Nonlinearity Measurements of High-Power Laser Detectors at NIST

We briefly explain the fundamentals of detector nonlinearity applicable to both electrical and optical nonlinearity measurements. We specifically discuss the attenuation method for optical nonlinearity measurement that the NIST system is based upon, and we review the possible sources of nonlinearity inherent to thermal detectors used with high-power lasers. We also describe, in detail, the NIST nonlinearity measurement system, in which detector responsivity can be measured at wavelengths of 1.06 µm and 10.6 µm, over a power range from 1 W to 1000 W. We present the data processing method used and show measurement results depicting both positive and negative nonlinear behavior. The expanded uncertainty of a typical NIST high-power laser detector calibration including nonlinearity characterization is about 1.3 %.     

Measurement of the nonlinearity of Ge-and InGaAs-photodiodes at high irradiance levels

We present the measurements and the analysis of nonlinearity of Ge- and InGaAs-photodiodes responsivity measured at high irradiance levels (up to ～ 90 mW / mm²) in the near infrared. The nonlinearity was measured using a fiber-optics-based setup which employs the Differential Spectral Responsivity (DSR) technique. The measurements of the nonlinearity were carried out at different laser beam diameters with fiber optic attachment as well as open-beam. All photodiodes investigated present a nonlinarity of the saturation type, which depends on the beam diameter of the radiation source.     

Realization of ITS-90 Above the Silver Point at the NIM

The high-temperature primary standard system was gradually improved at the National Institute of Metrology (NIM) in China after 2004. A new primary standard pyrometer (PSP) was developed, one with a size-of-source effect of 1 × 10^?4, and regional thermostats for interference filters, photoelectric detectors, and I/V converters. The relative spectral responsivity of the entire PSP was calibrated by means of a new facility. A new LED-based measurement facility and novel systematic error correction model were utilized to characterize the PSP nonlinearity and extend the photocurrent to PSP temperature readings of about 2680 °C. As an improved scheme, the fixed-point blackbody pyrometer assembly was utilized to realize and disseminate the International Temperature Scale of 1990 above the silver point. This scheme can avoid the influences of instability and inhomogeneity of tungsten strip lamps and corrects pyrometer drifts, thereby improving the realization uncertainty and simplifying the transfer chain. The expanded uncertainties of the scale realization ranged from 0.04 °C at the silver point to 0.48 °C at 2474 °C.     

Nonlinearity measurements of silicon photodetectors

Nonlinearities of the responsivity of various types of siliconphotodetectors have been studied. These detectors are based onphotodiodes with two sizes of the active area (10 x 10 mm(2) and 18 x 18 mm(2)). The detectorconfigurations investigated include single photodiodes, two reflectiontrap detectors, and a transmission trap detector. For all devices, the measured nonlinearity was less than 2 x 10(-4) forphotocurrents up to 200 muA. The diameter of themeasurement beam was found to have an effect on thenonlinearity. The measured nonlinearity of the trap detectorsdepends on the polarization state of the incident beam. Theresponsivity of the photodetectors consisting of the large-areaphotodiodes reached saturation at higher photocurrent values comparedwith the devices based on the photodiodes with smaller activearea.     

Correction of photoresponse nonuniformity for matrix detectors based on prior compensation for their nonlinear behavior

What we believe to be a novel procedure to correct the nonuniformity that is inherent in all matrix detectors has been developed and experimentally validated. This correction method, unlike other nonuniformity-correction algorithms, consists of two steps that separate two of the usual problems that affect characterization of matrix detectors, i.e., nonlinearity and the relative variation of the pixels' responsivity across the array. The correction of the nonlinear behavior remains valid for any illumination wavelength employed, as long as the nonlinearity is not due to power dependence of the internal quantum efficiency. This method of correction of nonuniformity permits the immediate calculation of the correction factor for any given power level and for any illuminant that has a known spectral content once the nonuniform behavior has been characterized for a sufficient number of wavelengths. This procedure has a significant advantage compared with other traditional calibration-based methods, which require that a full characterization be carried out for each spectral distribution pattern of the incident optical radiation. The experimental application of this novel method has achieved a 20-fold increase in the uniformity of a CCD array for response levels close to saturation.     

