NIST LBIR Capabilities for Absolute Radiometric Calibrations

1. Dr. Raju Datla NIST Optical Technology Division Gaithersburg, MD 20899 PIs: Dr. Adriaan Carter & Dr. Timothy Jung NIST LBIR Capabilities for Absolute Radiometric Calibrations

2. Absolute Cryogenic radiometer (ACR) - Absolute Standard for LBIR Measurements Blackbody Calibrations MDXR – LBIR Transfer Standard Radiometer Capabilities and Possibilities BIB Trap detectors Summary Outline

3. Low-Background Infrared Laboratory Calibration of EKV blackbody in LBIR facility On-site characterization of Raytheon EKV test chamber Range of Test Parameters LBIR facilities located at NIST Gaithersburg, MD • Blackbody calibrations • 1 nW – 100 W power range • Uncertainty (Currently 1 sigma 100mK) • ( Future 30 mK for CLARREO) • Currently On-site measurements with portable cryogenic radiometer - BXR • Irradiance levels: 10-15 to 10-9 watts/cm2 • Spectral range 2 - 30 m with filters • Uncertainty: currently3% for Missile Defense Applications.

4. The Absolute Cryogenic Radiometer (ACR) traps 99.995 % of all photons entering its aperture and converts them into thermal power. The changes in thermal power are converted into changes in electrical power, thus tying optical power to the electrical power standard. This can be done at LBIR with an absolute accuracy of 0.02% at the entrance of the ACR defining aperture. ACRs are very accurate, but typically are very slow and the very wide range of spectral sensitivity can make them difficult to use for spectral work. LBIR Infrared Power Standard:Absolute Cryogenic Radiometer (ACR) Thermal Link Thin Walled Copper Black Interior Heater 2K Heat Sink Incident IR Photon Temperature Sensor

5. 20K Shield Cold Baffle Aperture Test Blackbody d ACR (Recommend up to 1 minute) Broadband Calibration Chamber 5nW - 200W power range NEP = 50 pW 5’ long x 2’ diameter Antechamber for large BBs Upgraded Broadband Calibration Chamber Broadband Chamber Capabilities • Broadband Calibration of Blackbodies and Radiometers • (SDL, EKV, SM3, 7V and 10V etc. ) Blackbodies for Missile Defense Agency Contractors • BXR radiometer • Antechamber to accommodate large blackbodies Antechamber to house larger blackbodies (SM3)

6. 1.83 m focal length primary. 1.1 mrad to 27 mrad collimation. 2-axis pointing mirror. Chopper is placed between the blackbody and the aperture wheel for AC lock-in detection. 10 cm Collimator (side view)

7. A 7 cm aperture (not shown here) is positioned to capture the same portion of the beam that the 7 cm BXR aperture captures. The mirror is then moved to focus the irradiance into the ACR. The irradiance from the 10CC passes through the cryostat. BCC Backend Configuration for 10 cm Collimator Calibration

8. 20K Shield Detector Holder Spectral Instrument Test Blackbody ACR II (Recommend up to 1 minute) Spectral Calibration Chamber Absolute Cryogenic Radiometer Spectral Instrument 1nW - 100W power range; NEP= 50 pW 5’ long x 2’ diameter 2 -30m; 1-2% bandpass Blackbody Spectral Chamber Capabilities • Spectral Calibration of Detectors, Blackbodies and Optical Materials • Spectral Instrument covers 2 to 30 micrometers at 2% resolution. • Presently Reconfigured for Broadband Blackbody Calibrations (EKV, 7V) • Spectral Instrument Removed Space Sensor Test Facility

9. The Low-Background Infrared (LBIR) calibration facility at NIST is developing a transfer radiometer offering a variety of infrared source evaluation modes. The instrument is capable of measuring the absolute radiance of Lambertian sources, the absolute irradiance of collimated sources, the spectral distribution of those sources, and their linear polarization. The MDXR is a liquid-helium cooled radiometer that includes a collimated blackbody source and two types of detectors, an electrical substitution radiometer and As-doped Si Blocked Impurity Band (BIB) detectors. Its collection optics include a 7 cm defining input aperture and an off-axis primary parabolic mirror with an eight-position spatial filter wheel at its focus. Apertures placed in the spatial filter wheel reduce background radiation and define the angular acceptance of the radiometer. A confocal, off-axis, secondary parabolic mirror recollimates the input beam into a smaller diameter beam into which a rotating polarizer, filters and a cryogenic Fourier transform spectrometer (Cryo -FT) can be positioned. Finally, a tertiary off-axis mirror focuses light onto any one of seven different BIB detectors mounted on a three-axis translation stage. All the radiometer optical elements are mounted on a two-axis tilt stage allowing alignment with the optical axis of a source chamber. Although the critical components of the transfer radiometer are designed to operate at temperatures below 15 K, the MDXR is capable of providing calibrations for both ambient and low-temperature source chambers. An integral, liquid-helium cooled sliding baffle tube can be used to mate the shrouds of the radiometer with those of low-temperature source chambers. Three primary source evaluation modes will be available with the instrument. NIST MDXR

