Passive alignment stability and auto-alignment of multipass amplifiers based on Fourier transforms.

This study investigates the stability to tilts (misalignments) of Fourier-based multipass amplifiers, i.e., amplifiers where a Fourier transform is used to transport the beam from pass to pass. Here, the stability properties of these amplifiers to misalignments (tilts) of their optical components have been investigated. For this purpose, a method to quantify the sensitivity to tilts based on the amplifier small-signal gain has been elaborated and compared with measurements. To improve tilt stability by more than an order of magnitude, a simple auto-alignment system has been proposed and tested. This study, combined with other investigations devoted to the stability of the output beam to variations in aperture and thermal lens effects of the active medium, qualifies the Fourier-based amplifier for the high-energy and high-power sectors.

Multipass amplifiers with self-compensation of the thermal lens.

We present an architecture for a multipass amplifier based on a succession of optical Fourier transforms and short propagations that shows a superior stability for variations of the thermal lens compared to state-of-the-art 4f-based amplifiers. We found that the proposed multipass amplifier is robust to variations of the active medium dioptric power. The superiority of the proposed architecture is demonstrated by analyzing the variations of the size and divergence of the output beam in the form of a Taylor expansion around the design value for variations of the thermal lens in the active medium. The dependence of the output beam divergence and size is investigated also for variations of the number of passes, for aperture effects in the active medium, and as a function of the size of the beam on the active medium. This architecture makes efficient use of the transverse beam filtering inherent in the active medium to deliver a beam with excellent quality (TEM00).

An Unusual Cause of Increasing Excessive Daytime Sleepiness in a CPAP-treated Obstructive Sleep Apnea Patient.

The onset of narcolepsy type 1 (NT1) occurs after 50 years of age in less than 2% of the cases. In older adults, the diagnosis is often delayed due to the presence of neurological degenerative and inflammatory comorbidities and overlapping sleep disorders. We report the case of a 63-year-old man with a 5-year history of excessive daytime sleepiness (EDS) and a 2-year diagnosis of obstructive sleep apnea syndrome (OSAS), which. OSAS was confirmed by respiratory polygraphy that showed an apnea-hypopnea index (AHI) of 71 events/hour of sleep associated with significant nocturnal hypoxemia (lowest oxygen saturation: 53%), which lead to the initiation of continuous positive airway pressure (CPAP) treatment. Cognitive complaints, unexplained spells of dizziness, and lack of improvement in EDS with CPAP led to further diagnostic investigation of infectious, inflammatory, and neurodegenerative disorders. Low hypocretin levels in the cerebrospinal fluid (CSF) confirmed the diagnosis of NT1, and the patient's symptoms improved with the treatment with pitolisant. Though exceptional in older adults, NT1 should be suspected in the presence of atypical EDS with neurological complaints, unexplained dizzy spells, or OSAS that resists the CPAP treatment. Low levels of hypocretin in the CSF are highly specific and rule out other neurological and sleep disorders.

Cytotoxic lesions of the corpus callosum during the course of ketotic hyperglycemia revealing type I diabetes: A case report.

Cytotoxic lesions of the corpus callosum are lesions secondary to different medical conditions. Radiologically, lesions are identified on magnetic resonance imaging as a hyperintense signal on diffusion-weighted imaging and decreased apparent diffusion coefficient values of the splenium of corpus callosum. Signal changes are reversible in almost totality of the cases. Previous cases of cytotoxic lesions of the corpus callosums have been associated with several metabolic disturbances, but ketotic hyperglycemia has never been reported. We here discussed the case of 28-year-old patient with complex visual hallucinations presenting with cytotoxic lesions of the corpus callosums and type I diabetes. Treatment of hyperglycemia was followed by full clinical recovery and complete regression of the radiological abnormalities at 3-month follow-up. Elevated levels of circulating pro-inflammatory mediators associated with ketotic hyperglycemia in type I diabetes support an implication of cytokines in the pathophysiology of the cytotoxic lesions of the corpus callosums.