In a large-bore copper vapor laser (CVL), excessive gas heating at the axial region of the discharge lowers its efficiency by thermally populating the metastable lower laser levels. The associated lower gas density also lengthens the discharge field- diffusion time, leading to weaker axial pumping and undesired beam characteristics. A novel approach to circumvent this obstacle has been developed by cooling the plasma radiatively via a series of segmented metal plates (septa) placed vertically along the length of the tube. This improved tube design significantly lowers the average gas temperature and shortens the radial delay. A 27% increase in laser power was observed with the addition of septa. We have characterized the beam intensity profile, spatial and temporal pulse variation, and beam polarization through extensive laboratory measurements. A detailed computational model of the laser has been used to characterize and interpret the laboratory results.
A maximum output power of 13.2 W was obtained at a high repetition frequency of 5 kHz by a transversely-excited copper vapor laser with an excited volume of 112 cm3. Its specific output power density was 118 mW/cm3. It corresponded to a specific output energy density of 24 (mu) J/cm3. We also examined the dependence of the output power on the buffer gas pressure, the repetition frequency, and the charging voltage.
Since copper vapor lasers were first reported in 1966, they have suffered from discharge contamination due to outgassing of materials at high temperatures. To remove impurities, a flowing buffer gas is normally used, making a vacuum and gas handling system necessary. A sealed copper vapor laser tube has been developed. Made from metal, glass and ceramic, it features permanent hard seals at electrodes and windows, making the tube rugged and allowing long shelf and operating lives. The first tube in the series, the XL7000, is still on life test and has reached over 1200 operating hours with many thermal cycles.
Using a TE-CO2 laser, we could obtain a long-pulsed laser beam of low initial spike by controlling the discharge current by a pulse forming network and optimizing the gas composition, discharge length to resonator length ratio, and output mirror reflectivity. The maximum laser output was 1.1 J; the initial spike energy, 100 kW; the tail output, 56 kW; and the 16 (mu) sec (FWHM). The maximum repetition rate was 500 Hz. A new type of circuit with small pre-ionization current made it possible to operate the laser at a high repetition rate so as to prolong the laser life. When a 5-inch lens was used, the laser power density at the focal point was 1*108 W/cm2, making it possible to use the laser with an unusually high energy density without causing the breakdown of air insulation. In fact, we succeeded in fine- cutting a 0.5 mm thick alumina ceramic with the laser. It was found that unlike other working methods, the newly developed laser does not cause cracks in ceramic work pieces.
The excited copper vapor distribution within the discharge tube was determined by simulating ASE intensity distribution--obtained with the copper bromide vapor laser equipment--using ASE intensity distribution simulation code. Upper and lower level population of copper vapor were assumed to have a uniform distribution along the tube axis and a Gaussian distribution along the tube radius in this simulation code. The simulation has revealed that distributions concentrate to the center of discharging and the difference of populations between the upper and lower levels little depend on reservoir temperature.
The transverse profiles and evolution of the laser intensities of a high-power copper HyBrID laser (510.6 nm, 578.2 nm) are presented. Both the radial profiles and temporal evolutions of the laser pulse intensities are markedly different in a large- bore (6 cm) HyBrID laser than in conventional elemental metal copper vapor lasers of similar dimensions. The differences in laser intensity distributions and their temporal evolution are attributed to the electron-attaching properties of hydrogen and bromine in the laser buffer gas mixture of a HyBrID laser. The significantly low conductivity of the gas in a HyBrID laser means that the plasma skin effect is relatively weak and does not influence the development of laser oscillation to any great extent; oscillation in a 6 cm bore HyBrID laser begins on the tube axis first and at the wall 3-4 ns later; the time-averaged laser intensity peaks on the tube axis.
The shock waves generated by an excitation discharge on XeCl- excimer laser have been visualized by a shadowgraph technique. The propagation velocity of the shock waves has been measured by using an image converter camera. The propagation velocity is estimated to be approximately 530 m/s for the shock wave beating between the main electrodes, which persists for a long period between the discharge region. On the other hand, the shock wave propagating along the flow axis, which originates from the boundary between the heated column and non-heated region, propagates initially with the velocity of approximately 730 m/s. It is clearly explained by using a plane blast wave theory that the propagation velocity of this shock wave slightly decreases as the shock wave propagates.