10. Key Attributes Transportable to User Facility Equipped with NIST Traceable Standards Cryogenic Instrument but Adaptable to Ambient Operation Key Instruments Resident ACR will provide multiple functions. Improve the accuracy of transfer calibration activities. Provide radiance calibration capability to monochromatic large area sources. Cryogenic Fourier Transform Spectrometer. Current KBr beam splitter provides 4 mm – 16 mm spectral range with 0.6 cm-1 resolution. Larger range possible with suitable beam splitters. Provide Spectral Radiance and Irradiance calibrations. Transfer Standard Radiometer (MDXR)

11. MDXR Operational Modes • ACR (Absolute Cryogenic Radiometer) Mode • Internal electrical substitution radiometer • Radiance Measurements • High Power version for ambient temperatures • NEP = 50 pW • Filter-Based Radiometer Mode • Irradiance Measurements • Radiance Measurements • Fourier Transform Spectrometer Mode • KBR Beam Splitter (4 mm to 16 mm Spectral Range) • Spectral Resolution = 1 cm-1 • Dynamic Mirror Alignment • White Light Reference • Step Scan Capability • Linear Polarimeter Mode • Fixed Polarizer • Rotatable Polarizer • Wire Grid Polarizers

12. MDXR Chamber Liquid He Cryotank for BIB Detectors and ACR LN2 Reservoir LN2 Cryotank Liquid He Cooled Sliding Baffle Tube

13. MDXR Internal Collimator with Resident Calibrated Blackbody Ellipsoid Spatial Filter Source Aperture 300 K Blackbody Primary Paraboloid 7 cm Defining Aperture Paraboloid

14. Filter-Based Radiometer Mode Tertiary Paraboloid BIB Detectors Filter Wheels Translating Periscope Incoming Beam Cryo-FT Location 3-Axis Stage Secondary Paraboloid

15. MDXR Calibration Chain NIST High-Accuracy Cryogenic Radiometer (POWR) Using Calibrated Si Trap Detector Intercomparison NIST LBIR Absolute Cryogenic Radiometer (ACR) Using 7 cm Defining Aperture And Parabolic Mirror NIST 10 cm Collimator (10CC) Using Absolute Filter, Mirror, and Aperture Measurements NIST Transfer Radiometer (MDXR) Water Bath BB MDXR ACR III Using NIST Diffraction Modeling User Facility - Radiance and Irradiance Calibrations

16. Goal: Develop a new calibration standard using high internal quantum efficiency Si:As BIB detectors in a light trapping configuration. BIB Detector Trap • Performance expectations: - NEP = 100 fW. Calibration with ACRs planned. - Faster than 0.0001 second response time (10 KHz). - No back reflection issues. • Detector delivery expected July 20, 2008.

17. LBIR ACRs provide radiance temperature measurements for blackbodies having emissivity close to unity. Current uncertainty for ambient BB – (1σ) 100mK, Future (1σ) 30 mK. Transportable transfer radiometer (MDXR) on horizon Radiance and irradiance calibrations with spectral possibilities. Highly sensitive, linear and flat response BIB trap detectors that cover the range 2 to 30 mm will be delivered to NIST this summer. NEP = 100 fW. Summary

18. Backup Slides

19. MDXR Chamber Outer titanium chamber removed to reveal liquid nitrogen cryoshroud

20. MDXR Internal Source Assembly An internal collimated blackbody source will be included in the BXR II. The blackbody will be operated at 300 Kelvin and will be mounted outside the liquid helium cooled cryoshroud. Confocal ellipsoid and parabolic mirrors are used to create a beam with an angular divergence of less than 500 microradian full-cone. The 1 mm source aperture, mirrors and spatial filter are mounted on a rotation stage allowing the beam to be rotated into the 7 cm entrance aperture of the BXR II. The internal collimated source will serve several functions. As a stable reference source the beam will be used to verify the stability of the MDXR components after shipping, as well as before and after a user source chamber evaluation. As a beam with a known spectral distribution, it will be used as a reference for the Cryo-FT and for measuring its throughput in step mode.

