Stable Cavity Research Articles

Dynamical stable cavity of side-pumped thin-disk laser with slanted sides

In this article, we use the results of finite-element analysis (FEA) of temperature distribution, deformation, and stress to provide a full three-dimensional simulation of a dynamically stable cavity by propagating wavefront into hot, thermally deformed Yb:YAG/YAG thin-disk laser, using the fast Fourier transform (FFT) split-step beam propagation method (BPM). The wave optics computation therefore delivers realistic results for important features of a laser-like intensity, phase profile, and resonator eigenvalues and higher order-eigenmodes of the laser beam.

LD side-pumped 41 W high beam quality acousto-optical Q-switched single-rod Nd:YAG laser

We report a LD side-pumped high beam quality (M 2 = 1.20 and M 2 = 1.19) acousto-optic (AO) Q-switched single-rod Nd:YAG laser with a TEM00-mode dynamic stable cavity. At the pump power of 600 W, 41 W TEM00-mode 1064 nm laser was achieved with electro-optical conversion efficiency of 7%. The repetition rate and pulse width were 30 kHz and 102 ns, respectively with pulse energy of 1.4 mJ and peak power of 13 kW. Up to 24 W of 532 nm green laser was generated by external frequency doubling, corresponding to 59% optical conversion efficiency.

基于447 nm蓝光激光器基模热稳腔的设计与实验

基于447 nm蓝光激光器基模热稳腔的设计与实验

Electropolymerized Molecularly Imprinted Polymer Films of a Bis-Terthiophene Dendron: Folic Acid Quartz Crystal Microbalance Sensing

A folic acid sensor was prepared via an electropolymerized molecularly imprinted polymer (E-MIP) film of a bis-terthiophene dendron on a quartz crystal microbalance (QCM). The cyclic voltammetry (CV) electrodeposition of the imprinted polymer film was monitored by electrochemical QCM or E-QCM, enabling in situ monitoring and characterization of E-MIP film formation and the viscoelastic behavior of the film. A key component of the E-MIP process is the use of a bifunctional monomer design to precomplex with the template and function as a cross-linker. The complex was electropolymerized and cross-linked by CV to form a polythiophene matrix. Stable cavities were formed that specifically fit the size and shape of the folic acid template. The same substrate surface was used for folic acid sensing. The predicted geometry of the 1:2 folic acid/terthiophene complex was obtained through semiempirical AM1 quantum calculations. The analytical performance, expressed through the figures of merit, of the sensor in aqueous solutions of the analyte was investigated. A relatively good linearity, R(2) = 0.985, was obtained within the concentration range 0-100 μM folic acid. The detection limit was found to be equal to 15.4 μM (6.8 μg). The relative cross selectivity of the folic acid imprinted polymer against the three molecules follows this trend: pteroic acid (= 50%) > caffeine (= 41%) > theophylline (= 6%). The potential and limitations of the E-MIP method were also discussed.

Retrospective and Prospective Study of Singapore Swing Method on Healing of Mastoid Cavity

Chronic suppurative otitis media with cholesteatoma is a common problem. The majority of ENT surgeons find the canal wall down operation to be the safest and simplest means of treating cholesteatoma. The 'Singapore Swing' is a method of promoting healing of mastoid cavity. In this study our main objective was to do Singapore Swing technique in larger number of cases, have long term follow-up and to compare its results with other mastoid operations in which obliteration has not been used. Patients of cholesteatoma were divided into case group and control group. The case group (26 patients) was operated by canal wall down procedure with Singapore Swing obliteration while the control group (62 patients) was operated by same method without any obliteration. Both retrospective and prospective studies were done. Time period of drying of mastoid cavity, numbers of visits to the hospital and hearing status were observed. Subjective satisfaction score of patient (0-10) and Surgeon's satisfaction score (fully satisfied, partially satisfied and not satisfied at all) were measured in both the groups. The time of drying of cavity was <2months in 88.5% of cases, while 27.5% of controls. Mean time of drying of cavity was 46days (1½months) in case group, while it was 89days (3months) in control group. Gain in air conduction was 11-30dB in 33.3% cases and 15.7% of controls. 2 patients in control group had deterioration of 1-10dB in air conduction. Subjective satisfaction score was 8-10 in 42.4% patients in case group, while 25% in control group. Surgeon was fully satisfied in 73% patients of case group and 45% patients of control group. The study suggested that Singapore Swing technique provides a dry, small and stable cavity with better hearing in less time.

Partial Cavity Drag Reduction at High Reynolds Numbers

Air lubrication to reduce hull skin friction is an idea that originated more than a century ago. There are few implementations of this concept, and there are even fewer systematic investigations at high Reynolds numbers. To address this, an experimental investigation was performed at the W. B. Morgan Large Cavitation Channel that examined the drag-reducing effects of a ventilated partial cavity at high Reynolds numbers. The design was accomplished using both linear gravity wave theory and a two-dimensional inviscid numerical model via Fluent. The physical model was a 12 m long flat plate with a plenum on the bottom. The plenum was formed by an abrupt step near the nose and a long sloping reattachment region toward the rear. Air was injected from the aft face of the step to create a cavity approximately 17.8 cm deep. Friction loads, air flow, and cavity pressure were measured over a range of air fluxes and speeds near the cavity design speed of 3.4 m/s. Cavities were shown to be stable with respect to large changes in air flux and slow perturbations in tunnel speed and pressure. Stable cavities were produced that reduced the skin drag by more than 95% over the extent of the cavity, including the cavity closure.

