Abstract: The invention provides a laser medium having improved photodynamical properties. The medium includes the condensed phase, namely solid or liquid phase, of a mixture of one or more rare gases and a halogen donor. The gases are first combined and then condensed to form the laser medium. A solid state rare gas crystal laser is also provided.

Abstract: Apparatus for controlled ablation of material from a predetermined working point, comprising a first laser, in particular excimer laser, for generating laser radiation pulses having a wavelength in a wavelength range suitable for the ablation, in particular in the ultraviolet spectral range, further comprising a radiation analyzer such as a spectrometer for analysis of material-specific radiation from the ablation plume forming at the working point, and a second laser, in particular a tunable dye laser, for generating a further laser radiation in a wavelength range which is different from said first wavelength range and which is better suited for the resonant stimulation of the radiation serving for the analysis than the ablation radiation wavelength range.

Abstract: An apparatus for controlling an output from an excimer laser device wherein at least two etalons each having a large diameter are arranged between a rear mirror and a laser chamber for the excimer laser device is disclosed. With the apparatus, the operative range of laser light outputted from the excimer laser device can be narrowed by executing superposition control for a wavelength of laser light which transmits through each etalon, while maintaining the number of spatial lateral modes. The apparatus is preferably employable as a light source particularly for a unit for projecting and exposing figures in a reduced size. Superposition control with the use of a superposition control unit, excitation intensity control for laser gas with the use of an excitation intensity control unit and partial gas replacement control for laser gas with the use of a gas control unit are executed in a predetermined timing relationship, respectively.

Abstract: An excimer laser has a pair of main electrodes defining a lasing space, and a series of pairs of pre-ionization pins arranged alongside the main electrodes. These pins form preionization gaps for generating discharges that provide ultraviolet radiation to condition the gas in the lasing space. The invention consists of providing a tracker of insulating material between each pair of pins to bridge the gap and provide a tracking surface for the pre-ionization discharge.

Abstract: Discharge tubes formed of metal fluoride gases are used in apparatus for emitting high frequency laser and fluorescent light. The discharge tubes are resistant to corrosion from halogen-containing gas mixtures subjected to high frequency excitation in the apparatus.

Abstract: A compact excimer laser, including a housing structure having a plurality of walls forming an internal laser cavity. A gas is located within the laser cavity and with the gas capable of lasing action. A pair of spaced electrodes are located within the laser cavity and form an electrical discharge area between the electrodes for stimulating gas within the discharge area to lasing action in accordance with an electrical discharge between the electrodes. One of the pair of electrodes is located along a central position within the cavity and is grounded to the housing structure. The other of the pair of electrodes is located adjacent to but spaced from one of the walls of the housing structure and with the other electrode mounted on a main insulator member.

Abstract: A compact excimer laser, including a housing structure having a plurality of walls forming an internal laser cavity. A gas is located within the laser cavity and with the gas capable of lasing action. A pair of spaced electrodes are located within the laser cavity and form an electrical discharge area between the electrodes for stimulating gas within the discharge area to lasing action in accordance with an electrical discharge between the electrodes. One of the pair of electrodes is located along a central position within the cavity and is grounded to the housing structure. The other of the pair of electrodes is located adjacent to but spaced from one of the walls of the housing structure an with the other electrode mounted on a main insulator member.

Abstract: A compact excimer laser, including a housing structure having a plurality of walls forming an internal laser cavity. A gas is located within the laser cavity and with the gas capable of lasing action. A pair of spaced electrodes are located within the laser cavity and form an electrical discharge area between the electrodes for stimulating gas within the discharge area to lasing action in accordance with an electrical discharge between the electrodes. One of the pair of electrodes is located along a central position within the cavity and is grounded to the housing structure. The other of the pair of electrodes is located adjacent to but spaced from one of the walls of the housing structure and with the other electrode mounted on a main insulator member.

Abstract: A compact excimer laser, including a housing structure having a plurality of walls forming an internal laser cavity. A gas is located within the laser cavity and with the gas capable of lasing action. A pair of spaced electrodes are located within the laser cavity and form an electrical discharge area between the electrodes for stimulating gas within the discharge area to lasing action in accordance with an electrical discharge between the electrodes. One of the pair of electrodes is located along a central position within the cavity and is grounded to the housing structure. The other of the pair of electrodes is located adjacent to but spaced from one of the walls of the housing structure and with the other electrode mounted on a main insulator member.

