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.     

Variational analysis of Er:Ti:LiNbO3 waveguide lasers based on Gaussian/two-half Gaussian mode field distribution

Starting with two dimensional, scalar wave equation, a variational equation was established for the fundamental TE and TM modes guided in Ti:LiNbO₃ waveguides on the basis of assuming a symmetric Gaussian mode field function in the width direction and two-half Gaussian trial functions in the depth direction. The controllable waveguide fabrication parameters, including channel width, diffusion temperature, initial Ti-strip thickness and diffusion time, dependent of fundamental mode size, effective pump area, coupling efficiency between pump and laser modes, and the coupling loss between a Ti:LiNbO₃ waveguide and a fiber were numerically calculated for Z-cut Er:Ti:LiNbO₃ channel waveguide lasers at three possible emission wavelengths 1532,1563 and 1576 nm and two possible pump wavelengths 1480 and 980 nm. The calculated results were compared with those of Gaussian/Hermite–Gaussian mode field distribution in detail.     

Waveguide CO2 lasers on sequence-band transitions

Two waveguide CO₂ lasers, a quartz waveguide and an alumina waveguide, have been studied on the 00°2–[10°l,02°1]_I,II sequence bands. The use of an intra-cavity hot CO₂ cell, which is a part of the waveguide, suppresses the regular-band transitions. The quartz waveguide laser has a total of 58 lines lasing on both the 9.4 µm and 10.4 µ,m sequence bands. The alumina waveguide laser has 36 lines lasing on the 10.4 µm sequence band and twice the output power of the quartz waveguide laser, whereas lasing on the 9.4 µm sequence band is difficult. The lasers can be operated on the selected single line without line jumping problem. The frequency tuning range of the strong lines is limited by the free spectral range of the cavity.     

Radio frequency excited waveguide CO2 lasers on sequence-band transitions

2 lasers based on either a quartz or an alumina waveguide were studied on the 00°2 - [10°1,02°1]_I,II sequence bands. A compact multisegment RF excitation with capacitive coupling was used for pumping the gain section of the laser waveguide. The use of a separate intracavity hot CO₂ waveguide suppresses the regular-band transitions. The quartz waveguide laser has a total of 62 lines lasing on both the 9.4 and 10.4 μm sequence bands. The alumina waveguide laser has 40 lines lasing on the 10.4 μm sequence band. These lasers can be either pulsed or continuous-wave (CW) operated on the selected line without a line jumping problem. Received: 29 September 1997/Revised version: 2 December 1997     

Coupling efficiency in grating tuned carbon dioxide waveguide lasers

The coupling efficiency in typical CO₂ waveguide lasers when the feedback element is a diffraction grating is investigated theoretically. A scalar diffraction integral approach is adopted, and the laser is assumed to operate on its lowest loss waveguide mode.     

A waveguide reactor for IR multiphoton dissociation and its application to13C laser isotope separation

A waveguide reactor for infrared multiphoton dissociation reactions has been presented and applied to laser isotope separation of¹³C. The reactor is a sealed vessel containing a hollow waveguide for a CO₂ laser, and the laser beam is condensed in the waveguide. The waveguide is a pipe of total-reflection glass or metal-coated glass with a funnelled inlet; it is 50 cm long with a 3 mm inner diameter. The isotope separation of¹³C has been made by multiphoton dissociation of CHF₂Cl using a TEA CO₂ laser. The result has shown that the waveguide reactor increases the dissociation yield by four to ten times as much as that without the waveguide at the pulse rate of up to 150 Hz, while the separation factor remains on the same level. It is also found that an optical breakdown which is induced at the wall surface plays a significant role to reduce the isotope selectivity.This work is for a partial fulfilment of B.S. degree of Osaka Electric Communication University     

Manufacturing of Nd:Gd3Ga5O12 ridge waveguide lasers by pulsed laser deposition and ultrafast laser micromachining

Laser radiation is used both for the deposition of the laser active thin films and for the micro structuring to define wave guiding structures for the fabrication of waveguide lasers. Thin films of crystalline and amorphous neodymium doped Gd₃Ga₅O₁₂ are grown on single crystal yttrium aluminium garnet by pulsed laser deposition using excimer laser radiation.Manufacturing of the laser active waveguides by micro structuring is done using femtosecond laser ablation of the deposited films. The structural and optical properties of the films and the morphology of the structured waveguides are determined in view of the design and the fabrication of compact and efficient diode pumped waveguide lasers. The resulting waveguides are polished, provided with resonator mirrors, pumped using diode lasers and the waveguide lasers are characterized. The spectroscopic properties of the amorphous waveguide are investigated and an infrared waveguide laser is demonstrated. To our knowledge, there have been no reports by other groups of the successful operation of a structured waveguide laser fabricated by this technique or of a waveguide laser made from amorphous neodymium doped Gd₃Ga₅O₁₂.     

