Activities on diode pumped alkali laser (DPAL) in Japan are updated. Since the last presentation in Chengdu, we have continued our DPAL research mainly targeting the development of tools for future scaling-up and high-efficiency operation. In particular, the focus is on a numerical simulation that combines computational fluid dynamics (CFD) and wave optics. To confirm the agreement between the experimental and simulation results, we designed and built several experimental apparatuses. Our latest gas-flow type DPAL produced 15.5 W output power with 80% slope efficiency based on the absorbed pump light. The agreement with theoretical prediction was excellent not only for output power but also for transverse mode shape and beam quality. Additionally, to accurately predict the performance of Cs DPAL, we measured the main reaction cross sections, namely, mixing and quenching reaction cross sections of the two P states of Cs with various hydrocarbon buffer gases. The main result of the repetitive pulsed operation by the cavity dumping technique and relevant numerical simulation is also discussed.
We demonstrate a low-concentrated solar-pumped fiber laser with all-inorganic cesium lead halide perovskite quantum dots (QDs), which function as a sensitizer. The perovskite QDs exhibit substantial advantages for solarpumped laser applications because of their broad absorption and narrow emission spectra with high quantum yield. We successfully tuned the peak emission wavelength of the perovskite QDs by altering the I/Br ratio in order to achieve spectral overlap with Nd3+ ions, which have been widely used as a laser medium for solar-pumped lasers. The measurement results show that the laser output power is highly sensitive to the peak emission wavelength of the QDs. Although our synthesized QDs have a quantum yield of approximately 65%, which is less than that of conventional organic dyes, the laser performance was comparable because the fluorescence spectrum is tailored to the Nd3+ absorption band.
Unstable optical resonators employing graded reflectivity mirrors (GRMs) for diode-pumped alkali laser (DPAL) are theoretically studied. In this study, a wave optics resonator model was coupled with a simplified gas flow model. The platform modeled was a 100-W class Cs DPAL proposed by us. As the pump beams are obliquely incident to the active medium, a wide gain region appears compared with that of the axially pumping scheme. Although an unstable resonator was expected to be suitable to provide a high-quality output beam, it was found to be inapplicable for our relatively small-scale DPAL apparatus. Instead, we demonstrated that the application of a GRM unstable resonator provide a nearly diffraction-limited beam (M2 < 2) with minimal penalty for the output power. The effect of the gas flow on the beam quality is also discussed.
Cesium diode pumped alkali lasers (DPALs) have been operated using various hydrocarbons (methane, ethane, and propane) and helium as a buffer gas. We find that the optimum partial pressure of hydrocarbons depends on the cross sections of the upper-state mixing reaction, while the maximum output power does not depend on the hydrocarbon species. Because the cross section of the quenching reaction between cesium and these hydrocarbons is significantly smaller than that for the upper-state mixing reaction, no direct measurement of such cross sections has been attempted to date. In this study, we attempted to determine the cross sections with the aid of DPAL simulation. Output power calculations were repeated by varying the quenching cross sections until a reasonable agreement with the experiments was met. The results indicated that the quenching cross sections of methane, ethane, and propane were 0.05 ± 0.03, 0.14 ± 0.04, and 0.23 ± 0.07 Å2, respectively. The validity of the results is supported by the fact that the cross section of methane obtained is consistent with that suggested by Yacoby et al. [Opt. Express 26, 17814 (2018)].
In this paper, we demonstrate an extremely low-concentrated solar-pumped laser (SPL) that uses a transversely excited fiber laser geometry. To eliminate the need for precise solar tracking with an aggressive cooling system and to considerably increase the number of laser applications, low-concentration factors in SPLs are highly desired. We investigate the intrinsic low-loss property of SiO2 optical fibers; this property can be used to compensate for the extremely low gain coefficient of the weakly-pumped active medium by sunlight. As part of the experimental setup, a 40-m long Nd3+-doped SiO2 fiber coil was packed in a ring-shaped chamber filled with a sensitizer solution; this solution functioned as a down-shifter. The dichroic top window of the chamber transmitted a wide range of sunlight and reflected the down-shifted photons, confining them to the highly-reflective chamber until they were absorbed by the Nd3+ ions in the active fiber. We demonstrated a lasing threshold that is 10 times the concentration of natural sunlight and two orders of magnitude smaller than that of conventional SPLs.
A scalable pumping method for a diode-pumped alkali laser (DPAL) is proposed. In the past, pump beams were collinearly or transversely arranged to the optical axis of the optical resonator. In our proposal, pump sources are circularly arranged around the optical axis, and the pump beams irradiate the gain cell at a small (0.1 radians) angle from the optical axis. Tens of pump beams can be coupled to the gain medium with high circular symmetry and high coupling efficiency. The idea was verified by numerical simulation, and the results were validated by experimental investigation.
