David J. Livigni

Heat Transfer Analysis and Modeling of a Cryogenic Laser Radiometer

This study investigates the laser optimized cryogenic radiometer (LOCR) recently acquired by the National Institute of Standards and Technology in Boulder, Colorado, to calibrate laser power meters and detectors. The objectives are to evaluate potentially significant sources of uncertainty in the radiometric measurements and to develop transient models that efficiently and accurately predict the behavior of this radiometer. The analysis suggests that radiation from the Brewster window assembly may cause the total power entering the radiometer to drift more than 130 nW for a room temperature variation of 0.2 K. Steady-state modeling of the LOCR with finite element analysis software indicates a relative inequivalence between optical and electrical heating of 4 × 10 -6 at the 1-mW power level. A new tbermal model has been developed to simplify transient predictions by combining lumped parameter and one-dimensional elements. This model outperforms single-time-constant exponential models and can be expanded to simulate the complete radiometer system.

Reflective attenuator for high-energy laser measurements

A high-energy laser attenuator in the range of 250 mJ (20 ns pulse width, 10 Hz repetition rate, 1064 nm wavelength) is described. The optical elements that constitute the attenuator are mirrors with relatively low reflectance, oriented at a 45 degrees angle of incidence. By combining three pairs of mirrors, the incoming radiation is collinear and has the same polarization orientation as the exit. We present damage testing and polarization-dependent reflectance measurements for 1064 nm laser light at 45 degrees angle of incidence for molybdenum, silicon carbide, and copper mirrors. A six element, 74 times (18 dB) attenuator is presented as an example.

Intramural Comparison of NIST Laser and Optical Fiber Power Calibrations

The responsivity of two optical detectors was determined by the method of direct substitution in four different NIST measurement facilities. The measurements were intended to demonstrate the determination of absolute responsivity as provided by NIST calibration services at laser and optical-communication wavelengths; nominally 633 nm, 850 nm, 1060 nm, 1310 nm, and 1550 nm. The optical detectors have been designated as checks standards for the purpose of routine intramural comparison of our calibration services and to meet requirements of the NIST quality system, based on ISO 17025. The check standards are two optical-trap detectors, one based on silicon and the other on indium gallium arsenide photodiodes. The four measurement services are based on: (1) the laser optimized cryogenic radiometer (LOCR) and free field collimated laser light; (2) the C-series isoperibol calorimeter and free-field collimated laser light; (3) the electrically calibrated pyroelectric radiometer and fiber-coupled laser light; (4) the pyroelectric wedge trap detector, which measures light from a lamp source and monochromator. The results indicate that the responsivity of the check standards, as determined independently using the four services, agree to within the published expanded uncertainty ranging from approximately 0.02 % to 1.24 %.

Comparison of Two Cryogenic Radiometers at NIST

Two cryogenic radiometers from NIST, one from the Optical Technology Division and the other from the Optoelectronics Division, were compared at three visible laser wavelengths. For this comparison, each radiometer calibrated two photodiode trap detectors for spectral responsivity. The calibration values for the two trap detectors agreed within the expanded (k = 2) uncertainties. This paper describes the measurement and results of this comparison.

Optical-Fiber Power Meter Comparison between NIST and PTB

We describe the results of a comparison of reference standards between the National Institute of Standards and Technology (NIST-USA) and Korea Research Institute of Standards and Science (KRISS-R.O. Korea) for optical fiber-based power measurements at wavelengths of 1302 nm and 1546 nm. We compare the laboratories’ reference standards by means of a temperature-controlled optical trap detector. Measurement results showed the largest difference of less than 2.5 parts in 103, which is within the combined standard (k=1) uncertainty for the two laboratories’ reference standards.

Comparison of optical-power meters between the NIST and the PTB

We describe the results of a comparison of optical-power meters undertaken by the National Institute of Standards and Technology (NIST, USA) and the Physikalisch-Technische Bundesanstalt (PTB, Germany) at nominal wavelengths of 1300 nm and 1550 nm. Both laboratories used thermal detectors as reference standards, which were compared using a germanium trap detector as a transfer standard. Measurement results showed differences of less than 1 part in 103, well within the combined uncertainty for both laboratories.

