Laser Tube Research Articles

Experimental study of self-injection locking oscillator on copper vapor laser

As a novel method to obtain a low divergence laser beam, a self-injection locking oscillator system has been developed for a copper vapor laser. The system is made of one laser tube, and uses temporal superposition of two pulsed discharges, predischarge and main discharge. The laser pulse is produced in the main discharge by amplifying a seeded laser pulse produced by the predischarge. By optimizing the discharge conditions including an interval period between the two pulsed discharges, a high quality laser beam containing 80% of the whole laser beam energy in divergence as small as eight times diffraction limited has been obtained. The quality of the laser beam is comparable to that obtained with a conventional injection locking oscillator system consisting of two separate laser tubes.

Experimental Investigation of CO2 Laser Assisted by Silent Discharge

A new type of CO2 laser tube has been designed by using a plasma tube having rectangular cross section and is excited by both axial DC glow discharge and transverse high frequency (HF) silent discharge. In this paper, the principle of the design is described briefly and its working characteristics, including of breakdown, V-A, laser power and efficiency, are studied experimentally and compared with those of CO2 laser excited by DC glow discharge only. Under the action of transverse HF silent discharge, the laser power, the laser efficiency, the gas-filled pressure and the fraction of N2 in this laser are increased significantly. In contrast, the breakdown voltage and the discharge voltage of this laser tube are decreased.

A 280-W average power Cu-Ne-HBr laser amplifier

A large-volume (19.5 L) laser tube has been built for the study of extrapolating power from the Cu-Ne-HBr laser medium. A high-power (50 kW) all-solid-state power supply has been also developed for this purpose. Results show a record optical power of 216 W extracted from this type of laser when used as an oscillator and 280 W as an amplifier.

Colorimetric Analysis in the Oral Lesion with White Light Laser

We developed the new colorimetric analysis system with the KOITO white light laser. The KOITO white light laser is a hollow cathode He-Cd laser device that simultane ously oscillates three light laser beams of three primary colors (red, green, blue) from a single laser tube. These beams are formed into a white light laser. In addition, because the oscillation wavelengths of red (635.5 nm, 636 nm), green (533.7 nm, 537.8 nm), blue (441.6 nm) color light are very near the ideal three primary colors.This system has three character. First character is non-contact type without integral sphere. Second is using pen-type probe which contain the bundle type fiber. Third is recording the rate to three colors in the standard reflex light.We examined the efficacy of this colorimetric analysis system with experimental study and clinical cases. On the other hand, we improved this system in the diagnosis of oral malignant tumor.Using this system, we could measure the color disorders in the oral cavity non-invasively, easily, immediately, exactly. Moreover we performed spectral analysis in patients with an oral squamous cell carcinoma. We found that there were bimodal peak at 650 and 690 nm at the excitation wavelength of 441.6 nm and that this result is different from the normal autofluorescenc.We consider that this coloriometric analysis system is useful to measure the color disorders in the oral cavity and has possibility to be improved in the diagnosis of oral malignant tumor.

Opening of lacrimal stenosis with endoscope and laser

Since the development of lacrimal endoscopes with which the mucosa and disorders of the lacrimal drainage system can be examined directly, the choice of surgical technique has changed decisively. Flexible miniendoscopes can be combined with a laser for the first time, allowing for exact localization of the stenosis and subsequent therapy. Between January 1996 and February 1997, 12 patients with acquired lacrimal stenosis were treated with an Hyb:erbium-YAG laser. After endoscopic localization, the stenosis or stricture was opened using the laser. Bicanicular intubation into the nose was performed and was left for at least 3 months. Five patients were treated for stenosis of the lower canaliculus and seven patients for postsaccal stenosis. The longest follow-up period was 22 months and the shortest 9 months. Treatment was successful in 4 cases with a canalicular stenosis, but restenosis occurred in all cases of postaccal stenosis and in 1 case of canalicular stenosis, and required a DCR. At this time we conclude that disorders of the canaliculi can be successfully treated with endoscopic localization, opening with a laser and subsequent silicone tube intubation. A high rate of restenosis may be expected in cases of postsaccal stenosis.