We have developed a small-scale, diode-pumped alkali laser with a closed-loop gas circulation device and investigated the effect of gas circulation on the laser output power. The gain cell, with a 5 cm active length, is fitted with antireflection windows, and a cross-flow fan is incorporated inside it. The active medium is composed of cesium, hydrocarbon, and a buffer gas whose total pressure is approximately 2 atmospheres. The laser output power was measured as a function of the gas flow velocity for different buffer gases. In the case of argon, the laser power was strongly dependent on the gas flow velocity, whereas it was almost independent of the gas flow in the case of helium. The maximum output power of the argon buffer was close to that of the helium buffer when the gas velocity exceeded 6 m/s. The experimental results were in good agreement with the numerical simulations.
A theoretical study has been conducted for investigating the possibility of a diode-pumped alkali laser (DPAL) operating in repetitive pulsed mode. A one-dimensional, time-dependent rate-equation simulation of a Cs DPAL was developed to calculate the dynamic behavior of the active medium when Q-switching or cavity dumping was applied. The simulation modeled our small-scale experimental apparatus. In the continuous-wave (CW) mode, the calculated output power was in good agreement with the experimental value. Q-switching was shown to be ineffective because of the short spontaneous lifetime of the active medium, on the order of 10 ns. On the other hand, cavity dumping was proven to be effective. In typical operational conditions, a 54 times increase in peak power with respect to the CW power was predicted.
A numerical simulation code for a diode pumped alkali laser (DPAL) was developed. The code employs the Fresnel- Kirchhoff diffraction integral for both laser mode and pump light propagations. A three-dimensional rate equation set was developed to determine the local gain. The spectral divergence of the pump beam was represented by a series of monochromatic beams with different wavelengths. The calculated results showed an excellent agreements with relevant experimental results. It was found that the main channel of the pump power drain is the spontaneous emission from the upper level of the lasing transition.
Activities on diode pumped alkali laser (DPAL) in Japan is reviewed. We have started alkali laser works in 2011, and currently, we are the only players in Japan. Our interests are application oriented, and it is not only defense but also industrial. DPAL is a good candidate as a source of remote laser machining, thanks to its scalability and extremely good beam quality. We are studying on scientific and engineering problems of Cs DPAL with a small-scale apparatus. A commercial diode laser with volume Bragg grating outcoupler is used to pump the gain cell longitudinally. A 6.5 W continuous-wave output with optical to optical efficiency of 56% (based on the absorbed power) has been achieved. Numerical simulation codes are developed to understand the physics of DPAL and to help future developments.
A small-scale cesium diode-pumped alkali laser (DPAL) apparatus has been developed for fundamental researches. A commercial laser diode with volume Bragg grating outcoupler is used to pump the gain cell longitudinally. Both windows of the gain cell are set at Brewster’s angle for minimum loss and maximum durability. Output coupling coefficient is continuously variable from 13% to 85% by the slanted quartz plate outcoupler inserted in the optical resonator. Small signal gain is measured with a laser diode probe at various gain cell temperatures. A 6.5 W continuouswave output with 56% optical-to-optical conversion efficiency (based on the absorbed power) has been achieved. A numerical simulation code is developed and its calculation results are in good agreement with the experiments.
An investigation of exciplex pumped alkali laser (XPAL) has been conducted. A 4-cm gain cell containing Cs as an
active medium is pumped by a tunable Ti: sapphire pulse laser. Laser oscillation is observed in both five-level and four-level
systems. Small signal gain and saturation intensity of the active medium is measured by both probe laser
amplification and oscillation experiment with varied output coupling. A one-dimensional numerical simulation is
developed and the result of calculations is compared with the experiments. The pulse shape and oscillation threshed
agree reasonably while calculated optical-optical conversion efficiency is underestimated.
Output power enhancement of an all gas-phase iodine laser (AGIL) by addition of hydrocarbon gases is studied. It is
expected because hydrocarbon gases might scavenge Cl atoms, which are strong quencher of the upper state of the laser
medium, I(2P1/2). In AGILs, suppression of the Cl atom concentration is the key to improving the efficiency of laser
operation because Cl atoms are inherently generated by the self-annihilation of the energy donor, NCl(a1Δ). We found
that the addition of CH4 gave the best results because of its high scavenging rate constant and inertness to I(2P1/2). An
enhancement of 10% was observed in the output power when CH4 was added at a flow rate twice that of NCl3. On the
other hand, when C2H4 or C2H2 were added at the same flow rate as that of CH4, the output power reduced despite their
fast removal rate of Cl atoms. The reason for the reduced output power was that the unsaturated bonds scavenged not
only the Cl atoms but also the H atoms, resulting in a low density of H atoms, and this decelerated the production of
NCl(a1Δ). The observed laser characteristics could be reasonably explained by numerical model calculations.