Abstract: A compact excimer laser, including a housing structure having a plurality of walls forming an internal laser cavity. A gas is located within the laser cavity and with the gas capable of lasing action. A pair of spaced electrodes are located within the laser cavity and form an electrical discharge area between the electrodes for stimulating gas within the discharge area to lasing action in accordance with an electrical discharge between the electrodes. One of the pair of electrodes is located along a central position within the cavity and is grounded to the housing structure. The other of the pair of electrodes is located adjacent to but spaced from one of the walls of the housing structure and with the other electrode mounted on a main insulator member. The main insulator member is formed of ceramic material and is located intermediate to the one wall of the housing and the other electrode but is spaced from the one wall of the housing to have the main insulator member floating relative the housing structure.

Abstract: A pulsed beam from an excimer laser is used for precision ablation of cadmium telluride (CdTe) and other materials to fabricate and delineate devices in electronic microcircuit structures. The fluence of the beam may be adjusted to selectively remove one constituent of the material, such as cadmium vs. tellurium, at a higher rate than the other constituent, while maintaining the integrity of the material surface. The beam may selectively remove an epitaxial layer of CdTe, CdZnTe, or HgCdTe from a GaAs substrate. The beam may be directed through a projection mask and optical system onto a material to form an image for patterned ablation. The optical system may focus an image of the mask on the material to form vertical sidewall patterns, or slightly defocus the image to form curved sidewall patterns and/or concave and convex lens structures for optical arrays.

Abstract: A compact excimer laser, including a housing structure having a plurality of walls forming an internal laser cavity. A gas is located within the laser cavity and with the gas capable of lasing action. A pair of spaced electrodes are located within the laser cavity and form an electrical discharge area between the electrodes for stimulating gas within the discharge area to lasing action in accordance with an electrical discharge between the electrodes. One of the pair of electrodes is located along a central position within the cavity and is grounded to the housing structure. The other of the pair of electrodes is located adjacent to but spaced from one of the walls of the housing structure and with the other electrode mounted on a main insulator member.

Abstract: A compact excimer laser, including a housing structure having a plurality of walls forming an internal laser cavity. A gas is located within the laser cavity and with the gas capable of lasing action. A pair of spaced electrodes are located within the laser cavity and form an electrical discharge area between the electrodes for stimulating gas within the discharge area to lasing action in accordance with an electrical discharge between the electrodes. One of the pair of electrodes is located along a central position within the cavity and is grounded to the housing structure. The other of the pair of electrodes is located adjacent to but spaced from one of the walls of the housing structure and with the other electrode mounted on a main insulator member.

Abstract: A gas control device in a halogen gas laser device which comprises: a filter for receiving a small quantity of deteriorated gas from the upstream portion of the laser gas circulating path to convert it into a low-boiling-point gas; and a gas detector for measuring the density of the low-boiling-point gas thus formed, to estimate the halogen gas density, and outputting, when the density is lower than a predetermined value, an instruction signal to supply halogen gas.

Abstract: A fiber optic device for remote delivery of intense ultraviolet optical signals comprising an excimer laser source and an optical fiber. The output of the pulsed, transverse discharge, high pressure laser source is coupled to an articulating reflection mechanism which directs the pulsed laser output to an input end of the optical fiber. The optical fiber serves to transmit the light from the laser source to a remote location or target. The excimer laser further comprises a segmented first elongated laser electrode and a coextensive second laser electrode which is substantially solid. The discharge is stabilized by inductors connected to each segment of the first electrode and further by preionization electrodes located adjacent and coextensive with the second electrode. The preionization electrodes comprise a central conductor surrounded by a dielectric sleeve. The laser further comprises a closed gas system for the lasing medium gas.

Abstract: A method and apparatus for cleaning the optical elements in an excimer laser in situ. A source of high pressure carbon dioxide gas is allowed to escape through a nozzle facing the surface of the optical elements. The escaping gas expands and cools sufficiently to form a carbon dioxide ice jet. The ice jet strikes the surface of the optical elements causing cleaning of the elements by abrasion. Carbon dioxide may be removed merely by evacuation and purging of the system. Thus the mirrors are cleaned without removing them.

