Nd:YAG ceramics for laser applications were elaborated with various residual porosities by reaction-sintering process. The porosity analysis with CLSM and SEM led to the determination of the pore ...volume fraction after sintering. This study revealed that the mean pore size of Nd:YAG ceramics was around 0.7 microm while the residual porosity was ranging between 10(-1)% and 10(-4)%. These pore contents affect the transparency and laser efficiency of ceramics. The analytical model based on the Mie light scattering fairly fits the experimental data. This demonstrates that the porosity in Nd:YAG ceramics should be lower than 10(-4)% to reach single-crystal laser efficiency.
Abstract
Astronomical Light Optical Hybrid Analysis (ALOHA@3.39 μm) is a new instrumental concept designed for high angular resolution astronomical imaging in the L band. The originality of our ...experimental device is to include a frequency conversion process in each arm of the interferometer that frequency shifts the mid-infrared signal to the near-infrared domain. This method relaxes the stringent limitations due to the thermal noise background radiated by the instrument itself. The aim of this paper is to estimate the current sensitivity limit of the instrument and validate the ability to provide calibrated contrasts with a quasi-monochromatic signal. We demonstrate the possibility to measure fringe contrasts greater than 94.5 per cent with a signal-to-noise ratio close to 7. The flux level at the input of each arm of the interferometer is then equal to 100 fw. This would correspond to a zero magnitude star in the L band for a 1 m2 telescope surface and a 3 nm converted spectral bandwidth.
Abstract
In this paper, we propose a multichannel spectral configuration of the Astronomical Light Optical Hybrid Analysis (ALOHA) instrument dedicated to high-resolution imaging. A frequency ...conversion process is implemented in each arm of an interferometer to transfer the astronomical light to a shorter wavelength domain. Exploiting the spectral selectivity of this non-linear optical process, we propose to use a set of independent pump lasers in order to simultaneously study multiple spectral channels. This principle is experimentally demonstrated with a dual-channel configuration as a proof-of-principle.
In this paper, we report on a novel method to control the coherence behavior in a sum frequency generation interferometer powered by two independent pump lines. At the output of the interferometer, ...the two incoherent fringe patterns must be superimposed to maximize the contrast. The first step consists in canceling the differential group delay. The second one uses the phase control on one pump to synchronize the fringe patterns. This innovative method is experimentally demonstrated with a setup involving a 1544 nm signal and two pump lines around 1064 nm leading to a converted signal around 630 nm. It can be easily extended to a greater number of pump lines.
To investigate spectral domain optical coherence tomography (SD-OCT)-detected optic disc margin anatomy in the monkey eye by colocalizing disc photographs to SD-OCT scans acquired from the same eyes.
...The neural canal opening (NCO) was delineated within 40 digital radial sections generated from SD-OCT volumes acquired from 33 normal monkey eyes (15 degrees, 290 x 768 horizontal grid pattern). Each volume was colocalized to its disc photograph by matching the retinal vessels within each photograph to vessel outlines visible within en face SD-OCT images. Border tissue was delineated where it extended internally to the NCO. A clinician (masked to delineated points) marked the disc margin onto each photograph while viewing the relevant stereophotograph pair. Alignment of the clinician-ascribed disc margin to the NCO and border tissue delineation was assessed. The process was repeated in a single myopic human eye.
In 23 eyes, the NCO aligned to the disc margin. In 10 eyes, externally oblique border tissue was detectable in the temporal disc. In these regions of the disc, the termination of border tissue was the disc margin. An exaggerated form of this phenotype was observed in the myopic human eye. In this case, temporal border tissue terminated at the anterior scleral canal opening, which was detected as the disc margin.
The termination of Bruch's membrane, border tissue, and the anterior scleral canal opening may constitute the disc margin within the same eye, depending on the border tissue architecture; this anatomy is consistently visualized by SD-OCT.
Plasma concentrations of dexmedetomidine (D = 0.1 mg/kg), midazolam (M = 2 mg/kg), and butorphanol (B = 0.4 mg/kg) were analyzed by liquid chromatography–mass spectrometry (LC–MS/MS) after their ...simultaneous (DMB) transnasal (TN) administration to healthy rabbits. Time‐dependent changes in sedation and antinociception were evaluated by measuring a sedation score based on rabbit's posture, loss of the righting, palpebral and pedal withdrawal reflexes and by instrumental monitoring of rectal temperature, heart rate, arterial blood pressure, pulse‐oximetry, and capnometry. The peak plasma concentration (Cmax) of each drug was reached within 5 min (Tmax) from DMB‐TN administration along with deep sedation and analgesia. Such effects subsided after 45 min into a moderate sedation and analgesia lasting for additional 15 min. All rabbits awakened spontaneously and uneventfully 90 min after DMB‐TN administration. During the anesthetic procedure, arterial blood pressure markedly decreased and respiratory depression ensued requiring oxygen supplementation. The results of this study show that all three molecules of the DMB combination were absorbed through the TN route, inducing deep sedation and analgesia suitable for minor surgical procedures. Such combination should be used with caution in rabbits bearing cardiovascular or respiratory diseases because of its ability to induce hypotension and respiratory depression.
The Astronomical Light Optical Hybrid Analysis project investigates the combined use of a telescope array interferometer and nonlinear optics to propose a new generation of instruments dedicated to ...high-resolution imaging for infrared astronomy. The nonlinear process of optical frequency conversion transfers the astronomical light to a shorter wavelength domain. Here, we report on the first fringes obtained on the sky with the prototype operated at 1.55 μm in the astronomical H band and implemented on the Center for High Angular Resolution Astronomy telescope array. This seminal result allows us to foresee a future extension to the challenging midinfrared spectral domain.
In the field of high resolution imaging in astronomy, we experimentally demonstrate the spatial-coherence analysis of a blackbody using an up-conversion interferometer in the photon counting regime. ...The infrared radiation of the blackbody is converted to a visible one in both arms of the interferometer thanks to the sum-frequency generation processes achieved in Ti-diffused periodically poled lithium niobate waveguides. The coherence analysis is performed through a dedicated imaging stage which mimics a classical telescope array analyzing an astrophysical source. The validity of these measurements is confirmed by the comparison with spatial-coherence analysis through a reference interferometer working at infrared wavelengths.
We theoretically and experimentally evidence that fiber systems are convective systems since their nonlocal inherent properties, such as the dispersion and Raman effects, break the reflection ...symmetry. Theoretical analysis and numerical simulations carried out for a fiber ring cavity demonstrate that the third-order dispersion term leads to the appearance of convective and absolute instabilities. Their signature is an asymmetry in the output power spectrum. Using this criterion, experimental evidence of convective instabilities is given in a fiber cavity pumped by a pulsed laser.
We report on the implementation of a mid-infrared (MIR) interferometer prototype for furthermore application in the framework of high-resolution imaging in astronomy. This paper demonstrates the ...possibility to extend to the L band our experimental study performed on the up-conversion interferometer in H band. This in-laboratory preliminary experiment allowed us to get the first fringes with the MIR Astronomical Light Optical Hybrid Analysis (ALOHA) @3.39 μm up-conversion interferometer with a bright quasi monochromatic source (HeNe 3.39 μm). A stable contrast greater than 98 per cent has been reached. This opens the possibility to propose an alternative instrument for the demanding domain of high resolution imaging in the MIR domain.
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