The characteristics of an all gas-phase iodine laser (AGIL) that uses molecular iodine as a source of iodine atoms is
studied. The laser is based on the energy transfer reaction between metastable NCl(a1Δ) and ground state I(2P3/2) atoms,
which are produced by the electric discharge of a mixture of I2 and He. At fixed flow rates of the chemical species, the
laser output powers are measured at three different positions in a flow reactor. The output power is characterized by a
function of the optical axis position and is reasonably reproduced by the numerical calculation. A repetitive pulse of laser
output at 50 Hz with a duty factor of 40% is observed. The highest output power is 40 mW at 210 mm downstream from
the mixing point of I/H/He and NCl3. This is 80% of the output power generated from the conventional system using HI
as an iodine donor. The measured results of the time resolved laser output power suggest that the output power of the I2-
AGIL is more sensitive to the electric discharge plasma intensity as compared to that of the HI-AGIL. An AGIL operated
using I2 could potentially have the same output power as that of an AGIL operated using HI if a continuous-wave electric
discharge generator is used.
A computational model of the cross-flow type singlet oxygen generator (SOG) for chemical oxygen-iodine laser (COIL)
is developed. The reaction zone, in which basic hydrogen peroxide (BHP) jets flow downwards and chlorine flows
transversely, is discretized in two dimensions. Chemical and physical processes are calculated in each cell, the gas and
liquid transport is modeled by a geometrical transfer rule. The processes involved in this SOG model are surface reaction
between the gas-phase chlorine and the liquid-phase HO2- ion, surface ion renewal by the diffusion process, heat release
by the chemical reactions, heat exchange between gas and liquid phases, water evaporation and condensation,
homogeneous deactivation of O2(1Δ), and heterogeneous deactivations of O2(1Δ) by the liquid column surfaces. We
develop a 80 mmol/s-class SOG to validate the developed model. It is shown that the Cl2-O2 conversion efficiency
(utilization) and O2(1Δ)/O2 ratio (yield) are in good agreement with the theoretical model in a wide range of operational
conditions. Heterogeneous deactivation probability affects the model prediction markedly, and 1×10-3 yields the best
agreement with the experimental results. This supports the values in previous publications.
Laser processing of sheet metals are performed with a 2 kW cylindrically polarized CO2 laser. Drilling and cutting
capabilities are compared between conventional circular polarization and radial/azimuthal polarization beams of the
same power. A 9 mm-thick mild steel is drilled with O2 assist and azimuthal polarization shows a 15% faster drilling rate
than circular polarization. A 4.5 mm-thick mild steel is cut with O2 assist and radial polarization shows a 50% faster
cutting speed than circular polarization. Smaller surface roughness of the cut is obtained by the radial polarization. A 2
mm-thick stainless steel is cut with high-pressure N2 assist. Although no difference of the maximum cut speed between
radial and circular polarizations are seen, it is possible to reduce the assist gas pressure from 0.6 MPa to 0.3 MPa in the
case of radial polarization.
A 2kW cylindrically polarized laser beams by using a triple-axicon optical resonator is demonstrated. The rear mirror of
a commercial CO2 laser is replaced by the optical component that is composed of a waxicon and an axicon accurately
fitted together. Selection of the polarization is made by the reflectivity difference between p and s polarizations at the
inclined surfaces. The reflectivity is designed to rs>rp so that the resonator is oscillated in azimuthally polarized mode.
The output beam is converted to radially polarized beam by a converter composed of four λ/4 phase retarders. The
polarization conversion efficiency is 98.5% and the power conversion efficiency is 95%.
KEYWORDS: Chemical species, iodine lasers, Iodine, Hydrogen, Mirrors, Numerical simulations, Energy transfer, Chemical oxygen iodine lasers, Chlorine, Chemical reactions
Theoretical and experimental studies of the amine-based all gas-phase iodine laser (AGIL) are conducted. The numerical
simulation code is a detailed one-dimensional, multiple-leaky-stream-tubes kinetics code combined with all the known
rate equations to date. Using this code, we find that the key reactions to achieve positive gain are the deactivation
reaction of excited iodine atoms by chlorine atoms and the self annihilation reactions of NCl(1Δ). The order of the
injection nozzles is crucial to suppress these reactions. Following the calculations, we fabricate a flow reactor apparatus
and demonstrate laser action for the 2P1/2-2P3/2 transition of iodine atom pumped by energy transfer from NCl(1Δ)
produced by a set of amine-based, all gas-phase chemical reactions. Continuous-wave laser output of 50 mW with 40%
duty factor is obtained from a stable optical resonator consisting of two 99.99% reflective mirrors. The observed laser
characteristics are reasonably explained by numerical calculations. To our knowledge, this is the first achievement of
amine-based AGIL oscillation.