Intensity-ratio error compensation for triangular-pattern phase-shifting profilometry

We present an intensity-ratio error-compensation method to decrease the measurement error caused by projector gamma nonlinearity and image defocus in triangular-pattern phase-shifting profilometry. The intensity-ratio measurement error is first determined by simulating the measurement with the triangular-pattern phase-shifting method with ideal and real captured triangular-pattern images based on the ideal and real gamma nonlinearity functions. A lookup table that stores the intensity-ratio measurement error corresponding to the measured intensity ratio is constructed and used for intensity-ratio error compensation. Experiments demonstrated that the intensity-ratio error compensation method significantly reduced the measurement error in the triangular-pattern phase-shifting method by 28.5%.     

Thermodynamic-temperature determinations of the Ag and Au freezing temperatures using a detector-based radiation thermometer

The development of a radiation thermometer calibrated for spectral radiance responsivity using cryogenic, electrical-substitution radiometry to determine the thermodynamic temperatures of the Ag- and Au-freezing temperatures is described. The absolute spectral radiance responsivity of the radiation thermometer is measured in the NIST Spectral Irradiance and Radiance Responsivity Calibrations using Uniform Sources (SIRCUS) facility with a total uncertainty of 0.15% (k=2) and is traceable to the electrical watt, and thus the thermodynamic temperature of any blackbody can be determined by using Planck radiation law and the measured optical power. The thermodynamic temperatures of the Ag- and Au-freezing temperatures are determined to be 1234.956 K (+/-0.110 K) (k=2) and 1337.344 K(+/-0.129 K) (k=2) differing from the International Temperature Scale of 1990 (ITS-90) assignments by 26 mK and 14 mK, respectively, within the stated uncertainties. The temperatures were systematically corrected for the size- of-source effect, the nonlinearity of the preamplifier and the emissivity of the blackbody. The ultimate goal of these thermodynamic temperature measurements is to disseminate temperature scales with lower uncertainties than those of the ITS-90. These results indicate that direct disseminations of thermodynamic temperature scales are possible.     

Absolute Radiation Thermometry in the NIR

A near infrared (NIR) radiation thermometer (RT) for temperature measurements in the range from 773 K up to 1235 K was characterized and calibrated in terms of the “Mise en Pratique for the definition of the Kelvin” (MeP-K) by measuring its absolute spectral radiance responsivity. Using Planck’s law of thermal radiation allows the direct measurement of the thermodynamic temperature independently of any ITS-90 fixed-point. To determine the absolute spectral radiance responsivity of the radiation thermometer in the NIR spectral region, an existing PTB monochromator-based calibration setup was upgraded with a supercontinuum laser system (0.45 \(\upmu \hbox {m}\) to 2.4 \(\upmu \hbox {m}\)) resulting in a significantly improved signal-to-noise ratio. The RT was characterized with respect to its nonlinearity, size-of-source effect, distance effect, and the consistency of its individual temperature measuring ranges. To further improve the calibration setup, a new tool for the aperture alignment and distance measurement was developed. Furthermore, the diffraction correction as well as the impedance correction of the current-to-voltage converter is considered. The calibration scheme and the corresponding uncertainty budget of the absolute spectral responsivity are presented. A relative standard uncertainty of 0.1 % \((k=1)\) for the absolute spectral radiance responsivity was achieved. The absolute radiometric calibration was validated at four temperature values with respect to the ITS-90 via a variable temperature heatpipe blackbody (773 K ...1235 K) and at a gold fixed-point blackbody radiator (1337.33 K).     

光学倍频影响激光外差干涉测量精度的机理

为了同时提高激光外差干涉测量的分辨力和精度,必须深入分析光学倍频对激光外差干涉测量精度的影响机理。在此基础上,建立了光学倍频相位测量模型,从理论上证明,光学倍频能够实现对激光外差干涉信号的细分,提高测量分辨力。光学倍频改变非线性误差的相位而使非线性误差减小,但同时改变了激光干涉多普勒频移的v/c平方项,使得残余累计误差增大。仿真结果表明,光学N倍频使非线性误差减小到原来的1/N,但使残余累计误差增大N2倍。因此,光学倍频仅适用于低速测量的场合。     

