Excitation dependent losses and temperature increase in various hollow waveguides at 10.6 μm

Theoretical and experimental studies have been made on excitation dependent transmission properties of various hollow waveguides at 10.6 μm. A heat problem of the waveguide has been experimentally treated when high powered CO₂ laser light is launched.     

Low loss smart hollow waveguides with new polymer coating material

A new kind of cyclic olefin polymer COP-E48R has been selected as the dielectric material for a silver hollow glass tube. Owing to its lower extinction coefficient at the wavelength of 10.6 μm, transmission losses for the CO₂ laser light has been reduced significantly in the COP-E48R-coated silver (COP-E48R/Ag) hollow glass waveguide. By properly selecting the film thickness of COP, Er:YAG and CO₂ laser light are shown to be transmitted with low loss simultaneously or independently. Delivery properties of red and green pilot beams were also evaluated.     

Loss reduction of dielectric-coated metallic hollow waveguides for CO2 laser light transmission

A condition for reducing transmission loss of a dielectric-coated metallic hollow waveguide is shown theoretically when the inner metallic surface is not perfect. It is also shown that the transmission loss for CO₂ laser light is 10.6 μm wavelength is able to be estimated from an attenuation spectrum of a short waveguide. By fabricating a ZnSe coated Ag hollow waveguide of short length, we have shown that it has a lower loss than a Ge coated waveguide for CO₂ laser light.     

Efficient diode-pumped Nd:YVO4 continuous-wave laser at 1.34 μm

We report a high-power continuous-wave(cw) diode-pumped efficient 1.34 μm Nd:YVO₄ laser. The laser properties of a low Nd³⁺-doped concentration of the Nd:YVO₄ crystal operating at 1.34 μm formed with a simple plane-concave cavity have been demonstrated. With the incident pump power of 22 W, an output power of 8.24 W was obtained, giving an optical conversion efficiency of 37.5% and slope efficiency of 40%. The thermal effects of cw end-pumped solid-state lasers were studied.     

A low debris laser plasma soft X-ray source

Low debris laser plasma soft X-ray source is of great importance to micro-lithography and microscopy. In this paper, a 1.06 μm YAG laser with 2 J energy, 10 ns duration is employed to irradiate a CO₂ cryogenic target. Soft X-ray spectra from the CO₂ cryogenic target are obtained. Experimental results of debris measurement from both CO₂ cryogenic and Cu targets demonstrate that the light source based on the CO₂ cryogenic target shows great improvement over conventional metal targets in debris reduction.     

Determination of absorption length of CO2 and high power diode laser radiation for ordinary Portland cement and its influence on the depth of melting

The laser beam absorption lengths of CO₂ and a high power diode laser (HPDL) radiation for concrete have been determined. By employing Beer–Lambert’s law the absorption lengths for concrete of CO₂ and a HPDL radiation were 470±22 μm and 177±15 μm, respectively. Indeed, this was borne out somewhat from a cross-sectional analysis of the melt region produced by both lasers which showed melting occurred to a greater depth when the CO₂ laser was used.     

Angular distribution of intensity of reflected radiation investigations of the influence of CO2 laser treatment on optical properties of hydrogenated amorphous silicon

Thin films of hydrogenated amorphous silicon (a-Si:H) were annealed using CO₂ laser radiation (λ=10.6 μm). Changes of optical properties of the treated a-Si:H were investigated using optical transmittance spectroscopy and the angular distribution of intensity of reflected radiation (ADIRR). The CO₂ laser annealing influences the spectral characteristics of the real part of refractive index n and absorption coefficient α of light in a-Si:H. This treatment increases the n and α values as well as the Urbach energy of a-Si:H. Simultaneously it decreases the optical energy gap of this material. The changes of optical parameters at the interfaces of a-Si:H–glass substrate and a-Si:H–air were established.     

Synthesis, characterization and low field emission of CNx nanotubes

Aligned CN_x nanotubes were fabricated by pyrolyzing ethylenediamine on p-type Si(1 1 1) substrates using iron as the catalyst. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrum (XPS) and Raman spectroscopy were used to characterize the CN_x nanotubes. The CN_x nanotubes with the average length of 20 μm and diameters in the range of 50–100 nm have the “bamboo-like” structure and worse crystalline order. The low-field emission measurements of the CN_x nanotubes indicated that 20 μA/cm² current densities were observed at an electric field of 1.4 V/μm and 1.280 mA/cm² were obtained at 2.54 V/μm. The CN_x nanotubes exhibit better field emission properties than the carbon nanotubes and the BCN nanotubes. The emission mechanism of CN_x nanotubes is also discussed.     

