Phonon-assisted optical absorption in germanium

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Photometry, colorimetry and radiometry: Issues and applications

Peer reviewed: YesNRC publication: Ye

Near-infrared photoluminescence of orange color standards: then and now

The presence of near-infrared (NIR) photoluminescence has been recently reported in some of the second series of Ceramic Color Standards (CCSII) that are widely used in the calibration and performance evaluation of color measuring instruments. The impact of this photoluminescence effect can cause significant colorimetric errors particularly for broadband measurements using a detector with high spectral responsivity in the NIR region. The magnitude of this effect has been demonstrated for specific color standards and specific instrument systems but has not been unambiguously quantified to allow general predictions or absolute comparisons of different instrument designs or different ceramic tiles. Here we present absolute NIR photoluminescence measurements on three different formulations of the CCSII orange ceramic color standard using the National Research Council of Canada (NRC) Reference Spectrofluorimeter whose spectral range has been recently extended to 1000 nm. The validation for this extended spectral range is shown by comparison of an independent method of instrument calibration using a different combination of physical standards. It is convincingly shown that the two different leaded formulations of this ceramic orange standard issued in 2000 and 2011 have no significant photoluminescence and thus can be used for calibration with any type of spectrophotometer design whereas the unleaded formulation issued in 2011 has significant NIR photoluminescence and should not be used for instrument calibration and validation over an extended range into the NIR for certain spectrophotometers with relatively high throughput in the NIR region, such as a spectrophotometer with polychromatic illumination mode using a xenon source or with monochromatic illumination mode using a Si detector. It is shown that for colorimetric applications, the impact of this NIR fluorescence is only significant for the latter spectrophotometer design with broadband detection with a Si or spectrally flat detector and is negligible with a narrowband PMT detector. These calculated colorimetric results are also consistent with previously estimated colorimetric errors for this type of orange CCSII ceramic tile used to transfer calibration between these two types of detector systems. \ua9 2013 Crown copyright \ua9 National Research Council Canada.Peer reviewed: YesNRC publication: Ye

Preface

Peer reviewed: YesNRC publication: Ye

Photometry, radiometry and \u2018the candela\u2019: evolution in the classical and quantum world