A compact (approximately 1 m2 of table space), surface- discharge pumped laser head has been developed and applied to pumping the XeF (C yields A) transition that lases in the blue- green (approximately 485 nm). Having an active length of approximately 50 cm, this device requires no external high voltage or current switches, and presently dissipates > 8 MW per cm of surface discharge. With 5% output coupling (unoptimized), pulse energies > 50 mJ are obtained from the C yields A laser.
Copper vapor and copper halide lasers are the most efficient high-power lasers that operate directly in the visible spectral region. In order to scale these lasers to high average powers, it is important to determine the maximum output power that can be generated from a given volume of the active medium, and the discharge conditions for which it can be achieved. In this paper we describe the attainment of a record average specific output power for self-terminating atomic copper lasers of any type. We have performed our experiments with a narrow-bore (4.5 mm) copper bromide laser. From the active volume of 4.77 cm3 a maximum average output power of 6.7 W was reached, which corresponds to the record specific average power of 1.4 W/cm3. The discharge was excited with a pulse recurrence frequency of 52 kHz. The tube was sealed with pressure of 20 torr neon, to which was added 0.3 torr of hydrogen. We describe the design and construction of the laser tube, the excitation circuit and the discharge conditions which allowed these results to be obtained.
A compact, wavelength agile laser and sensor have been developed for remote detection of chemicals. The laser is a computer- controlled, sealed TEA CO2 device with internal catalyst that operates at a maximum firing and wavelength shift rate of 200 Hz with 40% duty cycle. The wavelength shifter, composed of a fixed grating and galvanometer-mounted mirror, operates in repeating patterns with access to 55 lines in the CO2 spectrum in any order. Multi-mode output energy exceeds 125 mJ for all lines and the output pulse is composed of a 120 nsec wide gain-switched spike, followed by a 1.5 microsecond(s) ec tail. Environmental testing was successfully carried out under a 3 g shock, 2 g sine wave vibration, and a 0-40 degree(s)C temperature range. An operational lifetime exceeding 50 million shots was demonstrated with tests terminated by the operator, not a malfunction. The fully integrated laser weighs 100 pounds and requires only a source of 28 Vdc to operate. The laser was integrated with a sensor and in successful field trials the sensor noise was found to be 1-2%, measurement of atmospheric water vapor was within the accuracy of meteorological instruments; and measurement of concentration-path length product for chemicals in a vapor chamber approached the value expected for the noise figure.
The parametric study has been performed to improve the output performance and the beam properties of a fast axial flow, radio frequency (rf) discharge excited CO laser, where an emphasis is placed on the optimization of an electrode configuration. The laser has a single discharge section which consists of a quartz tube and a pair of cylindrical outer metallic electrodes. The measurements have shown that the discharge uniformity is considerably influenced by the curvature radius of the outer metallic electrodes and the air gap spacing between the tube outer wall and the metallic electrode inner surface at the downstream edge of the electrodes. In the experiments, the most uniform discharge over the tube cross-section has been obtained for a metallic electrode curvature radius of 16 mm and an air gap spacing 0.5 mm. As a result, a maximum specific output obtained has reached 1200 W/m at an entrance gas temperature of 140 K, a corresponding rf to optical conversion efficiency being 21.2%. Furthermore, we have also succeeded in efficient room temperature operation with Xe-free mixtures.
A transversely excited atmospheric (TEA) CO2 laser with gas internal coaxial circulation scheme is presented. To ensure stable discharge the free potential plate UV corona preionization technique is employed. The gas flow velocity reaches 15 meters per second, when the motor rotates at 8000 turns per minute. The TEA CO2 laser is able to operate at 33Hz with more than 106 arcing-free discharge. The minimum clear ratio is found smaller than theoretical limit (root)3.