Analysis and synthesis of mirror-lens cavities

Stable and unstable mirror-lens cavities are studied. Relations are obtained for calculating the parameters of a laser beam formed by such cavities with planar and (or) spherical mirrors and one or two lenses. The expressions have no singularities and make it possible to simplify the operations substantially and automate the solution of problems of analysis and synthesis of stable and unstable mirror-lens cavities.

Creation and Maintenance of Cavities Under Horizontal Surfaces in Steady and Gust Flows

An experimental study of air supply to bottom cavities stabilized within a recess under a horizontal surface has been carried out in a specially designed water tunnel. The air supply necessary for creating and maintaining an air cavity in steady and gust flows has been determined over a wide range of speed. Flux-free ventilated cavitation at low flow speeds has been observed. Stable multiwave cavity forms at subcritical values of Froude number were also observed. It was found that the cross-sectional area of the air supply ducting has a substantial effect on the air demand. Air supply scaling laws were deduced and verified with the experimental data obtained.

Dual-Wavelength Single-Longitudinal-Mode Polarization-Maintaining Fiber Laser and Its Application in Microwave Generation

A novel approach for generating high-frequency microwave signals is proposed and experimentally demonstrated. With a pair of wavelength matched fiber Bragg gratings written directly in a polarization-maintaining erbium-doped fiber, a stable short cavity dual-wavelength single-longitudinal-mode (DW-SLM) distributed-Bragg-reflector fiber laser with orthogonal oscillation modes is realized at room temperature. The wavelength spacing between the two lasing modes is 0.374 nm. By heterodyning the two wavelengths of the DW-SLM fiber laser at a photodetector, microwave signal at over 46 GHz is achieved.

High finesse Fabry–Perot cavities in picosecond regime

An R&D activity on high finesse passive Fabry–Perot cavities locked to a mode-locked oscillator is described. A new nonplanar four-mirror cavity geometry is proposed to provide stable laser cavity locking operations. Future developments of this R&D are also given.

Critical cavity in the stretched fluid studied using square-gradient density-functional model with triple-parabolic free energy

The generic square-gradient density-functional model with triple-parabolic free energy is used to study the stability of a cavity introduced into the stretched liquid. The various properties of the critical cavity, which is the largest stable cavity within the liquid, are compared with those of the critical bubble of the homogeneous bubble nucleation. It is found that the size of the critical cavity is always smaller than that of the critical bubble, while the work of formation of the former is always higher than the latter in accordance with the conjectures made by Punnathanam and Corti [J. Chem. Phys. 119, 10224 (2003)] deduced from the Lennard-Jones fluids. Therefore their conjectures about the critical cavity size and the work of formation would be more general and valid even for other types of liquid such as metallic liquid or amorphous. However, the scaling relations they found for the critical cavity in the Lennard-Jones fluid are marginally satisfied only near the spinodal.

Metal cutting by radiation from a CO2 laser with a self-filtering cavity

The possibility of quality cutting by radiation from a CO2 laser with an unstable self-filtering cavity (SFC) is experimentally investigated. The SFC provides the product of the divergence angle by the beam radius close to that for lower modes in a stable cavity (SC), however, at a higher radiation power, which favours faster cutting. In the far-field zone, the SFC beam has a diffraction structure with side maxima, which is usually considered as a negative factor in laser cutting. 25-mm-thick steel slabs have been cut. The comparison of the obtained results with known data on SC lasers shows that the principal characteristics of the cut (the width, edge roughness, specific expenditure of energy) are close in these lasers. A conclusion is made that at the chosen cavity parameters, the specific spatial structure of the SFC laser beam has no significant effect on the cut characteristics.

Coccidioidomycosis and Tuberculosis Coinfection at a Tuberculosis Hospital

Tuberculosis (TB) and coccidioidomycosis can have similar clinical and radiologic presentations but require different treatments. Coinfection with TB and Coccidioides immitis is uncommonly reported and may be underdiagnosed in endemic areas.We performed a retrospective review of the medical records of all patients admitted to a TB referral hospital between 1995 and 2007, and selected all cases of TB and coccidioidomycosis coinfection in patients aged 18 years or older. All admitted patients had a diagnosis of TB and had sputum cultures for both pathogens. We reviewed clinical, laboratory, and radiologic features of the cases, and noted antimicrobial treatments received and outcomes.We identified 9 patients, of whom 7 (78%) were Hispanic. Most patients were male (8/9, 89%), and all were diagnosed with coccidioidomycosis after TB. Three (33%) patients had drug-resistant TB. Six patients had culture-positive TB at the time of the double diagnosis, and 2 patients developed active coccidioidomycosis during their hospital stay. Only 1 had human immunodeficiency virus/acquired immunodeficiency syndrome (HIV-AIDS) (CD4 count, 20 cells/mm). All but 2 patients were treated with antifungal agents. Two patients died, 1 of whom had AIDS. Radiologic studies were unable to distinguish between TB and coccidioidomycosis, except for a patient who developed a new air-fluid level in a previously stable cavity.TB and coccidioidomycosis coinfection should be suspected in coccidioidomycosis-endemic regions among patients with TB who fail to improve clinically or radiologically despite adequate, culture-directed therapy.