Numerical simulation and flow-tube experiments are conducted to understand the chemistry of an amine-based all gasphase
iodine laser (AGIL). The numerical simulation code developed is a one-dimensional, multiple-leaky-stream-tubes
kinetics code combined with all the known rate equations to date. Using this code, we find that the key reactions to
achieve positive gain are the deactivation reaction of excited iodine atoms by chlorine atoms and the self annihilation
reactions of NCl(1Δ). The order of the injection nozzles is crucial to suppress these reactions. Flow reactor experiments
are conducted based on these calculations, and small signal gain is measured. When NCl3 is not supplied, absorption of
the I(2P1/2)-I(2P3/2) transition is observed. When NCl3 is supplied, the absorption is decreased and the dip occasionally
turns to the hump, corresponding to a small signal gain of 5×10-3 %/cm. To our knowledge, this is the first observation
of positive small signal gain of the amine-based AGIL system.
An optical resonator for generating high-power, cylindrically polarized beams is demonstrated. The rear mirror of a
commercial CO2 laser is replaced by a novel triple-axicon retroreflector unit that is composed of a waxicon and an
axicon accurately fitted together. Selection of the polarization is made by the reflectivity difference between p and s
polarizations at the inclined surfaces. The resonator is designed for radially polarized oscillation, however, the output
beam is azimuthally polarized because the oscillation occurs at unexpected 9.6 μm. A stable 1 kW output is generated,
and the measured beam quality is M2=2.0.
Numerical simulation and flow-tube experiments are conducted to understand the chemistry of the amine based all gas-phase
iodine laser (AGIL). The numerical simulation code developed is a one-dimensional, multiple-leaky-stream-tubes kinetics code combined with all the known rate equations to date. The validity of the code is confirmed to compare the calculated results with experimental results reported elsewhere. We find that the key reactions to achieve positive gain are the deactivation reaction of excited iodine atoms by chlorine atoms and the self annihilation reactions of NCl(1Δ). The order of the injection nozzles is crucial to suppress these reactions. It is shown that positive gain is possible with optimized flow rates and nozzle positions. Flow reactor experiments are conducted based on these calculations, and small signal gain is measured. The results are compared with the calculations.
Optical resonator for generation of high-power radially polarized beam is presented. In laser cutting applications, radially
polarized beam is advantageous because the beam contacts the cut front always with the highly absorptive p-polarization. The proposed resonator comprises a reflector unit that has three conical faces with polarization sensitive dielectric coating, and an ordinary output coupler. The resonator is compatible with any existing circular mirror standing-wave optical resonators. Numerical simulation shows good polarization selectivity with only 1% of reflectivity difference between p and s polarizations, and M2 factor of the output beam is 1.9. No output power degradation is seen compared to the standard spherical mirror resonator. Design and fabrication of the resonator for a 1kW-class commercial cw CO2 laser is discussed.
Method of direct oscillation at radially or azimuthally polarized transverse modes in an optical resonator is presented. The optical resonator consists of a w-axicon, a polarization controlling feedback axicon mirror, and a flat output coupler. The central axicon of the w-axicon is made to slide forward and backward relative to the outer axicon, that leads to the selection of the arbitrary order of the LG0±l Laguerre-Gaussian modes. By selectively suppressing the p-polarization or s-polarization of the axicon reflector, the oscillation modes are forced to the radially or azimuthally polarized. A preliminary experiment proves such a resonator is viable and numerical simulation predicts the oscillation characteristics of the proposed resonator.
An advanced nozzle, also known as ejector nozzle, suitable for a 500 W class COIL employing an active medium flow of nearly 12 gm/s has been developed and used instead of conventional slit nozzle. The nozzle has been tested in both cold as well as hot run conditions of COIL achieving a typical cavity pressure of nearly 10 torr, pitot pressure of ~ 85 torr and a cavity Mach number of ~2.5. The present study details the gas dynamic aspects and detailed numerical studies of this ejector nozzle and highlights its potential as a COIL pressure recovery device. This nozzle in conjunction with a diffuser is capable of achieving pressure recovery of ~ 60 torr, equivalent to the much cumbersome first stage of the pressure recovery system used in case of conventional slit nozzle based system. . Thus use of this nozzle in place of conventional slit nozzle can achieve the atmospheric discharge using single stage ejector system thereby making the pressure recovery system quite compact.