21. Internal electrical substitution radiometer for absolute radiance and irradiance measurements of both broadband and narrow band sources High-power version for sources at ambient temperatures 50 pW noise floor, can measure beam irradiances as low as 0.1 pW/cm2 with BXR II collection optics 10 mW maximum power 2 second response time Electrical-Substitution Radiometer Mode

22. Electrical-Substitution Radiometer Mode The Absolute Cryogenic electrical-substitution Radiometer (ACR III) is operated at temperatures below 4 Kelvin by cooling it with a vacuum pumped liquid helium cryotank. Calibration and equivalence measurements of the ACR III are performed with a stabilized HeNe laser and a Si trap detector that is calibrated with the national standard High Accuracy Cryogenic Radiometer (POWR), Intercomparison between the response of the POWR and ACR III shows agreement better than 99.9%. • The electrical substitution radiometer is mounted on a translation stage to bring its black-painted cavity into the source beam just beyond the spatial filter wheel. Therefore the only optical elements before the radiometer are the primary mirror and a spatial filter aperture. The spatial filter wheel has several measured apertures (0.14, 0.20, 0.28, 0.50, 1.00, and 1.50 mm diameters) that are either overfilled for radiance measurements or underfilled (to reduce diffraction losses) for irradiance measurements. The solid angle accepted in a radiance measurement is approximately defined by the aperture diameter and primary mirror focal length. Translation Stage ACR III Spatial Filter Wheel

23. As-doped Si BIB detectors and they configured in a trap versin are the primary detectors Irradiance measurements Required user source collimation O1 mrad full cone Measures collimated beams with irradiance levels between 10-15 W/cm2 and 10-9 W/cm2 {BIBs NEP=100 femto watts) MDXR is calibrated for these measurements using a calibrated collimator, the NIST 10 cm Collimator (10CC) Radiance measurements Can use 0.14, 0.20, and 0.28 mm diameter spatial filter apertures corresponding to 0.38, 0.54 and 0.76 mrad full cone acceptance angles MDXR is calibrated for these measurements using a calibrated, large area blackbody source, the NIST LBIR Waterbath blackbody Filter-Based Radiometer Mode

24. MDXR Filter Set Long-pass and short-pass filters are placed in series to define several 300 nm wide bands. Four eight-position filter wheels hold the filters at a 3o tilt angle to prevent inter-reflections. The filters are fully characterized at 25 Kelvin and at 3o tilt angle using a FTS. In-situ measurements of the filter transmissions can be made with the Cryo-FT to investigate systematic effects.

25. MDXR BIB Detectors The MDXR will include seven Arsenic-doped Silicon BIB Detectors. The detector package includes 50, 100, 200, 400, 800 and 1600 mm square and 3.16 mm square sizes. They have a spectral response over the wavelength range from 2 mm to 30 mm. Each will be used with an integral trans-impedance amplifier whose feedback resistors are operated at the detector temperature of 11 Kelvin. At a wavelength of 10 mm the noise equivalent power of the 1600 mm square detector and amplifier is less than 1 fW. The detectors are mounted on a 3-axis stage allowing for size selection and the spatial imaging of the source and the 7 cm entrance aperture. In addition, the source can be brought into and out of focus to assess detector saturation effects. TIA Detector Package

26. Fourier Transform Spectrometer Mode • Internal Cryogenic Fourier Transform Infrared Spectrometer (Cryo-FT) • KBr Beam Splitter (4mm to 16mm throughput) • Spectral resolution = 1 cm-1 (Scan mirror travel of 1 cm) • Dynamic mirror alignment • White light reference • Step scan capability Compensator Porchswing Assembly Beam Splitter The Cryo-FT can be brought into the path of the recollimated input beam by translating the MDXR periscope. Its exit beam passes through the filter wheels and the interferogram is measured by one of the BIB detectors. The 3 dB roll-off of the BIB amplifier is in excess of 35 kHz. Therefore, at a scan rate of 1 second, 16,384 and 32,768 samples can be collected over the 1 cm travel preventing aliasing effects down to at least 2 mm. Dynamic Alignment Mirror Folding Mirror To BIB Detectors

27. Linear Polarimeter Mode • Rotatable polarizer placed after Mersenne telescope • Fixed polarizer placed in filter wheel to define laboratory orientation • Wire Grid Polarizers on ZnSe substrates • Contrast ratios of 135 at 5 mm and 140 at 10 mm • Linear Polarization can be measured through the complete filter set

28. MDXR Status • Modeling Completed (2005) • Capabilities will become available in three phases corresponding to the three primary source evaluation modes • Electrical-substitution radiometer mode (Summer 2008) • Filter-based radiometer mode (Fall 2008) • Fourier transform radiometer mode (Winter 2008)