An investigation and optimization of a single channel transverse RF excited CW sealed CO2 waveguide laser is presented. The laser performance has been studied as a function of various parameters like the excitation frequency, gas pressure, gas mixture composition, and cooling temperature for two pairs of metal electrodes with equivalent sizes, but made of different material - gold plated copper and aluminum. The waveguide structure used was metal-ceramic with an active discharge volume of 2.5X2.5X370 mm3. Single-pass small-signal gain measurements for the two sets of electrodes have been performed, as well. The experiments show that the influence of the electrode material on the laser behavior is significant, while it was generally accepted as a factor of no importance. The best result we obtained with the Al electrodes was a specific output power of 0.78 W/cm with an efficiency of 11% at 125 MHz excitation frequency and 140 Torr of 1:1:5+5% (CO2:N2:He+Xe) gas mixture, which is very close to the highest specific power of 0.85 W/cm, previously reported. With the gold plated electrodes a specific output power of 1.1 W/cm with an efficiency of about 13% was achieved at 190 MHz and 100 Torr 1:1:5+5% gas mixture. This improvement is most likely related to the catalytic properties of the gold layers. This favorable process is accelerated at elevated temperatures, so that an intensive cooling is not necessary for good laser performance. The gain measurements confirmed this behavior. With gold plated electrodes at certain experimental conditions an increase of the gain of a factor 2 was observed.
A transverse RF excited gas discharge has been successfully used to produce a CW Ar-He-Xe laser. A maximum output power of 330 mW has been obtained from an experimental device with 37 cm active length and a 2.25 (DOT) 2.25 cm2 cross-section. This corresponds to a specific output power of about 175 mW/cm3. Under these preliminary optimum conditions the gas pressure was 85 Torr (Ar:He:Xeequals59:40:1). The laser output spectrum consisted of 5 atomic xenon lines (2.03, 2.63, 2.65, 3.37 and 3.51 micrometers ). The 2.03 micrometers and 2.65 micrometers lines were the strongest ones. Complementary to this device a quartz capillary was tested as laser tube for the atomic Xe laser. With this configuration it was possible to sustain a longitudinal DC as well as a transversal RF discharge in the laser gas mixture. Combined excitation was also possible for this device. This enabled us to compare the laser performance in both the DC and the RF mode in the same device. Preliminary measurements showed us that the highest output power in the DC mode was less than 1 mW, while the RF excited laser yielded about 130 mW. The gain coefficient was found to be extremely high. Laser generation was obtained for a wide range of reflectivities R of the outcoupling mirror. At the minimum reflectivity of 5% an output power of 20 mW was obtained. Results obtained from both systems are discussed.
The TEA CO2 laser has many advantages. The multidischarge regions are arranged in its optical cavity. It produces multioptical pulses and the interval time between these pulses may be adjusted. Its structure is simple, and it can be operated without gas flow. However, how to obtain the stable output of multioptical pulses concerns many scientists. In the present paper, the measurements and experimental technologies for raising the output stability of multi-optical pulses is studied.
In this paper, the dynamical behaviors of the class D lasers with modulated term are investigated numerically. The result shows that there exists the so-called generalized bistability in the period-doubling bifurcations, and the two stable states possess space reflected symmetry.
A study of RF discharge for CO2 lasers is made on the basis of RF discharge theory. The relation among dimension of potential fall area, excitation frequency, gas pressure and other parameters is given. The relation among dimension of central dim area, excitation frequency and other parameters is given as well. The study shows dimension of potential area to contract with increasing excitation frequency and gas pressure; dimension of central dim area increases when excitation frequency and gas pressure increases. These results are consistent with experimental results. In the first type of RF discharge, the central dim area is not plasma. In the second type of RF discharge, the central bright area is plasma.