Output mode characteristics of an in-phase locked gain waveguide array CO2 laser

In this paper,experimental and theoretical studies of the output mode characteristics of an in-phase locked gain waveguide array CO 2 laser are reported.The experimental results of the optical oscillation mode frequency,the far-field intensity distribution and the burnt pattern of the sliced waveguide array laser are obtained.A revised mode expression of the rectangle waveguide,which is suited for this waveguide array CO 2 laser,is proposed.The theoretical simulation results based on the revised mode expression are shown to be in good agreement with the experimental results.     

Facile liquid phase deposition of thick reflective GeO2 film for hollow waveguide delivery of CO2 laser radiation

A new idea of using LPD (liquid phase deposition) to prepare a GeO₂ thick reflective film for hollow waveguide delivery of CO₂ laser radiation was investigated in this work. The LPD process was achieved by designedly adding acid to GeO₂–aqueous ammonia. The addition of acid could induce the transformation of germanate ions into GeO₂ solutes, leading to the deposition of a GeO₂ ceramic film when the concentration of GeO₂ solute is higher than its saturation solubility. It was found that the highest film growth rate occurred at a pH value of 3, while a film with low surface roughness and good adhesion to the substrate was produced at a pH value of 2 and the film could be converted to a smooth, compact hexagonal GeO₂ film by heat treatment at 1120 °C for 30 min. Two abnormal dispersion bands within 7.6–9 μm and 9.6–11.2 μm were mainly caused by the silica glass substrate and the GeO₂ film, respectively. The film was thick enough to achieve the total reflectance of the CO₂ laser radiation. The use of this GeO₂ film in a hollow waveguide structure for CO₂ laser radiation delivery is discussed based on the transmission loss and the feasibility of the deposition of the GeO₂ film inside silica capillary tubes. The results show that the hollow waveguides with low transmission loss are most likely fabricated at a low cost using the LPD-derived GeO₂ reflective film. PACS 78.20.-e; 78.66.-w; 42.70.-a; 78.20.Ci; 78.40.-q     

Modelling of Tm3+-doped LiNbO3 Waveguide Lasers

In this work, CW laser operation of Tm³⁺-doped LiNbO₃ channel waveguides has been modelled. The model is based on time dependent laser rate equations coupled with the laser signal and pump photon flux equations. Steady state solutions for the population densities, pump and signal powers are obtained by using finite difference discretization of the active volume. The effects of spectroscopic parameters such as concentration dependent cross-relaxation and excess waveguide loss have been analyzed. We demonstrate good agreement with experimental data previously reported in Zn-diffused LiNbO₃:Tm³⁺ channel waveguide lasers. It is shown also that laser performance can be substantially improved by optimizing the cavity length.     

Praseodymium-doped Ti:LiNbO3 waveguides

3 by diffusion doping is investigated by means of secondary neutral mass spectrometry and secondary ion mass spectrometry. The diffusion of praseodymium in LiNbO₃ can be described by Fick’s laws of diffusion with a concentration-independent diffusion coefficient and a limited solubility of praseodymium in LiNbO₃ increasing exponentially with rising temperature. The diffusion depends on the Li₂O content of the LiNbO₃ crystal. For LiNbO₃ crystals with a nominal slight difference in the congruent composition, the diffusion constants and activation energies for Z-cut LiNbO₃ are 3.28×10^-5 cm²/s and 2.27 eV, and 1.39×10^-5 cm²/s and 2.24 eV, respectively. Titanium-doped waveguides are formed in Pr:LiNbO₃ and characterised in relation to waveguide loss and absorption in the visible and near infrared. Received: 17 September 1998 / Accepted: 11 November 1998     

射频激励板条波导CO2激光器远场空间压窄单峰输出模式特性的实验研究

报道了射频激励扩散型冷却板条波导CO₂激光器远场呈空间窄单斑分布的模式特性及其模式演化过程的实验现象,实验研究了远场出现压窄单斑时的模式结构.通过实验研究发现实验中所获得的近场呈多点分布和远场呈空间窄单峰分布的板条波导激光器输出模式是一种新的单模频振荡模式. 关键词：     

A DC excited waveguide multibeam CO2 laser using high frequency pre-ionization technique

