Invited Article: Advances in tunable laser-based radiometric calibration applications at the National Institute of Standards and Technology, USA

Abstract

Recent developments at the National Institute of Standards and Technology's facility for Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (SIRCUS) are presented. The facility is predicated on the use of broadly tunable narrow-band lasers as light sources in two key radiometric calibration applications. In the first application, the tunable lasers are used to calibrate the spectral power responsivities of primary standard detectors against an absolute cryogenic radiometer (ACR). The second function is to calibrate the absolute radiance and irradiance responsivities of detectors with uniform light sources, typically generated by coupling the laser light into integrating spheres. The radiant flux from the uniform sources is determined by the ACR-calibrated primary standard detectors. Together these sources and detectors are used to transfer radiometric scales to a variety of optical instruments with low uncertainties. We describe methods for obtaining the stable, uniform light sources required for low uncertainty measurements along with advances in laser sources that facilitate tuning over broader wavelength ranges. Example applications include the development of a detector-based thermodynamic temperature scale, the calibration and characterization of spectrographs, and the use of a traveling version of SIRCUS (T-SIRCUS) to calibrate large aperture Earth observing instruments and astronomical telescopes.

FIG. 1.

Schematic diagram of NIST’s SIRCUS setup. Reprinted with permission from Brown et al., Appl. Opt. 45, 8218 (2006). Copyright 2006 The Optical Society.

FIG. 2.

Radiance scan across an 8 mm diameter aperture on a 30 cm sphere used in the calibration of radiation thermometers.

FIG. 3.

The spectral responsivity of SIRCUS working standards, a UV working standard (yellow), a VisNIR Si tunnel trap detector (green), an InGaAs working standard (orange), and an extended InGaAs working standard (blue).

FIG. 4.

The EQE of 4 reference standard tunnel trap detectors.

FIG. 5.

Spectral responsivities of 5 InGaAs photodetectors from different vendors show large variations between different models.

FIG. 6.

Spectral responsivities of 4 InGaAs photodetectors from one vendor.

FIG. 7.

Temperature dependence of the InGaAs photodetectors’ responsivities given in Fig. 6. The detector responsivity was measured different temperature setpoints in 2 °C intervals from 20 °C to 30 °C. The responsivity is stable through much of the wavelength range and shows large, but consistent, changes near the band edges.

FIG. 8.

Schematic diagram of the LBO OPO system with a BiBO doubler.

FIG. 9.

Typical bandwidth of the signal (top) and the idler (bottom).

FIG. 10.

Stability of the signal wavelength vs. time at 916.41 nm.

FIG. 11.

Representative LBO OPO temperature (a), rotation (b), and distance (c) tuning curves.

FIG. 12.

Schematic diagram of the intracavity doubled OPO (top) and outlined photograph of the doubling cavity (bottom).

FIG. 13.

Plot of the LBO OPO doubler crystal temperature vs. wavelength as calculated using the SNLO software.

FIG. 14.

LBO OPO output power as a function of wavelength. Red diamonds for the signal, orange squares for the idler, blue triangles for the BiBO doubled signal, and brown circles for the intracavity doubled LBO.

FIG. 15.

Output pulse energy of an Ekspla Q-switched OPO system.

FIG. 16.

Spectral widths of the output of the kHz OPO system at 350 nm, 600 nm, and 1100 nm.

FIG. 17.

Oscilloscope traces of the LBO OPO relative output power before (top) and after (bottom) propagation through the 50 mm SIS. Reprinted with permission from Zong et al., Metrologia 49, S124-S129 (2012). Copyright 2012 IOP Publishing.

FIG. 18.

Time sequence of the measurement of a pulsed laser train. Reprinted with permission from Zong et al., Metrologia 49, S124-S129 (2012). Copyright 2012 IOP Publishing.

FIG. 19.

Schematic diagram of the kHz laser-based calibration system. Reprinted with permission from Zong et al., Metrologia 49, S124-S129 (2012). Copyright 2012 IOP Publishing.

FIG. 20.

Relative difference in measured responsivity between the electrometers and the trans-impedance amplifiers (blue diamonds) and between the kHz OPO-based calibration and the conventional calibration using cw lasers (red circles). Reprinted with permission from Zong et al., Metrologia 49, S124-S129 (2012). Copyright 2012 IOP Publishing.