KEYWORDS: Iodine, Chemical lasers, Chemical oxygen iodine lasers, Oxygen, Molecules, Nitrogen, Industrial chemicals, Systems engineering, iodine lasers, Laser systems engineering
Supersonic chemical oxygen-iodine laser (COIL) with an advanced mixing nozzle is studied. The mixing nozzle consists of a staggered arrangement of thin wedges lying across the flow duct. Its unique shape looks the letter “X” when it is viewed from the side. To use the new arrangement of iodine injector and the X-wing nozzle, 599W of output power with a chemical efficiency of 32.9% was achieved. This is the highest chemical efficiency of any supersonic COIL reported to date.
This paper reports on a trace gas monitor using a dual wavelength coherent light source. The laser spectrometer is based on difference frequency generation (DFG) techniques in a periodically poled lithium niobate (PPLN) crystal, naturally having two laser sources (i.e., signal and pump laser sources) in it. A newly proposed idea is to use residual signal DFB-LD power to tune to NH3 absorption lines around at 1.536 μm when the DFG output wavelengths are accessed at 3.46 μm. In the experiments, the signal DFB-LD was carefully tune the wavelength guided by HITRAN database in order to select appropriate mid-IR absorption lines of NO2, while the DFB-LD can detect simultaneously NH3 absorption lines. As results, both gaseous species were detected successfully with the same multi-pass optical cell in one DFG spectrometer scheme. Spectroscopic data both in near-IR and in mid-IR region, simulating flue gas condition are discussed in detail.
A 3.6M basic hydrogen peroxide solution is electrochemically regenerated. The apparatus was originally developed for electrolytic H2O2 production, generating dilute (<0.2M) BHP for paper manufacturing. To suppress decomposition by various mechanisms, they are identified and quantified. Both caffeine and peracetic acid are found effective to suppress autodecomposition. Theoretical prediction of the current efficiency is made to find an optimum operational condition. A BHP of 3.614M is regenerated to 3.657M with a current efficiency of 67%.
We have been studying the Chemical Oxygen-Iodine Laser (COIL) Thermal Image Marker System to the far field objects. This system can mark the distinguishable thermal image on the far field objects with the laser beam of the COIL to guide the Imaging Infrared homing air vehicle to the object marked thermal image with pinpoint accuracy. For the development of this system the study of the COIL resonator is the main task to meet the generation of the required high quality laser beam.
Therefore, first we made two kinds of the experiments. One is to generate the distinguishable thermal image mark (TIM) on the object with stable resonator of the 13 kW output COIL system in the near field. Another is to improve the laser beam quality with the unstable resonators of the COIL system in the low gain condition. Then we studied the high power unstable resonator design for this system with the numerical simulation based on its experimental data and the two-dimensional Fresnel-Kirchhoff integration method with partially coherent scalar electric field. Finally we made the numerical far field TIM generation to verify the TIM generation with the laser beam of the studied high power unstable resonator. The result of simulation shows the fine TIM generation.
The result of the experiment and the resonator design study shows that it is possible to realize the good thermal image mark, the good quality laser beam and the promising unstable resonator for the COIL Thermal Image Marker System.
Mist singlet oxygen generator (Mist-SOG) has been developed in order to increase the BHP utilization. On the other hand, Mist-SOG generates much more water vapor than conventional SOG because the heat capacity of the BHP is small. It is well known that the water vapor deactivates the excited iodine. In order to remove the water vapor, we developed a jet-cold trap. In this method, a nozzle sprayed a chilled H2O2 at 238K with a thin layer form to the gas flow directly in order to get the large specific surface for the water vapor. As a result of experiment, Water vapor partial pressure reduced from 3.3 Torr at the BHP flow rate of 2.2 ml/s and Cl2 flow rate of 3.5 mmol/s for the 65µm BHP droplets.
Regeneration of Basic Hydrogen Peroxide (BHP) for Chemical Oxygen Iodine Laser (COIL) has been studied. The apparatus is an electrolyte H2O2 generator, which is composed of anode chamber, cathode chamber with gas diffusion electrode and cation exchange membrane. BHP containing 5 to 10 weight percent (wt%) of H2O2 is supplied to the apparatus and the change in the H2O2 concentration is measured for various operational conditions. A 5.11wt% BHP is regenerated with current efficiency of 92% and a 10.4wt% BHP is regenerated with current efficiency of 73%. It is found that the BHP flow rate and temperature of the BHP are critical to obtain high current efficiency.
Pulsed oscillation of chemical oxygen-iodine laser, which is comprised of a pulsed singlet oxygen generator (SOG) and a photolytic iodine laser, is studied. This scheme allows one to produce a large aperture and high-pressure laser medium while maintaining a minimum degradation of stored energy by water vapor. The experimental apparatus consists of a porous pipe SOG, an iodine donor (CH3I) injector, a flash lamp and an optical resonator. Laser oscillation experiments are conducted and the operational characteristics of the apparatus are investigated. Pulse duration is inversely proportional to the iodine donor concentration as expected. The oscillation capability for different iodine donors is studied and it is concluded that the iodine donors containing fluorine are not suitable for the proposed scheme. Unfavorable chemical dissociation of iodate, which was observed in the previous study, is avoided by the optimization of the iodine donor injection and flash exposure timings. Maximum output energy of 730mJ with pulse duration of 65μm is obtained.