High power industrial multibeam CO₂ lasers consist of a large number of closely packed parallel glass discharge tubes sharing a common plane parallel resonator. Every discharge tube forms an independent resonator. When discharge tubes of smaller diameter are used and the Fresnel numberN ≪ 1 for all resonators, they operate in waveguide mode. Waveguide modes have excellent discrimination of higher order modes. A DC excited waveguide multibeam CO₂ laser is reported having six glass discharge tubes. Simultaneous excitation of DC discharge in all sections is achieved by producing pre-ionization using an auxiliary high frequency pulsed discharge along with its other advantages. Maximum 170 W output power is obtained with all beams operating in EH₁₁ waveguide mode. The specific power of 28 W/m is much higher as compared to similar AC excited waveguide multibeam CO₂ lasers. Theoretical analysis shows that all resonators of this laser will support only EH₁₁ mode. This laser is successfully used for woodcutting     

Field distribution effects in laser driven diffusion through metal capillaries

A new approach for the IR laser driven diffusion through metal capillaries is reported in this paper. It reveals the influence of the inner distribution of the electromagnetic field on the resonant character of the diffusion of a mixture of SF₆ (resonant) and N₂ through an Ni capillary under IR irradiation. A waveguide model is proposed for the considered e.m. field-heterogeneous system interaction, an explanation for the persistence of the selective effects even at total pressures as high as 7 Torr being provided. Some spectral differences between the inside-capillary molecules and bulk-phase molecules are pointed out using a simple attenuation measurement method.     

Pulsed-laser deposition of a Nd:KGd(WO4)2 waveguide in Ar and O2 environments

Thin-film Nd-doped potassium gadolinium tungstate (Nd:KGW or KGd(WO₄)₂) waveguides are deposited on (1102)sapphire or (100)YAG substrates by KrF laser ablation of potassium-rich ceramic targets in Ar and O₂. The dependence of the stoichiometry, crystallinity and waveguide properties of the films on the environmental gas pressure and substrate temperature is studied. Highly textured crystalline (110) KGW films are grown. An optical waveguide loss as low as 3 dB/cm is obtained for the films grown in Ar. The as-grown films are optically active. Upon annealing at 900 °C in air, the crystallinity and the properties of the emission spectra are dramatically improved. PACS 81.15.Fg; 42.70.Hj; 78.20.Ek     

Frequency Stabilization of Waveguide CO2 Laser by a Digital Technique

In this work we present a simple technique for laser frequency stabilization, based on Digital signal processing. The technique is used to stabilize a waveguide CO₂ laser of wide tunability by using three kinds of reference signals: the CO₂ laser ouptut power, an infrared absorption optoacoustic signal and the output power of a Far-Infrared optically pumped molecular laser.     

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.     

Continuous-wave laser oscillation at 1.06 µm in silicon ion-implanted Nd:YVO<Subscript>4</Subscript> planar waveguide

This work, for the first time to our knowledge, reports continuous-wave laser oscillation at 1.06 μm in Nd:YVO₄ planar waveguide formed by 3.0 MeV Si⁺ ion implantation at a dose of 1 × 10¹⁵ ions/cm² at room temperature. The effective refractive indices of the waveguide propagation modes were measured by using a prism-coupling method after the annealing at 240°C for 60 min in air. The performance of the waveguide laser has been studied in terms of the threshold pump power and slope efficiency. The laser outputs show a very high stability operating in cw regime at room temperature.     

Side-wall emitting ZnSe/AlN waveguide CO2 laser

A side-wall emitting ZnSe/AlN waveguide CO₂ laser, which is able to extract the output power from the waveguide wall, is proposed. In the proposed scheme, four polished AlN plates are cemented to form a 16 cm long waveguide with 1.9×1.9 mm² cross section. One of the AlN plates is partially replaced by the ZnSe plate. This part is used as an output window. To confirm the workability of the proposed scheme, a trial laser was constructed and tested. The output power of several milliwatts was observed from the ZnSe waveguide wall.     

Mechanism and process of fabricating fluorinated polyimide optical waveguide by CO2 laser direct-writing

Fluorinated polyimide waveguides were fabricated by CO₂ laser direct-writing. The poly(amic acid) micro-region irradiated by CO₂ laser beam was studied with FT-IR micro-spectroscopy. The FT-IR spectra implied that the laser induced thermal-imidized polyimide was of optical anisotropy, and the imidization degree of exposed micro-region increased with the rising of output laser power. The increased aspect ratio of waveguide and smoothness of surface can be achieved by increasing the pre-cured temperature (below 120°C) and writing speed, and optimizing laser power and the distance between the lens and the annular aperture. The guided light was clearly confined to the core of the fabricated waveguide, which means this technique can be used for fluorinated polyimide waveguide fabrication.