Thermal modeling and analysis of laser calorimeters

We performed detailed thermal analysis and modeling of the C-series laser calorimeters at the National Institute of Standards and Technology for calibrating laser power or energy meters. A finite element method was employed to simulate the space and time dependence of temperature at the calorimeter receiver. The inequivalence hi the temperature response caused by different spatial distributions of the heating power was determined. The inequivalence between electrical power applied to the front and rear portions of the receiver is ^1.7%, and the inequivalence between the electrical and laser heating is estimated to be <0.05%. The computational results are hi good agreement with experiments at the 1% level. The effects of the deposited energy, power duration, and relaxation tune on the calibration factor and cooling constant were investigated. This article provides information for future design improvement on the laser calorimeters. Nomenclature A = area of the cavity aperture, m2 Ac = cross-sectional area of the wire, m2 b = thermopile responsivity, V/K C = heat capacity, J/K

Reduction of short wavelength reflectance of multi-wall carbon nanotubes through ultraviolet laser irradiation

Multi-wall carbon nanotube coatings are used as broadband, low-reflectance absorbers for bolometric applications and for stray light control. They are also used as high emittance blackbody radiators. Irradiation of single wall carbon nanotubes with ultraviolet (UV) laser light has been shown to remove amorphous carbon debris, but there have been few investigations of the interaction of UV light with the more complex physics of multi-wall carbon nanotubes. We present measurements of reflectance and surface morphology before and after exposure of multi-wall carbon nanotube coatings to 248 nm UV laser light. We show that UV exposure reduces the reflectivity at wavelengths below 600 nm and present modeling of the thermal cycling the UV exposure causes at the surface of the carbon nanotubes. This effect can be used to flatten the spectral shape of the reflectivity curve of carbon nanotube absorber coatings used for broadband applications. Finally, we find that the effect of UV exposure depends on the nanotube growth process.Multi-wall carbon nanotube coatings are used as broadband, low-reflectance absorbers for bolometric applications and for stray light control. They are also used as high emittance blackbody radiators. Irradiation of single wall carbon nanotubes with ultraviolet (UV) laser light has been shown to remove amorphous carbon debris, but there have been few investigations of the interaction of UV light with the more complex physics of multi-wall carbon nanotubes. We present measurements of reflectance and surface morphology before and after exposure of multi-wall carbon nanotube coatings to 248 nm UV laser light. We show that UV exposure reduces the reflectivity at wavelengths below 600 nm and present modeling of the thermal cycling the UV exposure causes at the surface of the carbon nanotubes. This effect can be used to flatten the spectral shape of the reflectivity curve of carbon nanotube absorber coatings used for broadband applications. Finally, we find that the effect of UV exposure depends on the nanotube ...

Bilateral Optical Power Meter Comparison Between NIST and CENAM

We describe the results of a comparison of reference standards between the National Institute of Standards and Technology (NIST-USA) and Centro Nacional De Metrología (CENAM-Mexico). Open beam (free field) and optical-fiber-based measurements at wavelengths of 1302 nm and 1546 nm are reported. Both laboratories’ reference standards were compared by means of a temperature-controlled optical trap detector. Measurements showed a largest difference of less than 3.4 parts in 103, which is within the combined expanded (k = 2) uncertainty for the laboratories’ reference standards.

Heat transfer analysis and modeling of a cryogenic laser radiometer

This study investigates the laser optimized cryogenic radiometer (LOCR) recently acquired by the National Institute of Standards and Technology in Boulder, Colorado, to calibrate laser power meters and detectors. The objectives are to evaluate potentially significant sources of uncertainty in the radiometric measurements and to develop transient models that efficiently and accurately predict the behavior of this radiometer. The analysis suggests that radiation from the Brewster window assembly may cause the total power entering the radiometer to drift more than 130 nW for a room temperature variation of 0.2 K. Steady-state modeling of the LOCR with finite element analysis software indicates a relative inequivalence between optical and electrical heating of 4 × 10 -6 at the 1-mW power level. A new tbermal model has been developed to simplify transient predictions by combining lumped parameter and one-dimensional elements. This model outperforms single-time-constant exponential models and can be expanded to simulate the complete radiometer system.