Hybrid stable-unstable resonators for diffusion-cooled CO(2) slab lasers

We present the numerical and experimental study that we carried out to compare the performances of two hybrid stable-unstable resonators for diffusion-cooled CO(2) slab lasers. The two resonators are designed to fit a 320 mm × 60 mm ×2 mm rf-discharge channel and are both guided in the narrow transverse direction. They differ in the other transverse direction, consisting of a positive- or a negative-branch unstable resonator scheme. The two solutions have been characterized in terms of modal structure, power extraction, stability, and quality of the extracted beam.     

Hollow-waveguide delivery systems for high-power, industrial CO(2) lasers

Hollow-sapphire and metal-dielectric-coated hollow-glass waveguides have been used to deliver CO(2) laser power for industrial laser applications. The transmission, bending loss, and output-beam properties of these waveguides are described. The bore sizes of the hollow-sapphire waveguides were 1070 and 790 μm, and the hollow-glass waveguide had a bore of 700 μm. The waveguides ranged in length from 1.1 to 1.5 m. The sapphire waveguides were bent to 90°, and the hollow-glass waveguides were bent into a full 360° loop. We delivered a maximum of 1.8 kW through the 1070-μm-bore sapphire waveguide and 1.0 kW through the hollow-glass waveguide. All the hollow waveguides incorporated a water jacket to prevent overheating.     

Near-field and far-field characteristics of a MQW waveguide

Definitions of beam half-width and divergence half-angle according to different kinds of methods were investigated. Results of these definitions are given for the fundamental mode and numerical calculation proves that some of them are more appropriate for describing the propagation characteristics of a multiple quantum well (MQW) planar waveguide.     

Solgel alumina coating for hollow waveguide delivery of CO(2) laser radiation

Solgel alumina films were prepared by use of the Yoldas process and were characterized optically and microstructurally. From nitrogen adsorption and electron microscopy, we determined that the material was highly porous, with pores and crystallites of the order of tens of nanometers in size. The infrared transmission and reflectance of the films were measured, and dispersion curves were calculated as a function of firing temperature by extracting the film optical constants from the reflectance and thickness data. The use of this material in a hollow waveguide structure for the delivery of CO(2) laser radiation for surgical applications is discussed. Calculated waveguide losses indicate that solgel-based alumina is a good candidate material for this application.     

Phase locking of CO(2) lasers by the use of diffraction effects

A technique to phase lock CO(2) lasers with spatially separated active media was investigated. Only reflective optics (except for the output coupler) were used, in view of applications of this method in the field of high-power lasers. Phase locking was established when the beams of two resonator branches were made to propagate very close to each other along the so-called coupling path. As a result of diffraction effects both resonators were exchanging energy, establishing a phase-locked operation mode when several locking conditions were fulfilled. A maximum coupling coefficient (the ratio between the diffracted intensity in the second cavity and the intercavity intensity in the first resonator) of 2.6% could be achieved. Because phase locking was highly dependent on the difference between the two resonator lengths, a length control that uses a piezoelectric translator connected to one of the resonator mirrors was used. To detect phase locking, the intensity maximum of the interference pattern of the two laser beams was monitored with a fast detector. By application of a ramp signal to the piezoelectric translator and detection of the peak intensity, the locking range could be measured. Up to a mismatch of the resonator lengths of λ/130, locking could be maintained. The measurements were compared with results of a computer simulation with Huygens-Fresnel integrals to describe diffraction and the one-dimensional Maxwellian equations to calculate supermodes and to analyze their stability. The numerical results showed an excellent agreement with the measured values.     

KY0.58Gd0.22Lu0.17Tm0.03(WO4)2 buried rib waveguide lasers

CW mirrorless laser operation at 1840 nm at room temperature was observed in buried rib waveguides of KY_0.58Gd_0.22Lu_0.17Tm_0.03(WO₄)₂ fabricated by structuring KY(WO₄) substrates by Ar-ion milling and subsequent liquid phase epitaxial growth of the active layer on these substrates. Laser efficiency and laser threshold seems to change with the width of the channels fabricated.     

Performances of OsO(4) stabilized CO(2) lasers as optical frequency standards near 29 THz

In this paper, we report on the metrological capabilities of CO (2)/OsO(4) optical frequency standards operating around 29 THz. Those frequency standards are currently involved in various fields, such as frequency metrology, high resolution spectroscopy, and Rydberg constant measurements. The most impressive features of the standards lies in the 10(-15) level frequency stability allied to a long-term reproducibility (1 yr) of 1.3x10 (-13).     

Polarization-characteristic determination for multichannel CO2 lasers

Polarization characteristics can be measured for engineering CO₂ lasers by means of an instrument consisting of two rigidly fixed insulating plates combined with radiation detectors, which are placed in such a way that the planes of incidence form an angle of 90°. The plates with detectors rotate around the propagation direction in a cyclic fashion. The main flux passes through the plates, and only the reflected paris of the beam are used in the recording. The radiation prom an LN-1,2, NM-I1 laser is partially or completely polarized for about 70–80% of the time of operation. During the rest of the time, the radiation is unpolarized or there is an ongoing change in the orientation of the polarization plane. All the channels are at least partially synchronized in polarization characteristics.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 25–27, July, 1993.     