The metrological fields of photometry and radiometry and their associated units are closely linked through the current definition of the base unit of luminous intensity\u2014the candela. These fields are important to a wide range of applications requiring precise and accurate measurements of electromagnetic radiation and, in particular, the amount of radiant energy (light) that is perceived by the human eye. The candela has been one of the base units since the inception of the International System of Units (SI) and is the only base unit that quantifies a fundamental biological process\u2014human vision. This photobiological process spans an enormous dynamic range of light levels from a few-photon interaction involved in triggering the vision mechanism to a level of more than 1015 photons per second that is accommodated by the visual response under bright daylight conditions. This position paper, prepared by members of the Task Group on the SI of the Consultative Committee for Photometry and Radiometry Strategic Planning Working Group (CCPR WG-SP), reviews the evolution of these fields of optical radiation measurements and their consequent impact on definitions and realization of the candela. Over the past several decades, there have been significant developments in sources, detectors, measuring instruments and techniques, that have improved the measurement of photometric and radiometric quantities for classical applications in lighting design, manufacturing and quality control processes involving optical sources, detectors and materials. These improved realizations largely underpin the present (1979) definition of the candela. There is no consensus on whether this radiant-based definition fully satisfies the current and projected needs of the optical radiation community. There is also no consensus on whether a reformulation of the definition of the candela in terms of photon flux will be applicable to the lighting community. However, there have been significant recent advances in radiometry in the development of single-photon sources and single-photon detectors and the growth of associated technologies, such as quantum computing and quantum cryptography. The international acceptance of these new quantum-based technologies requires improved traceability and reliability of measurements at the level of a few photons. This review of the evolution of the candela and the impact of its possible reformulation might lead, in the future, to a reformulation in terms of quantum units (photons). This discussion is timely since redefinitions of four of the other SI base units are being considered now in terms of fundamental constants to provide a more universally realizable quantum-based SI system. This paper also introduces for the first time a fundamental constant for photometry.Les domaines m\ue9trologiques de la photom\ue9trie et de la radiom\ue9trie et les unit\ue9s qui leur sont associ\ue9es sont \ue9troitement li\ue9s par la d\ue9finition actuelle de l\u2019unit\ue9 de mesure de base de l\u2019intensit\ue9 lumineuse : la candela. Ces domaines sont importants pour de nombreuses applications requ\ue9rant des mesures pr\ue9cises et exactes de rayonnement \ue9lectromagn\ue9tique et, en particulier, la quantit\ue9 d\u2019\ue9nergie rayonnante (lumi\ue8re) qui est per\ue7ue par l\u2019\u153il humain. La candela est l\u2019une des unit\ue9s de base qui datent du lancement du syst\ue8me international d\u2019unit\ue9s (SI) et elle est la seule unit\ue9 de base qui quantifie un processus biologique fondamental : la vision humaine. Ce processus photobiologique couvre une \ue9norme plage dynamique de niveaux de luminance allant de l\u2019interaction de quelques photons participant au d\ue9clenchement du m\ue9canisme de la vision, \ue0 un niveau de plus de 1015 photons par seconde qui est adapt\ue9 par la r\ue9ponse visuelle \ue0 la lumi\ue8re du jour. Cet expos\ue9 de position, pr\ue9par\ue9 par les membres du groupe de travail sur le SI du Groupe de travail sur la planification strat\ue9gique du Comit\ue9 consultatif de photom\ue9trie et radiom\ue9trie (CCPR WG-SP), examine l\u2019\ue9volution de ces domaines de mesures de rayonnement optique et leurs r\ue9percussions sur les d\ue9finitions et la r\ue9alisation de la candela. Au cours des derni\ue8res d\ue9cennies, des avanc\ue9es importantes en mati\ue8re de sources, de d\ue9tecteurs, d\u2019appareils et de techniques de mesure ont permis d'am\ue9liorer la mesure photom\ue9trique et radiom\ue9trique quantitative pour des applications classiques dans les processus d\u2019\ue9clairage, de fabrication et de contr\uf4le de la qualit\ue9 qui font appel \ue0 des sources, \ue0 des d\ue9tecteurs et \ue0 des mat\ue9riaux optiques. Ces r\ue9alisations am\ue9lior\ue9es soutiennent grandement la d\ue9finition actuelle (1979) de la candela. Il n\u2019y a aucun consensus sur la question de savoir si cette d\ue9finition fond\ue9e sur le rayonnement r\ue9pond enti\ue8rement aux besoins actuels et projet\ue9s du milieu du rayonnement optique. On ne s\u2019entend pas non plus sur la question de savoir si une reformulation de la d\ue9finition de la candela sur le plan du flux photonique sera applicable au milieu de l\u2019\ue9clairage. Toutefois, on a assist\ue9 r\ue9cemment \ue0 des progr\ue8s importants en radiom\ue9trie, soit dans la mise au point de sources et de d\ue9tecteurs de photons uniques et la croissance des technologies connexes, comme l\u2019informatique quantique et la cryptographie quantique. L\u2019acceptation internationale de ces nouvelles technologies quantiques exige une am\ue9lioration de la tra\ue7abilit\ue9 et de la fiabilit\ue9 des mesures \ue0 l\u2019\ue9chelle de quelques photons. Cette analyse de l\u2019\ue9volution de la candela et des r\ue9percussions de sa reformulation possible pourrait mener ult\ue9rieurement \ue0 une reformulation sur le plan des unit\ue9s quantiques (photons). Cet expos\ue9 vient \ue0 point nomm\ue9, car les d\ue9finitions de quatre autres unit\ue9s de base du SI font actuellement l\u2019objet d\u2019un examen sur le plan des constantes fondamentales pour fournir un SI quantique plus universellement r\ue9alisable. De plus, le pr\ue9sent article pr\ue9sente pour la premi\ue8re fois une constante fondamentale en photom\ue9trie.Peer reviewed: YesNRC publication: Ye

An amorphous-to-crystalline phase transition within thin silicon films grown by ultra-high-vacuum evaporation and its impact on the optical response