Generation of 275.4-nm UV output from a large-frame argon-ion laser for fluorescence detection in capillary electrophoresis

A standard, relatively old, large-frame argon-ion laser, which is available in many laboratories, was modified to produce output in the deep-UV (275–306 nm) region by installing a set of inexpensive, commercially available laser mirrors. The deep-UV output is generally applicable as excitation wavelength in the field of biochemical and environmental analysis. However, it has received little attention in the literature, probably because a complete laser set-up normally requires a high investment. The modification described, which includes a thorough cleaning of the Brewster windows of the laser tube and a careful alignment of the laser, is a good alternative to this investment. In daily operation, only some minor realignments are required. As an illustration of the applicability, excitation with the 275.4-nm line was used for laser-induced detection of native fluorescent aromatic sulphonates in capillary electrophoresis.

Advanced ArF excimer laser for 193 nm lithography

The ArF excimer laser light source will extend the optical lithography to below 0.18 μm design rules. Still under discussion is the most efficient layout of the stepper or scanner imaging optics, which has great impact on the laser-bandwidth requirements. Cost effective operation of a stepper or scanner tool requires a 193 nm excimer laser with high power and repetition rates in the order of 1 kHz or higher. Precise dose control of the exposure demands a high repetition rate and excellent stability of the laser output energy. We have developed an ArF laser which can be operated with up to 800 Hz repetition rate based on Nova Tube™ technology. Optimized materials and discharge configurations have been used to achieve laser tube lifetimes above 10 9 pulses. Up to 4 × 10 9 pulses tube lifetimes have been reported in beta-site tests. Gas lifetime of several 10 7 laser pulses is obtained. A solid-state switch has been adapted for the reliable and cost efficient operation of the 193 nm lithography laser. To achieve laser output of different bandwidths various resonator arrangements have been investigated. The paper gives an overview of the currently achievable power levels at different bandwidths and discusses future trends.

Fluorescence Counter-Staining of Cell Nuclear DNA for Multi-Color Laser Confocal Microscopy.

Twenty-one nucleic acid-specific fluorochromes were examined for use in cell nuclear counter-staining of specimens observed under a laser confocal microscope equipped with a Krypton/argon laser tube. Six green, three red, and two far-red fluorochromes gave sufficient fluorescence. Among them, SYBR Green I, Pico Green, SYTOX Green, YO-PRO-3, and TO-PRO-3 specifically stained the cell nuclear DNA. Other fluorochromes except POPO-3 stained the cell nuclear DNA and co-stained the cytoplasmic RNA. Conversely, POPO-3 specifically stained the cytoplasmic and nucleolar RNA. Anti-bleaching reagents (PPDA and DABCO) effectively prevented the photobleaching of SYBR Green I, Pico Green, YO-PRO-3, and TO-PRO-3, whereas DABCO accelerated the photobleaching of SYTOX Green. Taking into account the characteristics of these fluorochromes, SYBR Green I, YO-PRO-3, and TO-PRO-3 were best suited for cell nuclear counter-staining as green, red, and far-red fluorochromes, respectively. Especially, TO-PRO-3 seems to be the most useful because its far-red fluorescence enables three-color fluorescence staining by combination with immunofluorescence labeling with fluorescein and rhodamine derivatives.

Study on the kinetic mechanisms of copper vapor lasers with hydrogen-neon admixtures

The kinetic mechanisms of copper vapor lasers with hydrogen-neon admixtures are studied in detail with a computational model. (i) The copper particle density increases as the wall temperature rises after adding hydrogen into neon buffer gas, and de-population of the laser lower levels is enhanced during the interpulse period owing to a larger thermal diffusion loss from the tube center to the wall. (ii) The power dissipated by the thyratron or current through it decreases with increasing frequency of the momentum-transfer collision of electrons, i.e. the input power into the laser tube increases. On the other hand, the plasma electron temperature and electron density decrease as the electron energy is depleted through the impact excitation of the vibration levels of hydrogen, which makes the population of the laser upper levels restrained.

