array spectrometers are widely applied in remote sensing, earth observation, and other industries. However, the signals of ultraviolet region are very weak. Thus, the stray light is one of the most important factors on accurate measurements. In this work, the in-range stray light of commercial UV/VIS CCD array spectrometer and VIS/NIR CCD spectrometer were corrected by mathematical correction method. The measured stray light value at any pixel is of the order of 10−3 ~10−5 of the true in-range. A reduction of the stray light effect by 1-2 orders of magnitude can be achieved using a correction matrix based on line-spread functions (LSFs), which can be determined with the help of spectrally tunable lasers. On the other hand, the bandwidth of the commercial CCD array spectrometer was corrected due to the increasing needs for high accurate calibration and measurement of spectral radiometry. The correction outcome is in good agreement with the measured results by monochromator spectroradiometer.
In photometry and radiometry, photodetectors such as silicon detector and PMT detector are widely used. In precision metrology, the uncertainty of the nonlinearity should be considered. Superposition method is used to analyse the linearity. The silicon trap detector is measured using both nonmochromator light and monochromator light. First, integrating sphere with broadband light is used to test the linearity. The result shows that the nonlinearity is (1-3)×10-4 from 1uA to 1mA. The monchromator light result shows that the nonlinearity is below 3×10-4 from 1uA to 1mA, which is consistent with the integrating sphere method. For the PMT detector, the linearity is measured only using monochromator light. Experiment shows that the nonlinearity is less than 1×10-3 through three orders of magnitude.
Stray light due to the array spectroradiometer characteristic can’t be ignored in the ultraviolet region. In order to obtain a true spectral power distribution, stray light correction must be considered. Array spectraradiometer covering 200nm- 460nm is investigated using lasers and filters. First, several lasers are measured using the array spectroradiometer. Due to the fact that the wavelengths of the lasers are beyond the capabilities of the spectroradiometer, the response in the UV region is originated from stray light. Results show that the stray light contribution is at the level around 2×10-5. In order to correct the stray light, filters with different bandpass wavelength are used to correct the stray light from different wavelength region. Results show stray light consistency using lasers and filters.
CCD array based spectrometers are widely used in radiometric measurements. Ambient temperature and nonlinearity effects are significant factors for high accuracy measurement in the field. Here, a temperature correction method for the CCD array spectrometers was developed, which calculated the spectrometer response at each pixel. The deviation between measured and calculated spectrometer responses at a randomly selected temperature is less than 1%. In addition, the radiant power nonlinearity effects were investigated by supplementary-light methods. The gain settings nonlinearity effect was evaluated using FEL-type transfer standard lamps. The nonlinearity correction coefficients were calculated and analyzed based on the experiment, respectively.
In 2011, new primary standard apparatus of spectral radiance was setup at Changping campus of NIM based on high temperature blackbody BB3500M and double-grating monochromator of M207D. The temperature of the BB3500M was measured by a LP4 thermometer with uncertainty of 0.64 K at the temperature of 2980 K, which was calibrated by the Pt-C and Re-C fixed point blackbodies, and checked by a WC-C fixed point blackbody. The consistency of the temperature at 3021 K was better than 70 mK between NIM and VNIIOFI. The image of the measuring source was focused on the entrance slit of the monochromator with magnification 1:1. A mask was put in front of the entrance slit to limit the target spot size of the tungsten strip and the water-cooled aperture was 0.6 mm wide by 0.8 mm tall rectangle. The solid angle of spectral radiance measurement was approximately 0.008 sr. Uncertainty of spectral radiance scale realization was analyzed in this paper. The source of the uncertainty scale includes repeatability of the signal ratio of the blackbody and the transfer lamp, lamp alignment, temperature measurement of HTBB, non-uniformity of HTBB source, instability of HTBB source, correction of different size of source (BB and lamp), nonlinearity of the measurement system, current passed through the transfer lamp, wavelength error, polarization effects, bandwidth etc. The measurement uncertainty (k=2) of spectral radiance was 1.8 % at 250 nm, 0.90 % at 400 nm, 0.64 % at 800 nm, and 1.3 % at 2500 nm respectively.
The fiber spectroradiometer is now widely used in the photometry and radiometry due to the convenience. Before use the calibration is usually traced back to the tungsten lamp with known spectral irradiance. However, the working condition may differ greatly from the calibration condition, such as the signal level, the spectrum shape, and et al. In the experiment, characteristics of the fiber spectroraidometer are investigated, such as the short time stability, the nonlinear phenomena due to the integration time and signal level. Uncertainty of the calibration is evaluated taking all the factors into account.
New primary standard apparatus of spectral radiance was setup at National Institute of Metrology (NIM) based on high temperature blackbody BB3500M in 2011. Wavelength range was extended to 220 nm - 2550 nm. The measurement uncertainty of temperature was 0.64 K (k=1) at 2980K traceable to the Ag, Cu, Co-C, Pt-C and Re-C fixed point blackbodies, and checked by a WC-C fixed point blackbody. Good consistency was obtained by using two different imaging optics with varied solid angle and different object distances, the relative deviation is less than ±0.4 % at all wavelengths. A set of characteristic experiments were designed and analyzed in this paper, such as alignment error and the influence of the different shape and size of the water-cooled precise aperture, the polarization effects etc. NIM participated spectral radiance international comparison APMP.PR-S6 by using this new developed apparatus in 2014 with measurement uncertainty (k=1) 0.95% at 250nm, 0.50% at 400nm, 0.41% at 800nm, and 0.80% at 2500nm respectively.