In the previous reports, investigations of DC discharge, pulsed discharge were described and RF discharge pumped frequency of Xenon laser is about 20MHz-30MHz. In this paper we report more high frequency pumping laser 3.508µ radiation in neutral Xenon using a transversely excited pure Xenon and helium-Xenon discharge. The discharge constructure is 1). the glass discharge tube is put in the stripline and 2). the matel parallel electrodes is made discharge tube. The discharge is excited traveling wave with 200MHz-1000MHz. The result of experiment indicate that satisfactory frequency is 200MHz-460MHz for glass discharge tube and about 640MHz for matel parallel electrodes. We also observed that product of pressure with input power as maximum output laser power is constant and relative efficiency no charge for pure Xe lasers in matel parallel electrodes. We had measured 9923 angstrom spontaneous radiation by OMA-III as the frequency of excited discharge is changed. Since the transitions originates on the lower laser level. It's intensity relates to laser radiation.
The Los Alamos advanced FEL has been built specifically for industrial and research applications. Advanced technologies such as a high-brightness photoinjector, a high-gradient compact linac, and permanent magnet components reduce the Advanced FEL size and yet maintain its high-average-power capability. The Advanced FEL has been in operation in the near IR since (4 to 6 micrometers since early 1993. Recent results of the Advanced FEL lasing characteristics and high-average-power upgrades are presented.
Electrostatic-accelerator free-electron lasers (EAFELs) are used to generate intense, CW, single-mode, laser radiation for space power beaming applications such as envisioned by the project SELENE. Using present electrostatic accelerator technology (<EQ MV), together with the electron gun and electron collector technology developed for the UC Santa Barbara FEL we discuss several laser configurations. The first one entails using a single 25 MV, 2 A, DC electron beam system to produce 100 kW power at 1.54 micrometers . At the same wavelength and with the same accelerator the power can be increased up to 3.1 MW using a 20 A electron gun. Still, with the same type of accelerator but with higher currents, 0.84 micrometers can be generated. A third configuration discussed in this paper requires two high voltage accelerators to reach electron energies of up to 50 MV. The major advantage of using EAFELs is that true CW, single-mode operation can be achieved with a minimum expected wall power efficiency of 25%. We also discuss ways to produce 10 MW average power, that would require additional technology developments.
A possible approach to high efficiency FEL operation is to combine a microwave linear accelerator and magnetic wiggler into a single structure. As the electrons lose energy to the radiation at the FEL oscillation wavelength (e.g. 10 micrometers ), energy is replaced by the microwave linac. The electron beam acts as a catalyst for the conversion of microwave power to infrared power. Several advantages to the accelerator/wiggler are: it is possible to obtain high conversion efficiency in a short length; small- signal gain reduction can be avoided; power extraction may be increased by increasing length; there is little detrapping; and electron beam energy out of the wiggler is relatively monochromatic, permitting efficient energy recovery. The expected performance of the high efficiency FEL will be calculated by computer simulation based on parameters measured on a full scale, six period model. The gain and efficiency will be estimated with and without the presence of the accelerating microwave field. Simulation results predict an efficiency greater than 15% in a 135 m long accelerator/wiggler. A fast (< 1 microsecond(s) time constant) variable attenuator will be used to modulate the microwave field in time so that small signal gain reduction is avoided. The optimum value of microwave field as a function of time will be calculated and the sensitivity of the gain to the microwave field will be discussed.
Laser power beaming of energy through the atmosphere to a satellite can extend its lifetime by maintaining the satellite batteries in operating condition. An alternate propulsion system utilizing power beaming will also significantly reduce the initial insertion cost of these satellites, which now are as high as $DLR72,000/lb for geosynchronous orbit. Elements of the power beaming system are a high-power laser, a large diameter telescope to reduce diffractive losses, an adaptive optic beam conditioning system and possibly a balloon or aerostat carrying a large mirror to redirect the laser beam to low earth orbit satellites after it has traversed most of the earth's atmosphere vertically. China Lake, California has excellent seeing, averages 260 cloud-free days/year, has the second largest geothermal plant in the United States nearby for power, groundwater from the lake for cooling water, and is at the center of one of the largest restricted airspaces in the United States. It is an ideal site for such a laser power beaming system. Technological challenges in building such a system and installing it at China Lake will be discussed.