Abstract: A laser apparatus includes an optical resonator having a laser medium and generating a laser light. A wavelength selection element selects a given wavelength of the laser light. The selected wavelength resides within a gain bandwidth of the laser medium. A sealed container houses the wavelength selection element. The sealed container may be filled with a gas. A density of the gas within the sealed container may be changed to vary the selected wavelength.

Abstract: A laser apparatus comprises an optical resonator including first and second mirrors, and lasing medium. An wavelength selection element is provided in the resonator for narrowing band-width. A polarizing conversion element for changing ratio of S to P components and polarizing beam splitter are provided for amplifying laser beam to output after wavelength selection and for reducing light load of the wavelength selection element. The polarizing conversion element is provided in the resonator light path. In another embodiment, the polarizing conversion element is provided in a branch light path formed by a second polarizing conversion element and a third mirror, where the second polarizing conversion element reflects and transmits P component at a given ratio and reflects S component. The wavelength selection element comprises a Fabry-Perot etalon, grating, or prism. The polarizing conversion element comprises a quarter-wave plate or a phase retarder mirror.

Abstract: A spectrometer is disclosed, in which plural entrance slits are mounted, and a reference light passing through one entrance slit and the light to be measured passing through the other entrance slit are simultaneously focused on a photo-sensitive surface of a detector through a diffraction grating and a focusing optical system, to measure the wavelength of the light to be measured precisely by using the reference light as a standard.

Abstract: An ignitor for a preionizing means of an excimer laser has an electrically conductive core which projects into the gas space of the laser and which is surrounded by a jacket of a fluoroplastic. The jacket is brought into sealing engagement with the wall of the laser gas space by means of a pressure sleeve via mating conical surfaces.

Abstract: A system and method for the purification of laser gases having impurities therein. The pressure on the liquid nitrogen in a Dewar vessel controls the boiling point of the liquid nitrogen. The laser gas to be purified flows into heat exchange relationship with the liquid nitrogen at a temperature above the liquification temperature of the laser gas but below the liquification temperature of the impurities. The impurities are precipitated and removed and the laser gas recycled for further use.

Abstract: In a vacuum laser irradiating apparatus disposed between a laser generator and a vacuum vessel in which an object to be irradiated with a laser beam is placed, an outer window plate is airtightly fixed to the outer opening of the apparatus body to maintain the internal cavity of the apparatus body under a vacuum and to pass the laser beam therethrough. This outer window plate is reinforced so as not to be distorted due to pressure difference between an inside vacuum of the apparatus body and an outside atmospheric pressure. This is because the outer window plate is made of an expensive pure monocrystalline material and therefore it is preferably to reduce the thickness thereof for material cost reduction.

Abstract: An excimer laser including a discharge chamber containing a mixture of halogen, rare gas and buffer gas uses two gas sources to replenish the halogen in the discharge chamber while maintaining the concentrations of all the gases at the optimum levels. One of the gas sources, source A, contains a mixture of the rare gas and the buffer gas in optimum concentrations. The other gas source, source B, contains both the rare gas and the buffer gas, in optimum relative concentrations, and also the halogen, in a concentration which is greater than optimum. As the laser operates and the gain of the laser decreases due to halogen depletion, gas from source B is injected into the discharge chamber to raise the halogen concentration. Gas is then released from the chamber to reduce the chamber pressure to the original level.

Abstract: A laser gas used in a rare gas fluoride excimer laser is efficiently refined with little loss of the principal rare gas such as Ar, Kr or Xe by sequential contact of the laser gas first with a reactive metal, e.g. Si or Fe, for conversion of the fluorine source gas such as F.sub.2 or NF.sub.3 to a metal fluoride, then with a solid alkaline compound, e.g. Ca(OH).sub.2, for conversion of gaseous fluorides to solid metal fluorides, next with zeolite which is adsorbent of most of the remaining impurities and finally with an alkaline metal, e.g. Ca or Na, for decomposition of CF.sub.4 to form a solid metal fluoride and carbon. CF.sub.4 is formed during operation of the excimer laser by reaction of fluorine with a fluororesin used as electrical insulator in the laser apparatus, and accumulation of CF.sub.4 in the laser gas caused significal lowering of the laser output power.