The quantum efficiency of photon counters can be measured with standard uncertainty below 1% level using correlated photon pairs generated through spontaneous parametric down-conversion process. Normally a laser in UV, blue or green wavelength range with sufficient photon energy is applied to produce energy and momentum conserved photon pairs in two channels with desired wavelengths for calibration. One channel is used as the heralding trigger, and the other is used for the calibration of the detector under test. A superconducting nanowire single photon detector with advantages such as high photon counting speed (<20 MHz), low dark count rate (<50 counts per second), and wideband responsivity (UV to near infrared) is used as the trigger detector, enabling correlated photons calibration capabilities into shortwave visible range. For a 355nm single longitudinal mode pump laser, when a superconducting nanowire single photon detector is used as the trigger detector at 1064nm and 1560nm in the near infrared range, the photon counting efficiency calibration capabilities can be realized at 532nm and 460nm. The quantum efficiency measurement on photon counters such as photomultiplier tubes and avalanche photodiodes can be then further extended in a wide wavelength range (e.g. 400-1000nm) using a flat spectral photon flux source to meet the calibration demands in cutting edge low light applications such as time resolved fluorescence and nonlinear optical spectroscopy, super resolution microscopy, deep space observation, and so on.
We validate the S-S method and the differential operator method through numerical simulations and experiments.
Using a LED with a bandwidth of about 10nm as light source, we measure the spectral irradiance of the LED
when the spectroradiometer bandwidth is 1nm and 5nm. The S-S method and the differential operator method
act on experimental results to identify the efficiency of the methods. Through our analysis, the correction
methods play significant roles in the spectral irradiance measurement. Especially, the correction methods are
necessary when the light source has a narrow bandwidth feature.
Comparing to the big-size scanning spectroradiometer, the compact and convenient fiber spectroradiometer is widely
used in various kinds of fields, such as the remote sensing, aerospace monitoring, and solar irradiance measurement.
High accuracy calibration should be made before the use, which involves the wavelength accuracy, the background
environment noise, the nonlinear effect, the bandwidth, the stray light and et al. The wavelength lamp and tungsten lamp
are frequently used to calibration the fiber spectroradiometer. The wavelength difference can be easily reduced through
the software or calculation. However, the nonlinear effect and the bandwidth always can affect the measurement
accuracy significantly.
Due to the development of micro-electronics in the field of multi-element optical detectors and fiber optics in the
communication technology, fiber spectroradiometer now are widely used in photometry and radiometry. For most of
time, the measurement environment may differ greatly from the experimental condition where calibration is made.
Mistake may arise in the measurement process. An investigation of the characteristics of the fiber spectroradiometer is
presented here, such as the plug and pull of the fiber optics, the bandwidth, the integration time and linearity, and short
time stability. Experiments show that the bandwidth can significantly affect the accuracy of the measurement. Different
from the conventional big-size scanning spectroradiometer, the measurement ability of the fiber spectroradiometer
should be restricted in some application field. In measuring the spectra with multiple peaks, appropriate bandwidth
spectroradiometer should be used.
We propose a four-level superradiant laser system based on Cs at 1469 nm corresponding to the transition of 7S1/2 and 6P3/2 with a 459.3 nm pumping laser. With density matrix method, we calculate the relative population probabilities at each level theoretically. In a steady state, when the Rabi frequency is set to 3.5 MHz, 5.1% atoms are at 7S1/2 level while 1.9% at 6P3/2 level, which leads to the population inversion between the two levels. We design the experiment setup for the superradiant laser. In the steady state, the average photon number in the cavity is 1.1 × 106. According to the further calculation, the power of output superradiant laser is 0.17 mW and the laser linewidth is 17 Hz. This calculation method can also be used in the area of optical metrology.
Lamps and lamp system are widely used in large quantities in an era. The evaluation and control of optical radiation hazards of lamps and lamp systems is far more complicated. A special measurement and traceability facility was set up at NIM (National Institute of Metrology, China) to evaluate the optical radiation safety of lamp and lamp system, which includes a double grating spectroradiometer OL750D with two different entrance systems of spectral radiance and spectral irradiance traceable to the national primary standard of spectral irradiance by a 1000W spectral irradiance standard lamp, 40W deuterium lamp and a standard diffuser plate. The technical requirements of the measurement instrumentation used for optical radiation safety evaluation including monochromator type, wavelength accuracy, input optics, spectral scan interval and calibration sources are recommended also in this paper. Spectral radiance of a series of LED electric torches and infrared sources were measured by using the new developed system, and potential radiation hazards of retinal blue light hazard and retinal thermal hazard are calculated and evaluated. The optical radiation hazards of some samples are listed in Risk Group 2 (Moderate-Risk).
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