Mixing enhancement technique of supersonic chemical oxygen-iodine laser (COIL) is studied. The difficulty of supersonic mixing due to the compressibility of the fluid has been overcome by the introduction of streamwise vortex into the flow. The developed nozzle is a staggered array of wedges, looks like “X” letter from the side of the flow duct. Computational fluid dynamics (CFD) is employed for the design optimization of the proposed mixing nozzle. A remarkable mixing condition is found when iodine injector is located at the exit plane of the mixing nozzle. Experiments are conducted and good agreement with calculation is obtained in terms of iodine molecule distribution. A 266W of output power with chemical efficiency of 14.6% is obtained and good mixing capability of the proposed nozzle design is confirmed.
Singlet Oxygen Generator ( SOG ) with a novel approach has been designed and fabricated. Singlet oxygen is taken out of the SOG at an angle of 40° thus avoiding the carry over of droplets, which is one of the major drawbacks of horizontal system. The paper discusses various design parameters for such type of SOG. For flow rates of chlorine up to 22 mmol/sec, the chlorine utilization and singlet oxygen yield have been observed to be ~ 90% and ~64% respectively.
A twenty-years of COIL researches and developments in Japan are reviewed. The researches of four major sites, namely, Keio University, Industrial Research Institute, Kawasaki Heavy Industries and Tokai University are presented in order of time. Epoch-making works are highlighted, and the significance of those works in the industrial COIL development is discussed, Finally, current status of COIL researches in Japan is introduced.
Raman spectroscopy using a simple external Power Build-up Cavity (PBC) pumped with a diode laser was demonstrated. The PBC is very simple configuration consisted of anti- reflection coated low power (10mW, (lambda) equals670nm) laser diode, Graded index (GRIN) lens, and extremely high finesse external cavity, where the beam intensity can reaches up to 100W intracavity beam. Such a high finesse external cavity could optimized parameter attribute to high spectral brightness mostly suitable for a compact Raman light source without any sophisticated temperature and/or current injection control. PBC pumped Raman spectrum was measured by an optical fiber coupled optical multi-channel analyzer (OMA). The Raman signal from intracavity beam was imaged on the optical fiber by two focusing lenses (fequals38mm, 50mm) located in perpendicular to the optical axis. Stokes Raman spectra of N2 and O2 of gas mixture were simultaneously measured with real time operation, approximately.
KEYWORDS: Oxygen, Chemical oxygen iodine lasers, Chemical lasers, Liquids, Hydrogen, Industrial chemicals, High power lasers, Iodine, Energy transfer, Physics
New type mist singlet oxygen generator (Mist-SOG) for the chemical oxygen-iodine laser (COIL) has been developed. This SOG is devoted to make the liquid recirculation unnecessary with the complete reaction through a single pass of basic hydrogen peroxide (BHP). 75% of Cl2 utilization and 76% of O2(1Æ) yield were obtained with Cl2 molar flow rate of 3.0 mmol/s. H2O2 utilization in the BHP was achieved as high as 12.3%. This value is about 24 times larger than that obtained by the liquid-jet SOG.
A new strategy for pulse oscillation of chemical oxygenÑiodine laser based on a combination of a porous pipe SOG with an instantaneous atomic iodine generation, has been developed to seek the potential of COIL as an amplifier of the nuclear fusion driver. This new scheme allows one to produce a large aperture high pressure laser medium, which is favorable to the laser amplifier, while maintaining a minimum degradation of stored energy by water vapor. The experimental apparatus consists of the porous pipe SOG, an iodine donor (CH3I) injector, a flash lamp for the iodine dissociation, and an optical resonator. Operational characteristics of the apparatus including dependence of output energy on an iodine concentration was studied. As the result, the maximum output energy of 800mJ was obtained. It was also found that the CH3I was dissociated through unidentified chemical reaction associated with the O2(1Æ).
A study of chemical oxygen-iodine laser (COIL) for the use of decommissioning and dismantlement of nuclear facilities is conducted. A scaled-down model was developed as a prototype. Laser duct and optical cavity were designed so that it can be operated in both supersonic mode and high-pressure subsonic mode for the comparative study. A 1.34kW output with chemical efficiency of 24.6% was obtained in the supersonic mode. In the high-pressure subsonic mode, output power was 1 .12kW with chemical efficiency of 20.6%. A subsonic operation at 12Torr was demonstrated for the first time. A preliminary experiment of thick steel cutting was demonstrated by the developed system. The obtained data was in good agreement with published data.