Abstract: A compact excimer laser, including a housing structure having a plurality of walls forming an internal laser cavity. A gas is located within the laser cavity and with the gas capable of lasing action. A pair of spaced electrodes are located within the laser cavity and form an electrical discharge area between the electrodes for stimulating gas within the discharge area to lasing action in accordance with an electrical discharge between the electrodes. One of the pair of electrodes is located along a central position within the cavity and is grounded to the housing structure. The other of the pair of electrodes is located adjacent to but spaced from one of the walls of the housing structure and with the other electrode mounted on a main insulator member.

Abstract: An excimer laser apparatus with an HCl generator. The HCl generator is constructed so that HCl gas is generated by the reaction of a fixed concentration of hydrogen gas in the laser gas mixture with an equivalent amount of metallic chlorides. The reaction occurs at a preset temperature, and the metallic chlorides may be either in the laser gas chamber or in the circulation line of the laser gas. Consequently, the HCl required for laser generation is continuously formed by the H.sub.2 reduction of the metallic chlorides. The HCl loss due to the formation of impurities is automatically replenished to maintain a constant concentration of HCl in the laser gas, which results in stable laser generation. This simplified and dependable excimer laser apparatus can be operated continuously for a long time, since it is not necessary to measure and replenish the HCl lost due to the formation of impurities. Furthermore, instead of using a bomb for the highly toxic HCl gas, a bomb for He mixed with H.sub.

Abstract: A chemical laser comprising means for producing metal trimers, means for dissociating halogen molecules, a reaction chamber, and means for delivering the metal trimer and halogen atoms into the reaction chamber to form electronically excited metal dimer molecules in sufficient concentration to create a population inversion and laser amplification.

Abstract: An apparatus and method are provided to homogenize the intensity profile of the beam emitted by an excimer laser. The excimer laser beam is collected by a closely packed ultraviolet-grade optical fiber bundle array having its individual fibers intermingled in a random or preconceived format to result in an intermixing of the light from the individual fiber cores to produce a uniform intensity profile. The output ends of the fibers are gathered or fused, and optionally tapered. before being cleaved to provide an output face that is custom shaped for a desired illumination pattern. The flexible nature of the fiber bundle allows for remote materials processing applications.

Abstract: A rare gas-halogen excimer laser in which the laser gases are exposed only to compatible materials that react with the laser gases to produce stable reaction products having a low vapor pressure, so as to reduce contamination of the gases and optics. High-purity nickel is the preferred material for components that are electrically conductive, and high-purity alumina is the preferred material for components that are non-electrically conductive. No non-compatible materials are used. In another feature, magnetic fluid seals are provided for the laser's fan-shaft, to isolate the shaft bearings and thereby isolate any non-compatible lubricant for the bearings. The fan uses magnetic coupling so that an isolating enclosure may be placed over the magnetic fluid seal to prevent the leakage of gases into the surrounding environment if the seal ever fails.

Abstract: The invention relates to a plasma apparatus where plasma is generated utilizing microwave discharge and laser excitation is performed and plasma processing is performed. More specifically, in a plasma apparatus where a microwave from a microwave oscillator is transmitted through a microwave transmission path to a microwave circuit, and plasma is generated by a microwave discharge within the microwave circuit, a plasma generating medium for generating the plasma is filled in a space formed between a conductor wall constituting a part of the microwave circuit and a dielectric installed opposite to the conductor wall, and the microwave circuit forms microwave mode having an electric field component orthogonal to the boundary between the dielectric and the plasma.

Abstract: An excimer laser source system that produce radiation characterized by a wavelength with a high degree of stability and by a narrow spectral bandwidth is described. Such an excimer laser system is suitable as a source in high-resolution high-throughput lithography. Key features of the disclosed system are: frequency-locking of the excimer laser center wavelength to the cavity spacing of a highly stable external Fabry-Perot or other resonator; stabilization of the external resonator by referencing its cavity spacing to a frequency-locked reference laser; stabilization of the reference laser by locking its frequency to a fundamental atomic or molecular transistion; and provision of an intra-cavity or other Fabry-Perot resonator in the excimer laser optical cavity to both narrow the spectral bandwidth of the laser and to select its center wavelength.

Abstract: Apparatus and method for producing laser radiation from an element of a binary (or more complex) compound pumped by microwave energy. The energy causes the compound to dissociate and for the one element of the compound to go to its first excited state, this state being metastable. As the element emits radiation, it reverts to its ground state and recombines to form a compound (which may be the original compound) capable of being dissociated by the microwave energy and repeating the process.