CO laser applications in surgery

An investigation of the potential of CO lasers ( = 5–6 μm) in surgery is presented. CO laser radiation appears to have better cutting and coagulating characteristics than the CO₂ laser, which is currently widely used in medicine.     

Quasi-simultaneous ultraviolet and infrared emission from a plasma cathode TEA laser

Quasi-simultaneous laser action in the UV (0.337 μm) and the IR (10.6 μm) was observed from a pulsed laser with a sliding discharge plasma cathode. The laser operates at atmospheric pressure, with a gas mixture of CO₂/N₂/He, at a 0.26/0.50/4.0 lmin⁻¹ flow rate. Output energies of 30 mJ in the IR and 0.35 mJ in the UV were obtained, from a laser discharge volume of 38.0×1.0×2.8 cm³. The optimum gas mixtures have been determined and the temporal behavior of the discharge parameters, the performance characteristics of the laser and the beam spatial distributions were investigated.     

The amplified spontaneous emission in TE CO2 laser with a half-cavity

The new structure with a half-cavity in TE CO₂ laser is described. In this device, a total of nearly 50 lines from transitions in P and R branches of the 9.6 and 10.6 μm bands is observed. The energy, the spot pattern and pulse width of those lines are tested.     

Spectroscopic comparison of aluminium welding plasmas produced by high power CO and CO2 lasers

Welding tests on the aluminium alloy AlMgSi1 (6082) by the use of a high power CO laser with good beam quality show higher penetration depths and better weld seam quality compared with the results obtained with a commercial industrial CO₂ laser. Spectroscopy of the laser-induced welding plasma shows a strong decrease of the intensities of Al(II) lines and no appearance of Al(III) lines in CO laser aluminium welding compared with CO₂ laser welding at the same process parameters. This is a consequence of the shorter 5 to 5.6 μm wavelength of the CO laser leading to reduced beam-plasma interaction.     

A novel CO2 gas analyzer based on IR absorption

Carbon dioxide (CO₂) gas analyzer can be widely used in many fields. A novel CO₂ gas analyzer based on infrared ray (IR) absorption is presented sufficiently in this paper. Applying Lambert–Beer Law, a novel space-double-beam optical structure is established successfully. The optical structure includes an IR source, a gas cell, a bandpass filter with a transmission wavelength at 4.26 μm, another bandpass filter with a transmission wavelength at 3.9 μm, and two IR detectors. Based on Redial Basic Function (RBF) artificial neural network, the measuring model of IR CO₂ analyzer is established with a high accuracy. A dynamic compensation filter is effectively designed to improve the dynamic characteristic of the IR CO₂ analyzer without gas pump. The IR CO₂ analyzer possesses the advantages of high accuracy and mechanical reliability with small volume, lightweight, and low-power consumption. Therefore, it can be used in such relevant fields as environmental protection, processing control, chemical analysis, medical diagnosis, and space environmental and control systems.     

High power, long pulse, CH3I far infra-red laser

A high power, far infra-red laser, pumped by a long pulse high energy CO₂ laser, has been developed to produce 8 μs pulses at 447 μm. The influence of the molecular weight of the far infra-red gas on the absorption of the pump energy is discussed. The results show that the heavy molecules are most convenient for long pulse far infra-red lasers.     

A comparison between characteristics of various laser-based denim fading processes

Our experiments show that the laser fading process has similar, even better results, in some cases, than the conventional technologies of indigo-dyed denim. Using the beams from Nd:YAG laser (1064 nm and its second harmonic 532 nm), CTH:YAG laser (2.09 μm), CO₂ laser (10.6 μm) and various laser beam parameters we found the optimum fluence and power density in order to obtain a similar fading appearance like the one obtained by conventional processes. The purpose of this work was to determine the effectiveness of laser-based technologies and to measure the wear characteristics of the processed textile like colorfastness, strength resistance, tearing strength, and dimensional changes.     