High-pressure subsonic mode operation of chemical oxygen- iodine laser (COIL) is studied. In this mode, the singlet oxygen generated by the liquid-jet singlet oxygen generator (SOG) is directly utilized in the optical cavity without supersonic expansion. Drastic reduction of the required vacuum pump capacity, and iodine consumption was obtained. We have demonstrated a 25.0 percent of chemical efficiency with a small-scale device. The scale-up version of the COIL is developed and initial tests are conducted. The device is so designed that it will operate for 2 hours at 1kW laser output. Due to the inadequate heat exchanger of basic hydrogen peroxide (BHP), performance of the system was not yet satisfactory. However, a 30-minute continuous operation o the counter-flow type jet SOG with recirculation of BHP was demonstrated for the first time.
Output power enhancement of Chemical Oxygen-Iodine Laser (COIL) by pre-dissociation of molecular iodine using a microwave discharge was demonstrated. Two types of approach, transonic operation with grid nozzle and supersonic mixing with ramp nozzle array were tested. In the transonic operation case, a gas velocity at the laser cavity was estimated to be 167 m/s, and I2 dissociation rate was found to be 50%. As a result, 9% of output power enhancement with the microwave pre-dissociation was obtained. In the supersonic injection case, we have initially obtained very poor output power. When we changed the gas flow rates, cavity flow returned to subsonic and we have obtained 284 W output power with 16% of chemical efficiency. No output power enhancement with microwave adoption was observed for ramp nozzle array. It was due to the insufficient dissociation of iodine due to the high stagnation pressure of secondary flow.
Development of Chemical Oxygen-Iodine Laser (COIL) in Tokai University is described. From FY1996, we have conducted a three-year research project sponsored by NEDO (New Energy and industrial technology Development Organization), and it was finished in March 1999. As a result, high-efficiency operation (23.4%) of COIL with nitrogen as a buffer gas was demonstrated. Reduction of the vacuum pump size by the high- pressure subsonic mode operation with turbo blower was demonstrated. Specific energy reached to 3.5 J/liter. Output power stabilization/modulation technique by the external magnetic field was developed. Twisted Aerosol Singlet Oxygen Generator (TA-SOG) was tested and its performance was compared to liquid-jet SOG. TA-SOG was operated at the internal gas velocity of 85 m/s. Novel unstable resonator was developed with the aid of newly developed FFT code. We are now conducting a one-year project whose goal is a development of a 1 kW-class system capable of one-hour stable operation. Finally, three operation modes of future industrial COIL are proposed.
Conceptual designs of a chemical oxygen-iodine laser (COIL) facility for decommissioning and dismantlement (DD) of nuclear facility is proposed. The requisite output power and beam quality was determined base don our preliminary experiments of nonmetal material processing. Assuming the laser power of 30kW, it is derived that the beam quality of M2 equals 36 required to cut a biological shield wall of a nuclear power plant at a cutting speed of 10mm/min. Then the requisite specification of an optical fiber to deliver the laser is calculated. It turned to be quite extreme, core diameter of 1.7mm and NA equals 0.018. The mass flow and heat balance of proposed facility is calculated based on our recent COIL studies. With the high-pressure subsonic mode, the vacuum pump size is minimized compared to the supersonic operation. Finally, the size of the facility is estimated assuming tow-hour continuous operation. It is revealed that such a system can be packed in five railway containers.
Rock excavation experiment with a 10kW-class CO2 laser was demonstrated as a basic study for field application of high power lasers. Sample rocks used in this experiment as a workpiece were tuff breccia and granite. Effect of assist gases on the excavation rate was surveyed. Oxygen, nitrogen, and air were examined and found not to be useful. It was because the gas flow could not blow the molten rocks off, but only helps to cool in case the hole races certain depth. Excavation rate on both rocks for a various output powers was measured to determine thermal constants inherent to each rock. It was found that the excavation rate resulted in slower, as the hole becomes deeper, because of the deterioration in evacuation efficiency of the molten rock. Thermal parameters of the both rocks were derived from the experimental results. Using simplified thermal balance model, it was estimated that a 50 kW-class mobile laser system has a potential to outperform the conventional mechanical excavation technique.
Iodine molecule was dissociated prior to injection in supersonic Chemical Oxygen-Iodine Laser (COIL). In some cases, output power enhancement was observed. However, the output power was decreased at the optimum titration (iodine/oxygen ratio). A quasi-two dimensional simulation was employed to analyze the effect ofiodine pre-dissociation. It was revealed that the high iodine atom concentration at the plenum is responsible for the power reduction. The method to improve the output power by pre-dissociation is discussed.