Thermal effects in a hollow waveguide beam launch for CO(2) laser power delivery

Thermal effects caused by launching conditions in a CO(2) laser beam delivery that uses metallic hollow waveguides is investigated. It is found that front-end clipping is the main cause of thermal loading and generates a steep temperature gradient at the fiber front end while the continuous beam attenuation produces a temperature distribution declining slowly along the waveguide.     

Fabrication of hollow waveguides for CO2 lasers

Germanium-coated metal (silver, gold, and copper) hollow waveguides for CO(2) laser energy delivery have been fabricated by electron-beam evaporation and plating techniques in which an acid-soluble glass mandrel with small surface roughness was used. The transmission characteristics of Ge-coated metal hollow waveguides were studied. Ge-coated Ag hollow waveguides showed smaller loss, 0.2 dBm, for CO(2) laser light than Ge-coated Au and Cu waveguides. The transmission characteristics of Ge-coated Ag hollow waveguides were measured in relation to a core diameter and a bending radius.     

Inverse free electron lasers and laser wakefield acceleration driven by CO2 lasers

The staged electron laser acceleration (STELLA) experiment demonstrated staging between two laser-driven devices, high trapping efficiency of microbunches within the accelerating field and narrow energy spread during laser acceleration. These are important for practical laser-driven accelerators. STELLA used inverse free electron lasers, which were chosen primarily for convenience. Nevertheless, the STELLA approach can be applied to other laser acceleration methods, in particular, laser-driven plasma accelerators. STELLA is now conducting experiments on laser wakefield acceleration (LWFA). Two novel LWFA approaches are being investigated. In the first one, called pseudo-resonant LWFA, a laser pulse enters a low-density plasma where nonlinear laser/plasma interactions cause the laser pulse shape to steepen, thereby creating strong wakefields. A witness e-beam pulse probes the wakefields. The second one, called seeded self-modulated LWFA, involves sending a seed e-beam pulse into the plasma to initiate wakefield formation. These wakefields are amplified by a laser pulse following shortly after the seed pulse. A second e-beam pulse (witness) follows the seed pulse to probe the wakefields. These LWFA experiments will also be the first ones driven by a CO(2) laser beam.     

Nonparaxial analysis of the far-field radiation patterns of double-heterostructure lasers

Previous analytical approximations for the far-field radiation patterns of a double-heterostructure laser have been restricted by TE-mode propagation in slab waveguides. A model that is applicable to both TE- and TM-mode propagation either in a slab waveguide or in a multiple-quantum-well structure is developed. Results of computations agree with the measured irradiance profiles of visible diode lasers of wavelengths from 635 to 670 nm. A process for deriving far-field expressions in terms of the diode-laser parameters listed in data books is suggested. Astigmatic aberration present in the wave front is determined, and the final result is expressed in a form convenient for diffraction analysis of truncated focused (or collimated) diode-laser beams.     

Infrared optical constants for CO2 laser waveguide materials

The infrared optical constants of a number of commercially available glasses and ceramics have been determined by Kramers-Krönig analyses of the reflectance spectra of the materials at near normal incidence. The data derived, the refractive indexn, and extinction coefficientK, have been further analysed to provide an assessment of these materials as hollow waveguides at mid-infrared frequencies. The results demonstrate that the frequency dependence of waveguide transmission is a feature of anomalous dispersion. Furthermore, in the case of beryllia and alumina ceramics, the high transmissions predicted in straight guide at 10.6m can be attributed to the low refractive indices measured for these materials. Some experimental data are presented which substantiate the frequency characteristics of the predicted waveguide transmission.     

Epitaxial growth and properties of (CO3) stabilised BaCuO2 superconducting thin films

We report on the epitaxial growth of BaCuO₂ infinite layer (stabilised with CO₃ groups) thin films by rf magnetron sputtering on (100) SrTiO₃ and (100) LaAlO₃. Excellent (001) films with c4Å are obtained at 540 °C in a sputtering atmosphere of 1–10 mTorr of Ar+O₂ with some addition of CO₂. Off axis x-ray analysis reveal perfect in plane ordering and a tetragonal structure with a=b3.96 Å. For these deposition conditions the resistivity at room temperature is of the order of several cm and exhibits a strong semiconductor-like behaviour. When the deposition temperature is increased to 660 °C, a supercell along the c axis appears with a period of about 8Å. After an in-situ annealing of these films in 7 Torr of oxygen at 500 °C, (300K) falls to 800cm. The resistance versus temperature curve reveals then a metallic behaviour and a superconducting transitions with onsets between 10–40K.     

Multiple pass unstable resonator for an annular gain CO2 laser

The design, construction, and operational characteristics of an optical resonator for an annular gain media are described. The system, developed for laser power extraction investigations in a new type of coaxial discharge geometry, features a folded multipass unstable resonator concept, fabricated from lightweight uncoated diamond-turned aluminum substrates. The resulting cw CO2 device incorporates excitation aspects of the nonself-sustained PIE excitation process in addition to a new magnetic discharge stabilization technique. Laser performance and output beam characteristics are presented.