Performance of photon drag and photon drag-optical rectification detectors in the 2 to 33 μm range

Previous studies of the spectral response of p-Ge photon drag and n-Gap photon drag-optical rectification detectors have been extended. Measurements have also been made of the spectral response of p-Si photon drag, p-GaP photon drag-optical rectification and p-GaAs photon drag-optical rectification detectors. The wavelength range of main interest is between 2 and 11 μm, (HF, HCl, HBr, H₂O vapour and CO₂ lasers), but some measurements have also been made at 28 and 33 μm, (H₂O vapour laser).     

Removal of the indigo color by laser beam–denim interaction

Our experiments show that the laser fading process removes efficiently indigo-dye from denim support. We use the beams from Nd : YAG laser (1064 nm and its second harmonic 532 nm) and CO₂ (10.6 μm) lasers. Different laser pulse parameters were used in order to obtain laser power density and fluency to start the ablation process. The purpose of this work is to determine the change of denim diffuse reflectivity spectra after laser irradiation with different wavelength and different power density. The change of diffuse reflectivity coefficient was up to 17% at 450 nm wavelength (from 8% reflectivity for unirradiated denim).     

Novel long-pulse TE CO2 laser excited by pulser–sustainer discharge

A novel long-pulse TE CO₂ laser with UV-preionization is presented. With an active volume of 1.17 l and gas pressure of 30 kPa, the laser can discharge stably with low pulser energy and high sustainer energy. Various long-pulse discharges such as 12, 20 or 25 μs are demonstrated. At discharge pulse width of 23.9 μs, maximum output laser energy of 6.8 J is obtained at an efficiency of 9.0%.     

Quantitative assessment of solid oxide electrochemical doping

Quantitative analysis of metal cation doping by solid oxide electrochemical doping (SOED) has been performed under galvanostatic doping conditions. A M–β″-Al₂O₃ (M=Ag, Na) microelectrode (contact radius: about 10 μm) was used as cation source to attain a homogeneous solid–solid contact between the β″-Al₂O₃ and doping target. In Ag doping into alkali borate glass, the measured dopant amount closely matched the theoretical value. High Faraday efficiencies of above 90% were obtained. This suggests that the dopant amount can be precisely controlled on a micromole scale by the electric charge during electrolysis. On the other hand, current efficiencies of Na doping into Bi₂Sr₂CaCu₂O_y (BSCCO) ceramics depended on the applied constant current. Efficiencies of above 80% were achieved at a constant current of 10 μA (1.6 A cm⁻²). The relatively low efficiencies were explained by the saturation of BSCCO grain boundaries with Na. By contrast, excess Na was detected on the anodic surface of ceramics at a constant current of 100 μA (16 A cm⁻²). In the present study, we demonstrate that SOED enables micromole-scale control over dopant amount.     

Development of surface-textured hydrogenated ZnO:Al thin-films for μc-Si solar cells

This study addresses the optimization of rf magnetron-sputtered hydrogenated ZnO:Al (HAZO) films as front contacts in microcrystalline silicon solar cells. The front contact of a solar cell has to be highly conductive and highly transparent to visible and infrared radiation. Furthermore, it has to scatter the incident light efficiently in order for the light to be effectively trapped in the underlying silicon layers. In this research, HAZO films were rf-magnetron-sputtered on glass substrates from a ceramic (98 wt% ZnO, 2 wt% Al₂O₃) target. Various compositions of AZO films on glass substrates were prepared by changing the H₂/(Ar + H₂) ratio of the sputtering gas. The resulting smooth films exhibited high transparencies (T  85% for visible light including all reflection losses) and excellent electrical properties (ρ = 2.7 × 10⁻⁴ Ω · cm). Depending on their structural properties, these films developed different surface textures upon post-deposition etching using diluted hydrochloric acid. The light-scattering properties of these films could be controlled simply by varying the etching time. Moreover, the electrical properties of the films were not affected by the etching process. Therefore, within certain limits, it is possible to optimize the electro-optical and light-scattering properties separately. The microcrystalline silicon (μc-Si:H)-based p–i–n solar cells prepared using these new texture-etched AZO:H substrates showed high quantum efficiencies in the long wavelength range, thereby demonstrating effective light trapping. Using the optimum AZO:H thin-film textured surface, we achieved a p–i–n μc-Si solar cell efficiency of 7.78%.