Self-organized fuzzy controller for multiwavelength frequency-stabilized <inline-formula><roman>CO</roman><sub><roman>2</roman></sub></inline-formula> laser

The stabilization of a multiwavelength CO2 is very complex. The difficulty arises from the physical process inside the laser tube, which causes some uncertainty and/or imprecise factors in control. In this case, fuzzy logic control is more appropriate. A self-organized fuzzy controller is presented. By means of this fuzzy controller, a dualwavelength frequency-stabilized CO2 laser with high precision can be controlled effectively, and a satisfactory result is obtained.

Ground-state depletion mechanisms in pulsed barium vapor lasers

Depletion of the metal vapor density from the central region of metal vapor laser tubes has recently been identified as an important factor limiting laser output. We have studied the mechanisms that deplete the ground-state metal density profile by measuring radially resolved population histories of neutral and ionic species during a “burst” (i.e., a pulse train of 20–30 excitation pulses) in a barium vapor laser (BVL). The observed spatiotemporal density behavior during the afterglow of the first shot in the burst agrees well with a simple model for diffusion and recombination, which we have used to show that the primary depletion mechanism during the establishment of steady-state conditions arises from the ambipolar diffusion of ions to the tube wall, and that gas-heating effects are secondary. Analysis of the steady-state (i.e., late-burst) afterglow behavior further reveals that the depletion is significantly greater than that expected from the measured barium ionization, particularly when operating at low barium densities at the wall; this we attribute to a large radial ambipolar field induced by the presence of ionized buffer–gas atoms on axis. The results show that it is important to reduce the time-averaged ionization in order to minimize ground-state depletion. The implications for power scaling of the BVL and other metal vapor lasers are discussed.

An enhancement of pump efficiency of a Ti:sapphire tube laser with an inner spectrum converter

An inner spectrum converter was employed to enhance the pump efficiency of a Ti:sapphire laser system. The inner converter was inserted along the hollow of the laser tube for additional spectrum conversions of the photons transmitted through the outer converter jacket and the laser-tube wall. The pump source was an array of hypocycloidal pinches that produced intense broad-band, rich in the near-ultraviolet, emissions. The increase of laser efficiency is attributable to the inner converter which offered an efficient spectral coupling into the center of the Ti:sapphire absorption band and a better geometric coupling than the outer converter.

CO2 Laser Excited by Microwave Discharge Using Stripline.

Recently a CO2 laser excited by microwave discharge has been studied to achieve higher efficiency and a lower cost laser system. In this study a stripline was used to guide microwave with TEM mode. This mode has almost homogeneous intensity distribution of electric field and almost homogeneous discharge could be obtained. In the experimental set-up, 2.45 GHz microwave power was fed to an antenna mounted in a rectangular waveguide. Microwave with TE10 mode was propagated through space in the waveguide, then transformed into TEM mode with the obliquely connected stripline. A laser tube (25 mm-bore) was inserted perpendicularly to the stripline. The gas mixture used in this work was He:Ne:CO2 = 81:15.6:3.4. The maximum output power of 56 W (9.5 % efficiency) and the maximum efficiency of 12.6 % (34.2 W output power) were obtained at 25 Torr gas pressure.

エキシマーレーザー励起用大気圧放電におけるグローとアークの形成

Factors leading to glow or arc discharge in atomospheric pressure of an excimer laser tube are studied. Arc and glow discharge are realized by choosing range of the applied voltage to the excitation circuit of the laser. Too low voltage to the excitation circuit of the laser is proved to cause arc discharge. Spectra of the emission from the discharge tube are observed. Energy distribution of the gas and electrons are discussed from the observed spectra. It is found that impurities affect the average energy of electrons and that molecules with many levels in low energy also cause arc discharge.

A study on selected properties of La1-xSrxCoO3 and its application in sealed CO2 lasers

Samples in the composition series La1-xSrxCoO3 with x = 0-0.8 were synthesized, and their crystal structures, conductivities and catalytic activities were studied. When x < 0.6, they have a rhombohedrally distorted perovskite structure. When x = 0.3-0.5, their conductivities at room temperature are of the order of 10(3) S m(-1). When the temperature is higher than 250 degrees C, the catalytic activities of La1-xSrxCoO3 were very high which reaches a maximum for the sample at x = 0.3. Cylindrical samples were made from La1-xSrxCoO3 x = 0.3 and used as a cathode in sealed CO2 lasers. Compared to the traditional Ag-Cu alloy cathode, the performance of La0.7Sr0.3CoO3 is better. The maximum output of a 1.0 m length laser tube using the new cathode is 53.1 W m(-1).

