Boson operator elimination method in the laser cooling of solids

We use Bogoliubov's boson variabies elimination method to investigate the laser cooling of solid samples. We derive an exact kinetic equation for the quantum description of the laser cooling of glasses and crystals doped by rare-earth ions and find its stationary solution. We estimate the temperature of a laser-cooled glass doped by three-valence ytterbium

Anti-Stokes femtosecond photon echo in a polymer film

An anti-Stokes model is proposed which explains the room-temperature blue shift of the echo-signal spectrum compared to the spectrum of exciting femtosecond pulses in a polymer film doped with dye molecules. The possibility of realising the anti-Stokes regime of coherent laser cooling of such films is analysed. © 2007 Kvantovaya Elektronika and Turpion Ltd

Quantum stochastic equation for quasi-two-level solid-state laser

A quantum-mechanical description of a radiation-balanced solid-state laser is presented. The impurity ion levels are coupled both by the phonons of the host lattice and by the radiation field. The set of dynamic Heisenberg-Langevine equations for the material system and the phonon operators has been derived. These equations include radiative and nonradiative damping terms and quantum-stochastic forces. This description could be used for investigation of the influence of phonon dynamics on laser stability

Multipulse optical sequences in solid-state photon echo processors

The physical principles of multipulse control of coherent and relaxation processes in solid-state photon echo processors and quantum counters were investigated. The possibility of implementing the technique of narrowing of dipole-broadened spectral lines in optics with the use of multipulse optical sequences (of WAHUHA type) was theoretically considered. © 2007 by Allerton Press, Inc

Anti-Stokes femtosecond photon echo in dye-doped polymer films and the possibility of coherent optical cooling

An anti-Stokes model is proposed to explain the known experimental data on the femtosecond photon echo in dye-doped polymer films at room temperature. The possibility of implementing the anti-Stokes mode of coherent laser cooling of such films is analyzed. © Allerton Press, Inc. 2008

Long Term Outcomes of Pediatric Idiopathic Intermediate Uveitis

Purpose: To describe the course of childhood-onset intermediate uveitis without associated systemic disease, and investigate determinants of outcomes. / Design: A retrospective clinical cohort study. / Setting: Institutional. / Patients: 125 children (221 eyes) (aged 16 years and under). / Main Outcomes and Measures: Outcomes of interest were visual acuity, severity of inflammation, and the occurrence of sight-threatening complications. Variables examined included age and clinical findings at presentation, treatment, and duration of follow-up. Multivariable analysis was undertaken to investigate potential predictors of outcomes. / Results: Median follow-up duration was 57 months. At presentation, best-corrected visual acuity worse than 20/160 was recorded in 11 (4.4%) eyes, and significant vitreous haze (≥2+SUN) in 35 (14%) eyes. Corticosteroid-sparing agents were used in 41 children (33%), with methotrexate most commonly used (27 children, 21.6%). The most frequent complications were raised intraocular pressure n=65 (29.4%), cataract n=41 (18.5%), and cystoid macular edema n=29 (13.1%). At the last visit, 116 (92.8%) patients achieved best-corrected vision of 20/40 or better with quiescent uveitis. The absence of the use of a steroid-sparing immunomodulatory agent was the strongest predictive factor for the development of new macular edema (OR 6.3, 95% CI 2.3 – 16.9, p<0.001) or glaucoma (OR, 6.6, 95% CI 2.5 – 17.9, p<0.001) over the period of observation. / Conclusions: The visual outcomes of childhood-onset idiopathic intermediate uveitis are favorable. The frequency of sight-threatening sequelae of inflammation, which confer a life-long risk of further visual loss, is high. The use of immunomodulatory therapy is associated with a lower risk of developing macular edema and ocular hypertension

Quality assessment of anterior segment OCT images: development and validation of quality criteria

Background: The utility of medical imaging is dependent on image quality. We aimed to develop and validate quality criteria for ocular anterior segment optical coherence tomography (AS-OCT) images. Methods: We undertook a cross-sectional study using AS-OCT images from patients aged 6-16. A novel three-level grading system (good, limited or poor) was developed based on the presence of image artefact (categorised as lid, eyelash, cropping, glare, or movement artefact). Three independent experts graded 2825 images, with agreement assessed using confusion matrices and intraclass correlation coefficients (ICC) for each parameter. Results: There was very good inter-grader IQA agreement assessing image quality with ICC 0.85 (95%CI: 0.84-0.87). The most commonly occurring artefact was eyelash artefact (1008/2825 images, 36%). Graders labelled 621/2825 (22%) images as good and 384 (14%) as poor. There was complete agreement at either end of the confusion matrix with no ‘good’ images labelled as ‘poor’ by other graders, and vice versa. Similarly, there was very good agreement when assessing presence of lash (0.96,0.94-0.98), movement (0.97,0.96-0.99), glare (0.82,0.80-0.84) and cropping (0.90,0.88-0.92). Conclusions: The novel image quality assessment criteria (IQAC) described here have good interobserver agreement overall, and excellent agreement on the differentiation between ‘good’ and ‘poor’ quality images. The large proportion of images graded as ‘limited’ suggests the need for refine this classification, using the specific IQAC features, for which we also report high interobserver agreement. These findings support the future potential for wider clinical and community care implementation of AS-OCT for the diagnosis and monitoring of ocular disease

A new technique for laser cooling with superradiance

We present a new theoretical scheme for laser cooling of rare earth doped solids with optical super-radiance (SR), which is the coherent, sharply directed spontaneous emission of photons by a system of laser excited rare earth ions in the solid state host (glass or crystal). We consider an Yb3+ doped ZBLAN sample pumped at the wavelength 1015 nm with a rectangular pulsed source with a power of ~433W and duration of 10ns. The intensity of the SR is proportional to the square of the number of excited ions. This unique feature of SR permits a dramatic increase in the rate of the cooling process in comparison with the traditional laser cooling of the rare earth doped solids with anti-Stokes spontaneous incoherent radiation (fluorescence). This scheme overcomes the limitation of using only low phonon energy hosts for laser cooling.Comment: 10 pages,6 figure

Femtosecond photon echo in a dye-doped polymer film and the possibility of coherent optical cooling

The signals of primary and stimulated femtosecond photon echoes are investigated in a dye-doped polymer film at room temperature. The homogeneous S 0 → S 1 spectral line width, which is due to the interaction between the impurity molecules and the quasi-local low-frequency modes, is estimated (≈5 × 10 12 Hz). Special attention is paid to the study of spectra of femtosecond echo signals. The short-wave shifts of these spectra, with respect to the spectrum of femtosecond exciting pulses, are observed. These shifts indicate that the anti-Stokes regime of femtosecond pulse emission is realized. Therefore, the coherent regime of laser cooling of solids appears to be possible. The prospects of using of this new cooling regime in the function of a solid-state optical refrigerator are discussed. © Nauka/Interperiodica 2007