Abstract: A laser therapy system having improved effectiveness in surgical use, particularly in laser angioplasty, can be formed by employing a pulsed source of radiation. The pulsed energy source is preferably an excimer laser having a coherent beam of ultraviolet radiation and preferably is employed in conjunction with a dye laser to produce an output beam which is tunable over a wide portion of the ultraviolet and visible spectrum. The output beam is coupled via a novel coupling device to an optical fiber disposed within a surgical instrument, for example, a percutaneous catheter. The operative components are sealed in a gas-tight, liquid-tight housing. An electronic controller monitors and adjusts the output energy density, duration, and pulse repetition rate. In operation, a pulsed, high energy beam of extremely short duration is available to remove atherosclerotic plague with less damage to the underlying tissue and less chance of perforating the blood vessel wall.

Abstract: An electrode for pulsed gas lasers consisting substantially of tungsten and copper has a long life. With such an electrode contaminations of the laser gas and of the windows are largely obviated, even in long-time operation. An electrode suitable also for fluoride-containing laser gases consists essentially of an alloy containing copper, aluminium and nickel.

Abstract: A reduced projection light source comprises a laser device for emitting laser light having a transverse mode of multimodes, and an etalon located between a chamber of the laser device and a total reflection mirror. The light source is used as an exposure light source for transfer printing an ultrafine pattern on a semiconductor wafer.

Abstract: A reflector for an excimer laser is composed of an aluminum layer deposited on a substrate and at least two pairs of dielectric multilayers of high refractive index material and low refractive index material alternately piled on the aluminum layer, and optical thickness of the respective layers of an outer pair of the dielectric multilayers are deviated from .lambda./4 and total optical thickness of the outer pair is made to be .lambda./2.

Abstract: Process and apparatus for obtaining an excimer and application to a laser.The apparatus comprises a compression chamber (9), compressor (11) for compressing the gaseous mixture R+XY+M in the compression chamber (9), an expansion chamber (3) communicating at least one opening (23,23a) with the compression chamber (9), a vacuum pump (25) for producing within the expansion chamber (3) a pressure well below that prevailing in the compression chamber (9), the pressure difference between the compression and expansion chambers, the surface of the opening and the volume of the compression chamber being such that the gaeous mixture entering the compression chamber undergoes a supersonic adiabatic expansion with a Mach number at least equal to 10 and electrodes (27, 29, 27a, 29a) for producing an electric discharge (E) in the expansion chamber (3), downstream (x) of the opening (23, 23a) FIG. 2.

Abstract: Specification of an etalon included in a multimode, narrow-band oscillation excimer laster used as a light source for light exposure in photolithography are set to satisfy a relation S.lambda.W.lambda.R.lambda. (u,v)d.lambda..gtoreq..alpha., where .alpha. is an optical transfer function necessary for light exposure of resist according to a reticle pattern, R.lambda.(u,v) is an optical transfer function of monochromatic light for an illuminating system and a reduced-projection lens, W.lambda. is a weight which is applied to a waveform of a power spectrum in an oscillation laser beam at a wavelength .lambda.. Further, an inclination angle .lambda. of the etalon in its normal direction with respect to an optical axis when the etalon is provided between the chamber and rear mirror is set to satisfy a relation .theta.>tan.sup.

Abstract: In an excimer laser system with wavelength bandwidth narrowing, a feedback loop for monitoring and correcting the tuning of the laser employs a wavelength calibration device in the form of a gas with an absorption peak at the desired narrow wavelength. A portion of the laser output received through the gas provides the information for generating the correction signal.

Abstract: A transverse electrically excited gas laser comprises a mixture of rare gases and a fluorine donor at selected partial pressures so as to permit UV and/or visible rare gas-halide laser oscillation at two or more wavelengths simultaneously.

Abstract: A microwave pumped excimer laser and method.

Abstract: A solid state laser in which molecules containing transition metal ions form the lasing medium. More particularly, the electronic states of molecular complexes containing transition metal ions, which are in closed shell configurations, are pumped by an ultraviolet source to emit coherent radiation.

Abstract: A rare gas halide laser has a hollow discharge tube disposed between two metal electrodes, and a high frequency electrical generator attached to the electrodes. In order to increase the duty factor of the laser, the bore in the discharge tube is formed with two opposing walls which are separated by a small distance, preferably less than 0.5 millimeters, so that the rate of recombination of the halide compound is increased.