CMOS photodetectors for industrial position sensing

The properties of a CMOS-compatible pn-photodiode, phototransistor, and one-dimensional lateral-effect photodiode (LEP) for position-sensing applications are characterized. The photodiode and phototransistor seem to have properties that are comparable to typical commercial photodetectors despite the relatively large variations in their spatial and spectral responses and the lower responsivity in the near-infrared band. In addition to the above properties the LEP's show excellent linearity, but 3-4 times larger NEP than corresponding commercial LEP's due to low resistance of the current dividing layer. The responsivity variations have no effect on the linearity of the LEP, and the slightly lower responsivity at near-infrared has only a negligible effect on the achievable resolution (SNR). These properties, usually considered as weak points of CMOS-compatible photodetectors, are believed to have little or no effect on the properties of a position sensor, if the diameter of the light spot is small (<100 μm). CMOS-compatible photodetectors are therefore believed to be very suitable for industrial position-sensing applications     

Sampling period criterion in a scanning-beam technique

The scanning-beam technique for measuring the response of a detector to an irradiance is analyzed. With this method the irradiance responsivity is determined by integration of the spatial responsivity. Since in practice the integration is approximated by a summation over steps with a finite step size, errors are introduced. It is shown both theoretically and experimentally that the error vanishes when the reciprocal step size lies beyond the diffraction limit. Furthermore, comparison shows that experiment and theory are in good agreement.     

A linearization method for commercial Hall-effect currenttransducers

The need for high-current transducers featuring wide-band and high-insulation levels is becoming a more and more impelling need in the electric power network, as the current distortion increases due to the proliferation of nonlinear, time-variant loads. The closed-loop Hall-effect current transducers show a good compromise between cost and metrological performance. On the other hand, they may introduce an unacceptable nonlinearity error when the dynamic range of the input current is a reduced portion of the dynamic range of the transducer and may show a large drift of their gain with temperature. The paper proposes a simple method for reduction of the nonlinearity error when the input signal is an unbiased sinewave and the automatic calibration of the gain. Experimental results are also reported, showing the method effectiveness     

Development of a New InGaAs Radiation Thermometer at NMIJ

The first InGaAs radiation thermometer at NMIJ was developed more than ten years ago as a standard radiation thermometer operating from 150 to 1,100°C. Its size-of-source effect (SSE) was as large as 1% from 6 mm in diameter to 50 mm in diameter. The new thermometer has an SSE of 0.3%. The reason for the error in measuring the SSE of InGaAs thermometers was also found. The new thermometer at first suffered from nonlinearity and the distance effect (DE). These deficiencies arose from the misalignment of optics inside the thermometer and were solved by increasing the detector size from 1 mm in diameter to 2 mm in diameter. Unfortunately, the detector of 2 mm diameter had a smaller S/N ratio than that of the 1 mm one at the indium (In) point. The final design uses a detector of 1 mm diameter, but the radiation is focussed on a smaller area of the detector. The new thermometer is smaller and lighter than preceding designs and other standard InGaAs radiation thermometers. The temperature of the main part of the instrument, including the filter, the detector, and the preamplifier board, is controlled at 30°C. In addition to the calibration with the six fixed points of copper (Cu), silver (Ag), aluminum (Al), zinc (Zn), tin (Sn), and indium (In), the linearity from the In point to the Cu point, the SSE, the DE, and the spectral responsivity were measured.     

Polarization Effects in Heterodyne Interferometry

Abstract

A detailed analysis of the polarization effects which lead to nonlinearity in the non-ideal optical heterodyne interferometer is presented. Extensive use is made of the coherency matrix representation by setting up a ‘cross-coherency matrix’ representation. A generalized treatment of periodic phase errors (nonlinearity) is then presented. Individual contributions to the nonlinearity have been characterized as either ‘independent’ or ‘dependent’ phase errors. In the single-pass plane-mirror heterodyne system, to which the approach is applied, phase errors for rotational misalignment of the nominally orthogonal linearly polarized input states, beam splitter leakage, non-orthogonality, ellipticity and the effect of misaligned polarizer-mixer are explicitly considered. The latter effect is found to produce nonlinearity only when in combination with any one of the first three and is therefore a dependent phase error. The nonlinearity arising from ellipticity is identical with that from rotational misalignment except that it has an offset. Rotational misalignment and ellipticity produce nonlinearity at the second harmonic and are second order for practical set-ups. It is also found that combinations of positive (anticlockwise) and negative (clockwise) angular misalignments of the azimuth of the states, non-orthogonality and misorientations of the polarizer-mixer, all relative to the polarizing beam splitter axes, lead to different peak-to-peak nonlinearities in the given system.     