A Laser-Diode End-Pumped Nd:YVO4 Slab Laser at 1342nm

A laser-diode end-pumped Nd:YVO4 slab laser with a fat-concave stable cavity at 1342nm is demonstrated. Under the pumping power of 92W, a cw laser of output 17.8W is obtained with the slope efficiency of 25.6%.

Extended Continuous Tuning of a Single-Frequency Diode-Pumped Vertical-External-Cavity Surface-Emitting Laser at 2.3 $\mu$m

We report on single-frequency operation and wide mode-hop-free tuning range of a diode laser-pumped vertical-external-cavity surface-emitting semiconductor laser producing up to 3 mW around 2.3 mum. An optically stable external cavity of only 1.4 mm is formed using a concave dielectric mirror of 2-mm radius. The maximum continuous tuning is about 500 GHz wide, obtained by a synchronized ramp of external cavity length and of the gain medium temperature. We used this tunable source to record a direct absorption spectrum of methane, which is found to match well a simulated spectrum from the HITRAN (high-resolution transmission molecular absorption database http://www.cfa.harvard.edu/hitran) database.

Towards Supercontinuum Cavity Ring-Down Spectroscopy

We report on measurements performed with the broadband variant of Cavity Ring-Down Spectroscopy based on white-light Supercontinuum. Generated by filaments in a quartz block, the Supercontinuum was coupled into the stable optical cavity characterized by a high Q-factor of 104. The ring-down transients of selectively chosen wavelengths were registered sequentially, revealing a difference of their decay times. The demonstrated high precision of decay time measurement (10−4 relative error) opens the perspective for multiwavelength detection of absorbing species with sub ppb (10−9) sensitivity in the unprecedented broad spectral range of Supercontinuum. This is why we intend to call this technique Supercontinuum Cavity Ring-Down Spectroscopy. Finally, we used the Supercontinuum to quantify variations of the wavelength-dependent reflection coefficient of cavity mirrors; as we show, with an absolute accuracy of 10−6.

Cochlear implantation in patients with chronic otitis media: 7 years’ experience in Maastricht

The purpose of this paper is to propose management options for cochlear implantation in chronic otitis media (COM) based on our 7-year experience. Thirteen patients with COM who were candidates for cochlear implantation were identified. COM was divided in an inactive and an active form based on clinical and radiological findings. One major complications and one minor complication were identified in the study group. In case of an active infection or in case of a unstable cavity we advise cochlear implantation as a staged procedure. A single stage procedure is recommended in case of patients with COM presenting with a dry perforation or a stable cavity.

Linear and nonlinear operation regimes of a laser with a transverse inhomogeneity of the cavity length and angular selection

Gaussian modes and pumping threshold values are found for a laser with spherical mirrors and angular selector. It is shown that, compared to the case of plane-parallel mirrors, the threshold overshoot is proportional to the square root of the mirror curvature. In the absence of the Kerr nonlinearity of the medium, exceeding the oscillation threshold of a stable cavity causes steady-state regimes to be established, whereas, for unstable cavities, pulsation regimes arise in a wide range of parameters. Calculations confirm the formation of moving localized structures in a laser with misaligned plane mirrors.

Design of the Advanced LIGO recycling cavities

The current LIGO detectors will undergo an upgrade which is expected to improve their sensitivity and bandwidth significantly. These advanced gravitational-wave detectors will employ stable recycling cavities to better confine their spatial eigenmodes instead of the currently installed marginally stable power recycling cavity. In this letter we describe the general layout of the recycling cavities and give specific values for a first possible design. We also address the issue of mode mismatch due to manufacturing tolerance of optical elements and present a passive compensation scheme based upon optimizing the distances between optical elements.

Stable microwave coaxial cavity plasma system at atmospheric pressure

We present a systematic study of the development of a novel atmospheric microwave plasma system for material processing in the pressure range up to 760 torr and the microwave input power up to 6 kW. Atmospheric microwave plasma was reliably produced and sustained by using a cylindrical resonator with the TM(011) cavity mode. The applicator and the microwave cavity, which is a cylindrical resonator, are carefully designed and optimized with the time dependent finite element Maxwell equation solver. The azimuthal apertures are placed at the maximum magnetic field positions between the cavity and the applicator to maximize the coupling efficiency into the microwave plasma at a resonant frequency of 2.45 GHz. The system consists of a magnetron power supply, a circulator, a directional coupler, a three-stub tuner, a dummy load, a coaxial cavity, and a central cavity. Design and construction of the resonant structures and diagnostics of atmospheric plasma using optical experiments are discussed in various ranges of pressure and microwave input power for different types of gases.