Abstract: A composition of matter is provided which is capable of producing laser energy on being pumped. The composition comprises a first chemical entity and a second chemical entity, wherein the first and second entities form a charge bearing molecule when excited to a relatively higher energy state and exist as distinct non-associated entities when in a relatively lower energy state. A method of producing laser energy and a laser, utilizing such composition of matter, also form a part of the invention. Generally, at least one of the first and second chemical entities in the charge bearing molecule has a number of electrons substantially equal to the number of electrons of a noble gas or of a halogen. A very high energy laser can result.

Abstract: A coherent laser beam having a possibly non-uniform spatial intensity distribution is transformed into an incoherent light beam having a substantially uniform spatial intensity distribution by homogenizing the laser beam with a light tunnel (a transparent light passageway having flat internally reflective side surfaces). It has been determined that when the cross-section of the tunnel is a polygon (as preferred) and the sides of the tunnel are all parallel to the axis of the tunnel (as preferred), the laser light at the exit of the light tunnel (or alternatively at any image plane with respect thereto) will have a substantially uniform intensity distribution and will be incoherent only when the aspect ratio of the tunnel (length divided by width) equals or exceeds the contangent of the input beam divergence angle .theta. and whenW.sub.min =L.sub.coh (R+(1+R.sup.2).sup.1/2)>2RL.sub.coh,where W.sub.min is the minimum required width for the light tunnel, L.sub.

Abstract: A laser gas used in a rare gas halide excimer laser is efficiently refined with little loss of the essential rare gas such as Kr, Ar or Xe by contact of the laser gas with a solid alkaline compound, e.g. Ca(OH).sub.2, for conversion of acidic impurities and also the halogen source gas such as F.sub.2 or HCl into solid metal halides and contact of the remaining gas with zeolite which is adsorbent of the remaining impurities. When the halogen source gas comprises a highly oxidizing fluorine matter the laser gas is first brought into contact with a reactive metal, e.g. Si or Fe, to convert the oxidizing fluorine matter into metal fluorides to thereby prevent formation of O.sub.2, which is obstructive to the laser operation, by reaction of the oxidizing matter with the alkaline compound.

Abstract: For an excimer laser system utilizing in a laser chamber a lasing material and a mixture of a diluent rare gas and a heavy rare gas and halogen rare gas in given percentages, there is disclosed a method and apparatus for reducing the expenditure of the rare gases by continuously evacuating the laser mixture from the laser chamber removing from the evacuated laser mixture any gaseous impurities to provide a cleaned laser mixture and thereafter feeding the cleaned laser mixture back into the laser chamber. Along with the cleaned laser mixture there is fed in a supplemental halogen gas. The gaseous impurities along with the halogen are removed by passing the gas through an elongated tube having calcium particles therein with a void fraction for a given length of tube in the range 0.30 to 0.60. Some of the ratio is obtained by providing alternate layers of calcium particles and inert, refractory spacers, such as stainless steel wool.

Abstract: The present invention relates to excimer laser equipment which is one kind of gas laser, and in particular to a rare gas-halide excimer laser using rare gases and halogens as laser media, and adapted to control the concentration of halogens contained in laser media therewithin on the basis of the result of the measurement of the concentration of halogens in the laser media which is being used for the oscillation of laser rays therein, whereby the stabilized oscillation of the laser is always possible.

Abstract: A pre-excited excimer laser is formed in a thin flat package. Input X-ray photons which are modulated by passing through a body to be analyzed raise the pre-excited excimer gas molecules to a lasing energy level and the coherent radiation produced is measured and produces an amplified image of the input X-ray photon modulation.

Abstract: A method for injection locking a xenon chloride laser at 308.4 nm. Neon (Ne) is used as a diluent in the laser to shift slightly the gain profile of the laser towards the longer wavelengths and towards 308.4 nm. The laser is operated at a lower level of gain than is used in the prior art by using a lower level of electrical discharge than was used in the prior art. The lowered gain reduces the numerical magnitude of the difference in the gain of the laser at 308.4 nm and its gain at the highest gain modes of operation. Either a low level signal at 308.4 nm is injected into the laser to mode lock the lowered gain laser at 308.4 nm. or a frequency selection device such as etalons is inserted within the laser cavity to restrict operation to 308.4 nm. The period of the electrical discharge also is lengthened from that typically used in the prior art so as to obtain saturation of the output at 308.4 nm.