Simulations in two transverse spatial dimensions and time are used to study the evolution of the optical mode in a free electron laser. It is assumed that the electron beam is narrow, the current is low, and the optical fields are weak. Over a single pass, optical mode distortion results in increased gain as the electron beam radius decreases while total current is held constant. Over many passes with transmission and diffraction losses included, the optical mode is still distorted, but the trend of increasing gain is no longer observed.
The Stanford Linear Accelerator Center (SLAC) linac has been proposed as an electron beam source for a high power X ray FEL. Compressing the electron pulse to a sub-picosecond length yields a peak current of 2500 amps. An electron beam energy of 7 GeV would result in a radiation wavelength of 4 nm and peak optical power in the gigawatt range. In order to examine this proposal, single-mode phase space simulations are run to look at the effectiveness of electron bunching and the onset of saturation. A longitudinal multimode simulation shows coherence development and the trapped-particle instability. Transverse multimode simulations examine the effects of optical guiding and mode distortion.
SELENE (SpacE Laser ENErgy) is a proposal to use a free electron laser (FEL) as a ground-based power source for several space applications. An advanced FEL utilizing a multisection optical klystron coupled to a single pass radiator has been suggested. Phase space simulations show electron bunching at low optical power in the klystron oscillator, leading to high gain in the single pass radiator.
In this paper the undulator brightness and central wavelength expressions of a longitudinal wiggler magnetic field are discussed. A relativistic electron beam possessing finite perpendicular momentum introduces several transverse harmonics of motion while travelling through a longitudinally polarized wiggler magnetic field. These harmonics modulate the longitudinal electron velocity and as a consequence the radiation spectrum exhibits several harmonics.
A facility to generate high-intensity, ultrashort pulses of broad-band far-infrared radiation has been assembled and tested at Stanford. The device uses sub-picosecond relativistic electron bunches to generate coherent radiation through transition or synchrotron radiation in the far-infrared (FIR) regime between millimeter waves and wavelengths of about 100 micrometers and less. Experimental results show a peak radiation power of greater than 0.33 MW within a microbunch and an average FIR radiation power of 4mW. The average bunch length of 2856 microbunches within a 1 microsecond(s) ec macropulse is estimated to be about 480 fsec. Simulations, experimental setup and results will be discussed.
Machining characteristics of Fiber Reinforced Plastics (FRPs) using excimer laser have been examined at three wavelengths 193 (ArF), 248 (KrF), and 308 (XeCl) nm in the fluence ranges up to 80 J/cm2. At 308 nm, a maximum removal rate was measured to be as high as 15 micrometers /pulse for the plastics with glass fiber and epoxy matrix (glass/epoxy). Irrespective of fibers and matrix materials, removal rates increased with applying a longer laser wavelength. Complementary studies were also conducted on glass/epoxy at 308 nm to examine the effect of purge gases (He, N2, Ar) to the irradiated area. It was found that Ar and N2 were effective for improvement of the kerf quality and reduction of sooty debris around the irradiated area.
Laser technology has found its new application in the gravure printing industry. The argon gas laser is used as a light source. The beam is controlled by a graphic software and used to expose a printing cylinder coated with photosensitive material. After the chemical process, the artwork is thus etched onto the cylinder and ready to reproduce pages. The laser exposure process, and the cylinder engraving processes will also be discussed. The samples of laser exposed images will be presented.
Theoretical description of different collisional dephasing processes in molecular and atomic gases is presented. Experimental data, obtained by time-domain CARS spectroscopy method for thulium vapors, are analyzed on the basis of the presented theory. Physical parameters of investigated atoms are obtained.
The action of CO2 laser (power density of 103 - 106 W/cm2) on silicates has been investigated. Spectroscopic and chemical analysis of sublimates and irradiated zone made it possible to establish that by laser action on these matters the selective excitation of localized vibrational mode up to breaking of covalent bonds with the selective sublimation of Si-0 groups take place.
Results of experiments on gas-laser cutting of composition glasses three ply using emission of an electric discharge close circuit subsonic CO laser are presented. The parameters of the experimental arrangement are given. It is shown that satisfactory results for division of three ply glass with thickness about 7 mm are obtained when the rate of stretching is 2 m/min and output power is 400 W.