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

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

3. 3 Low-Background Infrared Laboratory 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/cm 2 Spectral range 2 - 30  m with filters Uncertainty: currently 3% for Missile Defense Applications. Range of Test Parameters LBIR facilities located at NIST Gaithersburg, MD On-site characterization of Raytheon EKV test chamber Calibration of EKV blackbody in LBIR facility

4. 4 LBIR Infrared Power Standard: Absolute Cryogenic Radiometer (ACR) 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. Thin Walled Copper Black Interior Temperature Sensor Heater Incident IR Photon 2K Heat Sink Thermal Link

5. 5 Broadband Calibration Chamber 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 Broadband Chamber Capabilities (Recommend up to 1 minute) Antechamber to house larger blackbodies (SM3) ACR Test Blackbody Cold Baffle d Aperture 20K Shield 5’ long x 2’ diameter Antechamber for large BBs 5nW - 200  W power range NEP = 50 pW Upgraded Broadband Calibration Chamber

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

7. 7 BCC Backend Configuration for 10 cm Collimator Calibration 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.

8. 8 Spectral Calibration Chamber 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 Spectral Chamber Capabilities (Recommend up to 1 minute) Space Sensor Test Facility Absolute Cryogenic Radiometer Spectral Instrument Blackbody Test Blackbody ACR II Spectral Instrument Detector Holder 20K Shield 5’ long x 2’ diameter 2 -30  m; 1-2% bandpass 1nW - 100  W power range; NEP= 50 pW

9. 9 NIST MDXR 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.

10. 10 Transfer Standard Radiometer (MDXR) 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  m – 16  m spectral range with 0.6 cm -1 resolution. Larger range possible with suitable beam splitters. -Provide Spectral Radiance and Irradiance calibrations.

11. 11 MDXR Operational Modes Fourier Transform Spectrometer Mode KBR Beam Splitter (4  m to 16  m Spectral Range) Spectral Resolution = 1 cm-1 Dynamic Mirror Alignment White Light Reference Step Scan Capability 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 Linear Polarimeter Mode Fixed Polarizer Rotatable Polarizer Wire Grid Polarizers

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

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

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

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

16. 16 BIB Detector Trap Goal: Develop a new calibration standard using high internal quantum efficiency Si:As BIB detectors in a light trapping configuration. 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. 17 Summary 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  m will be delivered to NIST this summer. NEP = 100 fW.

18. 18 Backup Slides

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

20. 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. 21 Electrical-Substitution Radiometer Mode 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/cm 2 with BXR II collection optics –10  W maximum power –2 second response time

22. 22 Electrical-Substitution Radiometer Mode 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. ACR III Spatial Filter Wheel Translation Stage 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%.

23. 23 Filter-Based Radiometer Mode 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/cm 2 and 10 -9 W/cm 2 {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

24. 24 MDXR Filter Set Long-pass cut-off wavelength (  m) Short-pass cut-off wavelength (  m) 4.7985.266 5.7866.254 6.7797.247 7.7908.258 8.7409.208 10.73011.198 12.40612.874. 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 3 o tilt angle to prevent inter-reflections. The filters are fully characterized at 25 Kelvin and at 3 o tilt angle using a FTS. In- situ measurements of the filter transmissions can be made with the Cryo-FT to investigate systematic effects.

25. 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  m square and 3.16 mm square sizes. They have a spectral response over the wavelength range from 2  m to 30  m. 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  m the noise equivalent power of the 1600  m 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. TIADetector Package

26. 26 Fourier Transform Spectrometer Mode Internal Cryogenic Fourier Transform Infrared Spectrometer (Cryo-FT)  KBr Beam Splitter (4  m to 16  m throughput)  Spectral resolution = 1 cm -1 (Scan mirror travel of 1 cm)  Dynamic mirror alignment  White light reference  Step scan capability 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. Porchswing Assembly Beam Splitter Compensator Folding Mirror To BIB Detectors Dynamic Alignment Mirror

27. 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  m and 140 at 10  m Linear Polarization can be measured through the complete filter set

28. 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)