Facility for spectral irradiance and radiance responsivity calibrations using uniform sources

Detectors have historically been calibrated for spectral power responsivity at the National Institute of Standards and Technology by using a lamp-monochromator system to tune the wavelength of the excitation source. Silicon detectors can be calibrated in the visible spectral region with combined standard uncertainties at the 0.1% level. However, uncertainties increase dramatically when measuring an instrument's spectral irradiance or radiance responsivity. We describe what we believe to be a new laser-based facility for spectral irradiance and radiance responsivity calibrations using uniform sources (SIRCUS) that was developed to calibrate instruments directly in irradiance or radiance mode with uncertainties approaching or exceeding those available for spectral power responsivity calibrations. In SIRCUS, the emission from high-power, tunable lasers is introduced into an integrating sphere using optical fibers, producing uniform, quasi-Lambertian, high-radiant-flux sources. Reference standard irradiance detectors, calibrated directly against national primary standards for spectral power responsivity and aperture area measurement, are used to determine the irradiance at a reference plane. Knowing the measurement geometry, the source radiance can be readily determined as well. The radiometric properties of the SIRCUS source coupled with state-of-the-art transfer standard radiometers whose responses are directly traceable to primary national radiometric scales result in typical combined standard uncertainties in irradiance and radiance responsivity calibrations of less than 0.1%. The details of the facility and its effect on primary national radiometric scales are discussed.     

探测器响应度不均匀性对测量LED平均发光强度的影响

使用响应度分布不均匀的探测器来测量光分布不均匀LED的平均发光强度时,其测量结果可能会引入显著的测量误差。设计实验装置对3种不同类型的探测器的响应度分布进行测量,结果表明带光漫射器的光度探测器响应度均匀性很差,这样的光度探测器用于测量一种白光LED平均发光强度时,响应度不均匀引起的测量误差可达2.0%。类似于光谱失配修正方法,给出了对探测器响应度不均匀性评价的方法以及响应度不均匀性评价因子c的表达式,并建议在进行LED平均发光强度测量时,应避免使用带光漫射器的光度探测器。     

Identification and correction of analog-to-digital-converter nonlinearities and their implications for differential absorption lidar measurements

Differential absorption lidar (DIAL) is a powerful remote-sensing technique widely used to probe the spatial and temporal distribution of ozone and other gaseous atmospheric trace constituents. Although conceptually simple, the DIAL technique presents many challenging and often subtle technical difficulties that can limit its useful range and accuracy. One potentially serious source of error for many DIAL experiments is nonlinearity in the analog-to-digital converters used to capture lidar return signals. The impact of digitizer nonlinearity on DIAL measurements is examined, and a simple and inexpensive low-frequency dithering technique that significantly reduces the effects of ADC nonlinearity in DIAL and other applications in which the signal is repetitively averaged is described.     

An Investigation of the Linearity of Standard Thermistor Wattmeters and an Estimate of the Minimum Attainable Errors of Measurements of the Ratio of Microwave Powers

The results of experimental investigations of the nonlinearity of thermistor power converters are presented and the main components of the error in measuring nonlinearity in a differential microcalorimeter are analyzed. The resultant error in determining nonlinearity does not exceed 0.002 dB/10 dB at frequencies up to 18 GHz.     

Adaptive compensation for position error signal nonlinearity

The magnetoresistive (MR) magnetic head is a poor positioning transducer for a disk file's servo control system because its positioning response is nonlinear with radial displacement. This paper shows how the MR head's poor positioning properties are alleviated by a self-adjusting adaptive algorithm that allows a disk file to linearize its own servo position error signal (PES). The adaptive linearizer uses a nonlinear state estimator whose nonlinearity adjusts to match the nonlinearity of the PES. As the match between the two nonlinearities adaptively improves, the state estimator gives increasingly accurate estimates of the true actuator position     

交叉调制对电桥平衡的影响及其抑制方法的研究

详细讨论了由于电桥指零仪系统的非线性而产生的谐波交叉调制效应对电桥平衡的影响,设计并制作了一种高Q值的谐振滤波器以抑制此效应的影响。谐振滤波器的电感线圈采用高导磁率的瓷罐型铁芯绕制而成,通过调节两个瓷罐的间隙的大小以获得最大的Q值,从而降低由于铁芯损耗产生的热噪声。实验结果表明,该谐振滤波器的等效输入噪声小于1nV/Hz ,采用该滤波电路后,交叉调制效应造成的影响被有效降低了两个数量级以上。