Identification of Optical Parameters for Determination of Radiance

The ‘brightness’ of coherent beams such as lasers is known as ‘radiance’ in radiometric terms. It is a concept which is rarely taken into account in laser material processing, laser system design, and for the characterization of laser beams. The typical beam parameters such as: laser power; spot size; intensity; wavelength; beam divergence and the beam propagation factor - M2, combined together are factors which determine the ‘radiance’ of lasers or energy beams in general. The concept of ‘brightness’ (‘radiance’ in particular), and how the laser beam parameters contribute to affect ‘radiance’, has not so far been reported in previous literature. Thus, we have investigated the theoretical ‘radiance’ for each parameter in relation to one another. In addition, a rather suitable empirical equation to determine the ‘radiance’ was also introduced herein, since, the existing equation for calculating ‘brightness’ do not employ the total power intensity of the beam. Based on this, we consider ‘power density’ rather than the ‘output power’ for determining radiance of a selected 1.064 μm wavelength Nd:YAG laser for a set laser processing parameter window. The analytical investigation firstly concluded that the inclusion of ‘power density’ into the equation takes in account of ‘spot size’ and ‘laser power’ to cover all laser beam parameters. Secondly, the results have shown wavelength to be the most contributory parameter to influence the radiance value followed by power density, M2, laser power and lastly the spot size of the laser beam. This was for a set-condition applied, but is generically applicable to different conditions and parameters, whereby, the same tendency would occur. This novel concept of brightness (radiance), of light sources such as a laser beam is not just useful for process control during laser material processing, but could prove to be a very effective concept for laser beam characterization, and in laser system design for enhancing the ‘brightness’ or ‘radiance’ of lasers. Also not just lasers but, the concept could be applicable for other energy beams in general.Publisher Statement: The final publication is available at Springer via http://dx.doi.org/10.1007/s12596-014-0219-

ÉVOLUTION DES RECHERCHES DANS LE DOMAINE DES LASERS A GAZ

Cet exposé a pour but de définir l'évolution des recherches dans le domaine des lasers à gaz au cours des cinq dernières années et d'essayer de prévoir la progression des travaux au cours des années à venir. On indiquera que les principaux objectifs de cette recherche sont, d'une part, l'obtention d'une énergie importante en un temps court en vue des études de démonstration de la faisabilité de la fusion thermonucléaire par laser, d'autre part, l'étude des phénomènes permettant de réaliser des sources délivrant une grande puissance moyenne. On remarquera que, pour atteindre ces objectifs, il est nécessaire de convertir les énergies électrique ou chimique en énergie laser dans des milieux gazeux denses. On expliquera pourquoi l'utilisation de milieux denses comporte d'importantes difficultés et on décrira comment, en particulier à Marcoussis, on a pu les dominer. Les lois des phénomènes physiques qui commandent le fonctionnement des dispositifs qui ont été réalisés sont maintenant suffisamment bien comprises pour permettre de prévoir l'élaboration de nouvelles générations de lasers dans la plage ultraviolette et peut-être dans celle des rayons X.In this article our intention is to assess the progress of research in the field of gas lasers in the last five years and to offer a tentative prediction of what the evolution might be in the years to come. The main objectives of work in this area are, first, obtaining the high laser energies in short time durations needed for the feasibility studies of laser induced thermonuclear fusion, second, investigating the physical principles that can be used to make laser sources capable of delivering high average powers. We note that, in order to reach both objectives, one has to convert electrical or chemical energy into laser energy, using dense gaseous media. We next explain the very important difficulties encountered in working with dense gases for that purpose, and we shall describe how, especially at "laboratoires de Marcoussis", one has been able to master them. The physical phenomena that control the operation of presently existing laser devices are now sufficiently well understood, so that it is possible to predict thàt new generations of lasers could be designed in the future, operating in the UV or even possibly in the X ray region of the spectrum

Influence d'Alfred Kastler sur les applications des sciences de l'optique

Le Professeur Kastler entretenait des relations amicales avec les chercheurs de l'industrie française qui trouvaient toujours auprès de lui et de son groupe des conseils précieux et de cordiaux encouragements. Grâce à l'influence du Professeur Kastler les équipes françaises ont remporté de grands succès scientifiques et économiques dans le domaine des applications des ondes cohérentes

Supplementary Material for: Psychosocial Impact of Dysarthria: The Patient-Reported Outcome as Part of the Clinical Management

Background: Dysarthria in neurological disorders can have psychosocial consequences. The dysarthric speaker’s perspective towards the disorder’s psychosocial impact is essential in its global assessment and management. For such purposes, assessment tools such as the Dysarthria Impact Profile (DIP) are indispensable. Objective: We aimed to confirm the relevance of using the DIP to quantify the psychosocial consequences of dysarthria in neurological diseases. Methods: We studied 120 participants, 15 healthy controls and 105 patients with different kinds of dysarthria induced by several neurological disorders (Parkinson’s disease [PD], Huntington’s disease, dystonia, cerebellar ataxia, progressive supranuclear palsy [PSP], multiple system atrophy, lateral amyotrophic sclerosis). All participants underwent a cognitive evaluation and a speech intelligibility assessment and completed three self-reported questionnaires: the 36-Item Short Form Health Survey, the Voice Handicap Index (VHI), and the DIP. Results: The psychometric properties of the DIP were confirmed, including internal consistency (α = 0.93), concurrent validity (correlation with the VHI: r = –0.77), and discriminant validity (accuracy = 0.93). Psychosocial impact of dysarthria was revealed by the DIP for all patients. Intelligibility loss was found strongly correlated with the psychosocial impact of dysarthria: for a similar level of intelligibility impairment, the DIP total score was similar regardless of the pathological group. However, our findings suggest that the psychosocial impact measured by the DIP could be partially independent from the severity of dysarthria (indirectly addressed here via speech intelligibility): the DIP was able to detect patients without any intelligibility impairment, but with a psychosocial impact. Conclusions: All patients reported a communication complaint, attested by the DIP scores, despite the fact that not all patients, notably PD, ataxic, and PSP patients, had an intelligibility deficit. The DIP should be used in clinical practice to contribute to a holistic evaluation and management of functional communication in patients with dysarthria