KEYWORDS: Resonators, Mirrors, Chemical lasers, Chemical oxygen iodine lasers, Laser resonators, Near field, Optical resonators, Radio propagation, Near field optics, Spherical lenses
Unstable resonator with a stable core was developed for Chemical Oxygen-Iodine Laser (COIL). An optical resonator simulation code was developed to optimize the design parameter of the resonator. “Partially coherent optical field” model was employed to handle with multiple transverse mode oscillation. The resonator was successfully oscillated, and a 14 W output with M2=29 was obtained. Theoretically calculated laser output, near-field pattern, and beam quality was in good agreement with experimental results.
The downsizing of Chemical Oxygen-Iodine Laser (COIL) was achieved by applying a turbo blower to a high gas pressure operation of a subsonic COIL. The size of the vacuum system was a factor of 3 smaller than that of the existing one. The laser output power of 290 W with chemical efficiency of 17.1% was obtained at the Cl2 flow rate of 18.6 mmol/s and the laser cavity pressure of 6 Torr.
Brief history and present status of the industrial COIL (Chemical Oxygen-Iodine Laser) studies in Japan are introduced. Up-to-date experimental results obtained by Tokai University group, including high-power subsonic operation, power stabilization, and theoretical works are presented.
KEYWORDS: Magnetism, Chemical oxygen iodine lasers, Chemical lasers, Zeeman effect, Beam controllers, Laser stabilization, Control systems, Signal detection, Servomechanisms, Power supplies
Laser power control of chemical oxygen-iodine laser based on the servomechanism was demonstrated with a Zeeman effect. Response of the feedback system in frequency domain was analyzed and compared to the experimental results. With this feedback system, fluctuation of the laser power was successfully reduced to plus or minus 0.4% in the presence of a disturbance.
KEYWORDS: Oxygen, Chemical lasers, Resonators, Chemical oxygen iodine lasers, Nitrogen, Chlorine, Mirrors, Laser applications, System on a chip, Industrial chemicals
A new concept of energy network system, `optical power system', was proposed. In this system, optical power is generated at a laser facility and it is distributed to users through optical fiber such as electric power system. The authors have started a feasibility study of this concept based on the latest chemical oxygen-iodine laser technology. 23.4% of chemical efficiency was obtained using nitrogen as buffer gas. Buffer gas cooling remarkably increased chemical efficiency. Liquid-jet type singlet oxygen generator (SOG) and twisted aerosol SOG (TA-SOG) were compared with the same setup. TA-SOG showed good performance especially in the high gas flow velocity range.
KEYWORDS: Iodine, Amplifiers, Oxygen, iodine lasers, Chemical species, Chemical lasers, Energy transfer, Signal attenuation, Pulsed laser operation, Continuous wave operation
The feasibility of a 100 kJ class chemically pumped iodine laser amplifier is studied by numerical calculations of the Maxwell-Bloch equations. The idea is based on a chemical iodine pulse laser utilizing a porous-pipe, high-pressure singlet oxygen generator. It is shown that at the high singlet oxygen pressure conditions, the energy transfer reaction from singlet oxygen to ground state iodine atom directly deposits energy on the pulse amplified. Therefore, it is possible to operate an amplifier with low iodine concentration, which ensures the slow deactivation of the stored energy sufficient to fill up a cell of 80 cm in diameter.
Intense red emission was observed occasionally when a pulsed chemical oxygen-iodine laser was operated. The intensity of this emission was at least 100 times higher than any known emission of the oxygen-iodine system. The time history of the emission intensity indicated that it was pumped by the iodine laser. It seemed to be that the rust of the iodine injector was closely related to this emission. The decay time of the emission was measured to be 2 to 4 ms. The spectroscopic measurement revealed that the emission was identical with one that was found by Yoshida et al. and is being studied widely for a new candidate of a visible chemical laser.
A high-pressure pulsed chemical oxygen generator which yields higher than 30Torr of 02(a1?g) is developed. On typical operational conditions, O2(a1?g) pressure rises up to 34Torr in the first 20ms, followed by the slower decay. A simple model calculation showed good agreement with experimental results. The feasibility of the lasing action between O2(a1?g) and O2(X3?g-) was discussed based on this model calculation.
KEYWORDS: Oxygen, High power lasers, Gas lasers, Chemical lasers, Luminescence, Laminated object manufacturing, Chemical analysis, Amplifiers, Iodine, Germanium
A high-pressure pulsed chemical singlet oxygen generator is developed. Obtained maximum singlet oxygen pressure is 20 torr, and excitation efficiency in that moment is crudely estimated to be 40 percent. Experimental results are compared with numerical calculation. Two applications of this generator are presented along with brief evaluation of specifications.
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