Absolute linearity measurements on HgCdTe detectors in the infrared region

The nonlinearity characteristics of photoconductive and photovoltaic HgCdTe detectors were experimentally investigated in the infrared wavelength region by use of the National Physical Laboratory detector linearity measurement facility. The nonlinearity of photoconductive HgCdTe detectors was shown to be a function of irradiance rather than the total radiant power incident on the detector. Photoconductive HgCdTe detectors supplied by different vendors were shown to have similar linearity characteristics for wavelengths around 10 microm. However, the nonlinearity of response of a photovoltaic HgCdTe detector was shown to be significantly lower than the corresponding value for photoconductive HgCdTe detectors at the same wavelength.     

Parameters of CO2 bands near 3.6 microm

The intensities, widths, and positions of lines of three CO2 bands near 2750 cm-1 have been determined. The results are in general agreement with other measured and estimated values.     

Measurement of the Absolute Frequencies of CO2 Laser Transitions by Multiplication of CO2 Laser Difference Frequencies

It is verified experimentally that frequency differences between CO2 laser lines and the harmonics of these differences can be used as intermediate frequencies to bridge the gap between microwave frequency standards and infrared frequencies. Criteria for the design of a microwave to 30-THz frequency chain are discussed, and experimental details of the measurement of five CO2 isotope laser frequencies to an accuracy of ±2 parts in 109 are presented. The values obtained for the CO2 isotope transitions are 26334.776614 GHz for P(40) of 13C16O2, 27979.469512 GHz for R(6) of 13C18O2, 28665.704581 GHz for P(6) of 12C16O2, 29442.483293 GHz for R(30) of 12C16O2 and 33328.991337 GHz for R(8) of 12C18O2.     

Sky-radiance gradient measurements at narrow bands in the visible

Accurate calibrated measurements of the radiance of the daytime sky were made in narrow bands in the visible portion of the spectrum. These measurements were made over several months and were tabulated in a sun-referenced coordinate system. The radiance as a function of wavelength at angles ranging from 5 to 90 deg was plotted. A best-fit inverse power-law fit shows inversely linear behavior of the radiance versus wavelength near the Sun (5 deg) and a slope approaching inverse fourth power far from the Sun (60 deg). This behavior fits a Mie-scattering interpretation near the Sun and a Rayleigh-scattering interpretation away from the Sun. The results are also compared with LOWTRAN models.     

含氮杂环季铵盐缓蚀剂在CO2-3%NaCl溶液体系中的电化学行为

为控制CO2腐蚀，合成了含氮杂环季铵盐缓蚀剂9912-1，通过电化学实验，研究了该缓蚀剂在CO2-3％NaCl-H2O体系中对碳钢于25℃和90℃下的缓蚀行为。实验结果与挂片失重法测试的结果基本一致。低温下缓蚀效果优于高温下的缓蚀效果。而且该缓蚀剂与硫脲有很好的协同效应。Tafel曲线表明，该缓蚀过程是以控制阴极腐蚀为主，并对其缓蚀机理进行了初步探讨。     

Coherent differential absorption lidar measurements of CO2

A differential absorption lidar has been built to measure CO2 concentration in the atmosphere. The transmitter is a pulsed single-frequency Ho:Tm:YLF laser at a 2.05-microm wavelength. A coherent heterodyne receiver was used to achieve sensitive detection, with the additional capability for wind profiling by a Doppler technique. Signal processing includes an algorithm for power measurement of a heterodyne signal. Results show a precision of the CO2 concentration measurement of 1%-2% 1sigma standard deviation over column lengths ranging from 1.2 to 2.8 km by an average of 1000 pulse pairs. A preliminary assessment of instrument sensitivity was made with an 8-h-long measurement set, along with correlative measurements with an in situ sensor, to determine that a CO2 trend could be detected.     

Absolute measurements of radiation damage in nanometer-thick films

The problem of absolute measurements of radiation damage in films of nanometer thicknesses is addressed. Thin films of DNA (～2-160 nm) are deposited onto glass substrates and irradiated with varying doses of 1.5-keV X-rays under dry N(2) at atmospheric pressure and room temperature. For each different thickness, the damage is assessed by measuring the loss of the supercoiled configuration as a function of incident photon fluence. From the exposure curves, the G-values are deduced, assuming that X-ray photons interacting with DNA deposit all of their energy in the film. The results show that the G-value (i.e. damage per unit of deposited energy) increases with film thickness and reaches a plateau at 30±5 nm. This thickness dependence provides a correction factor to estimate the actual G-value for films with thicknesses <30 nm thickness. Thus, the absolute values of the damage can be compared with that of films of any thickness under different experimental conditions.     

Absolute intensity measurements of the (11(1)0)II <--00(0)0 band of 12C16O2 at 5.2 microm

A nonlinear least-squares fitting procedure has been used to derive absolute intensities for lines in the P, R, and Q branches of the (11(1)0)II <-- 00(0)0 band of 12Cl602 (band center = 1932 cm(-1)) from long-path 0.01-cm(-1) resolution laboratory spectra. The spectral data were recorded at room temperature and low pressure (<10 Torr) with the Fourier transform spectrometer in the McMath solar telescope complex at Kitt Peak National Observatory. The observed line intensities were analyzed to derive the vibrational band intensity and F-factor coefficients. To obtain a good fit to the data, it was necessary to include terms in the expression for the F factor, which account for Coriolis-type and Fermi-type interactions and centrifugal distortion effects.     

Absolute linearity measurements on a PbS detector in the infrared

The nonlinearity characteristics of a commercially available thin-film photoconductive PbS detector were experimentally investigated in the infrared using the National Physical Laboratory detector linearity characterization facility. The deviation from linearity of this detector was shown to be significant even for relatively low values of radiant power incident on the active area of the detector. For example, the linearity factor was approximately 0.8 when 0.6 microW of radiant power at a wavelength of 2.2 microm was illuminating a spot of 1 mm in diameter on the active area of the PbS detector. These figures demonstrate the poor linearity characteristics of this detector and provide a warning to other users of PbS detection systems. The deviation from linearity was shown to be a function of the size of the spot being illuminated on the detector active area, as well as the wavelength of the incident radiation. The deviation from linearity was shown to be a function of irradiance illuminating the detector for irradiance values lower than 1 microW mm(-2).     

Sensitivity of radiometric measurements of the atmospheric CO2 column from space

Anthropogenic emissions of CO(2) over the past century has altered significantly the global carbon cycle. Our understanding of the long-term climatic effects of these emissions would be improved greatly by satellite-based remote sounding of CO(2). We provide an initial analysis of a simple satellite-based filter radiometer tuned to the spectral region around 6300 cm(-1) ( approximately 1.6 mum) to measure the atmospheric column of CO(2) from space. We find that such an instrument has potential and that the sensitivity would be limited by our knowledge of the tropospheric temperature and water-vapor profiles.     

Absolute frequency measurements of lasers in submillimeter and infrared ranges

Conclusion The investigations into lasers constructed in the submillimeter and infrared regions showed satisfactory results for their use in absolute frequency measurements. The fast-response nonlinear elements — W=Si and W=Ni point diodes — have been tested in the multiplier-mixer mode from 337 to 10 exclusively. The frequencies have been measured of the molecular lasers HCN (=337 ), D₂O (=84 ), H₂O (=28 ) and the P(14) CO₂ (=10.53 ) and R(30) (=10.18 ) lines. The measurement error of 5·10^–7 was determined by the indeterminacies of fixing the peak of the laser generation lines. An increase of the measurement accuracy will be achieved by the mutual tying in of the laser frequencies to one another.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 59–61, October, 1976.