A number of thin silicon films are deposited on crystalline silicon, native oxidized crystalline silicon, and optical quality fused quartz substrates through the use of ultra-high-vacuum evaporation at growth temperatures ranging from 98 to 572 \ub0C. An analysis of their grazing incidence X-ray diffraction and Raman spectra indicates that a phase transition, from amorphous-to-crystalline, occurs as the growth temperature is increased. Through a peak decomposition process, applied to the Raman spectroscopy results, the crystalline volume fractions associated with these samples are plotted as a function of the growth temperature for the different substrates considered. It is noted that the samples grown on the crystalline silicon substrates have the lowest crystallanity onset temperature, whereas those grown on the optical quality fused quartz substrates have the highest crystallanity onset temperature; the samples grown on the native oxidized crystalline silicon substrates have a crystallanity onset temperature between these two limits. These resultant dependencies on the growth temperature provide a quantitative means of characterizing the amorphous-to-crystalline phase transition within these thin silicon films. It is noted that the thin silicon film grown on an optical quality fused quartz substrate at 572 \ub0C, possessing an 83% crystalline volume fraction, exhibits an optical absorption spectrum which is quite distinct from that associated with the other thin silicon films. We suggest that this is due to the onset of sufficient long-range order in the film for wave-vector conservation to apply, at least partially. Finally, we use a semi-classical optical absorption analysis to study how this phase transition, from amorphous-to-crystalline, impacts the spectral dependence of the optical absorption coefficient.Peer reviewed: YesNRC publication: Ye

An amorphous-to-crystalline phase transition within thin silicon films grown by ultra-high-vacuum evaporation and its impact on the optical response

A number of thin silicon films are deposited on crystalline silicon, native oxidized crystalline silicon, and optical quality fused quartz substrates through the use of ultra-high-vacuum evaporation at growth temperatures ranging from 98 to 572 \ub0C. An analysis of their grazing incidence X-ray diffraction and Raman spectra indicates that a phase transition, from amorphous-to-crystalline, occurs as the growth temperature is increased. Through a peak decomposition process, applied to the Raman spectroscopy results, the crystalline volume fractions associated with these samples are plotted as a function of the growth temperature for the different substrates considered. It is noted that the samples grown on the crystalline silicon substrates have the lowest crystallanity onset temperature, whereas those grown on the optical quality fused quartz substrates have the highest crystallanity onset temperature; the samples grown on the native oxidized crystalline silicon substrates have a crystallanity onset temperature between these two limits. These resultant dependencies on the growth temperature provide a quantitative means of characterizing the amorphous-to-crystalline phase transition within these thin silicon films. It is noted that the thin silicon film grown on an optical quality fused quartz substrate at 572 \ub0C, possessing an 83% crystalline volume fraction, exhibits an optical absorption spectrum which is quite distinct from that associated with the other thin silicon films. We suggest that this is due to the onset of sufficient long-range order in the film for wave-vector conservation to apply, at least partially. Finally, we use a semi-classical optical absorption analysis to study how this phase transition, from amorphous-to-crystalline, impacts the spectral dependence of the optical absorption coefficient.Peer reviewed: YesNRC publication: Ye

State-of-the art comparability of corrected emission spectra. 2. Field laboratory assessment of calibration performance using spectral fluorescence standards

In the second part of this two-part series on the state-of-the-art comparability of corrected emission spectra, we have extended this assessment to the broader community of fluorescence spectroscopists by involving 12 field laboratories that were randomly selected on the basis of their fluorescence measuring equipment. These laboratories performed a reference material (RM)- based fluorometer calibration with commercially available spectral fluorescence standards following a standard operating procedure that involved routine measurement conditions and the data evaluation software LINKCORR developed and provided by the Federal Institute for Materials Research and Testing (BAM). This instrument-specific emission correction curve was subsequently used for the determination of the corrected emission spectra of three test dyes, X, QS, and Y, revealing an average accuracy of 6.8% for the corrected emission spectra. This compares well with the relative standard uncertainties of 4.2% for physical standard-based spectral corrections demonstrated in the first part of this study (previous paper in this issue) involving an international group of four expert laboratories. The excellent comparability of the measurements of the field laboratories also demonstrates the effectiveness of RM-based correction procedures.Peer reviewed: YesNRC publication: Ye