Optical characteristics of a rectangular bore discharge-excited Sr+ recombination laser

We report results of studies of laser beam divergence, laser beam intensity profiles and spatial and temporal laser pulse characteristics for a rectangular bore strontium recombination laser operating on the 430.5 nm Sr transition at high pulse rates (3-10 kHz). Beam divergence is found to be very nearly diffraction limited for a flat-flat optical cavity, with a very uniform spatial distribution of laser intensity under optimum operating conditions. Laser pulse characteristics provide an indication of plasma conditions across the laser tube.

Terrestrial solar-pumped iodine gas laser with minimum threshold concentration requirements

A t-C4F9I iodine gas laser pumped by concentrated uv terrestrial solar radiation was designed and built. The laser consists of an optical resonator cavity, a blowdown lasant gas flow system, and a parabolic trough reflector. The optical resonator design was based on a mathematical model that used iodine gas kinetic rate equations to predict threshold pumping power, available pumping power, and laser output power for various dimensions. An optimum design for this demonstration project was selected to minimize lasing threshold solar concentration to 40 suns, and retain a 15-min run time with our limited lasant supply. Output power was not optimized, and is predicted to be low (20 mW). An estimate of local spectral uv terrestrial irradiation was developed from band and total irradiation measurements. It was used to estimate solar concentration required to initiate lasing and laser output power. The laser, gas flow system, and parabolic trough collector were built and evaluated. Irradiation at the parabolic trough's focus (where the laser tube was placed) was measured for directional and total irradiation. These measurements showed an average solar concentration of 15-20 suns below threshold. The study establishes the feasibility of terrestrial solar-pumped iodine lasers with low threshold, and simple, stable, and controllable lasant flow systems.

Time-resolved plasma diagnostic by laser-diode spectroscopy

A tunable diode laser has been used as a light source for line-of-sight absorption and Doppler-shift measurements. We have applied the method to perform plasma diagnostics in a magneto plasma dynamic (MPD) pulsed propulsor device and of an Ar/sup +/ laser tube plasma. Spectrally resolved argon absorption lineshapes of transitions of neutral and single ionized argon were recorded. A high temporal resolution (a few microseconds) is achieved by fast tuning the laser frequency at a repetition rate greater than 100 kHz. From the recorded spectra, we deduce the dynamics of the neutral components of the plasma in the thruster. We also demonstrate the possibility of direct ion diagnostics by the observation of ionic transitions, using red diode lasers in an Ar/sup +/-laser commercial tube.

New KrF and ArF Excimer Lasers for Advanced Deep Ultraviolet Optical Lithography

Advanced deep ultraviolet (DUV) optical lithography requires reliable high repetition rate excimer lasers at low cost of ownership. We optimized all components of the laser cavity. The result is a new metal/high-density ceramic laser tube with long life discharge components. It meets the specifications of the next generation of DUV laser sources. The new laser cavity was tested in several test runs at 193 nm (ArF) and 248 nm (KrF) and demonstrated excellent gas lifetime data when compared to conventionally designed lasers. For the first time a KrF laser was successfully operated in a quasi sealed-off mode for more than 1 billion pulses. The lifetime data of narrow bandwidth lasers necessary for DUV optical lithography tools also increase significantly. A 500 Hz 6 W laser with a bandwidth of 0.9 µ m passed in a marathon test 1.1 billion pulses and the gas lifetime exceeded 200 million pulses routinely. Additionally, we operated this laser at 8 W average power and 600 Hz.

Study of a high-powered He–Ne laser having rectangular discharge cross section

A rectangular cross-section discharge tube has been used to design and make a high-powered He–Ne laser. The output power of this kind of He–Ne laser can be raised by increasing the transverse size of the discharge tube. A He–Ne laser tube of 20×4.5 mm2 rectangular cross section and 1.7 m discharge length can give an output power of above 200 mW at 0.6328 μm. In this article, the design principle and the preliminary experimental results of this kind of He–Ne laser are briefly described and discussed.