FIG. 21.

Effect of laser power control on measurement fluctuations.

FIG. 22.

(a) Output from a multimode optical fiber excited with 532 nm radiation (left). Output from the same fiber with the “speckle-eater” turned on (right). (b) Effect of laser speckle on the measurement uncertainty, showing the difference in measurement noise when the speckle eater (an ultrasonic bath) is turned on and off.

FIG. 23.

Absolute spectral responsivity of a filter radiometer measured using cw, picosecond, and femtosecond lasers. Representative picosecond and femtosecond spectra are shown as well.

FIG. 24.

Expansion of Fig. 23 around 902 nm illustrating the difference in the measured responsivity using cw, picosecond, and femtosecond lasers, respectively.

FIG. 25.

Measurements of the EQE of a Si tunnel trap detector over 10 years.

FIG. 26.

Stability of InGaAs detectors over 6 years, measured on NIST’s Spectral Comparator Facility. Colored symbols represent the difference from the initial mean. The measurement uncertainties (k = 1) are shown in black with the connecting line.

FIG. 27.

Spatial uniformity of an InGaAs detector at (left) 900 nm, (middle) 1250 nm, and (right) 1600 nm. 0.2% contours are shown.

FIG. 28.

Comparison between measured (symbol) and modeled (symbol) EQEs of a Si tunnel trap detector.

FIG. 29.

ASR of the AP-1 and the spectral radiance of a primary standard gold melting point blackbody (at 1337.33 K).

FIG. 30.

Expanded view of the interference fringes seen in four determinations of the spectral responsivity of the AP1.

FIG. 31.

Repeat measurements of a gold-point blackbody by the AP-1. The mean temperature determined by the AP-1 measurements is compared with the ITS-90 temperature.

FIG. 32.

Semi-log plot of LSF’s acquired from a spectrograph with excitation wavelengths ranging from 350 nm to 800 nm. Reprinted with permission from Brown et al., Appl. Opt. 45, 8218 (2006). Copyright 2006 The Optical Society.

FIG. 33.

Stray light distribution matrix (SDM).

FIG. 34.

Stray light correction of a spectrograph’s measurements of (left) a green optical filter and (right) a green LED. Original measurement (black); stray light corrected measurement (green). (Top) Logarithmic scale; (bottom) linear scale. The dashed line corresponds to a signal level of 1 DN. Reprinted with permission from Zong et al., Proceedings of the International Commission on Illumination D2, 33–36 (2007). Copyright 2007 CIE.

FIG. 35.

Experimental setup for SIRCUS laser-based calibration of Suomi NPP VIIRS. The SIRCUS integrating sphere is shown on the left. On the right is the VIIRS instrument with its nadir doors open. The instrument is mounted on the spacecraft bus.

FIG. 36.

Ratios between SIRCUS-based RSRs and SpMA-based RSRs over the in-band responsivity of each band. Developed by the NPP Instrument Characterization Support Team at NASA’s Goddard Space Flight Center. Reprinted with permission from Barnes et al., Appl. Opt. 54, 10376–10396 (2015). Copyright 2015 The Optical Society.

FIG. 37.

RSR differences for Band M1 between SIRCUS-based RSRs and SpMA-based RSRs over the in-band responsivity of each band. Developed by the NPP Instrument Characterization Support Team at NASA’s Goddard Space Flight Center. Reprinted with permission from Barnes et al., Appl. Opt. 54, 10376–10396 (2015). Copyright 2015 The Optical Society.

FIG. 38.

Detector-to-detector differences in the (a) FWHM bandwidth and (b) band-center wavelength measured using T-SIRCUS and the SpMA. Figures courtesy of David Moyer, The Aerospace Corporation.

FIG. 39.

Total-Band RSRs for band M7. The open squares come from SpMA measurements; the closed circles come from SIRCUS. Channel-to-channel cross talk features are highlighted. Figure courtesy of David Moyer, The Aerospace Corporation.

FIG. 40.

(a) A KeplerCam image of the flat field screen illuminated with 720 nm light taken with the Sloan i′ filter. (b) A plot of the relative spectral responsivity for two pixels in the top-right quadrant of the CCD showing the unique responsivity of each pixel.