Abstract: A laser resonator comprising a specially designed front mirror 32. The front mirror 32 together with a rear mirror form a resonator cavity. As well as having a resonator cavity reflective surface 42, the front mirror 32 also has an output coupling reflective surface 44 which forms a continuation of the resonator cavity reflective surface 42 and extends at an angle thereto so as to direct a beam laterally out of the cavity. The output coupling reflective surface 44 and the resonator cavity reflective surface 44 are joined by a “soft” rounded edge 40 of arcuate cross-section, this rounded transition suppressing diffraction ripples that would otherwise be generated if the edge were “hard”, i.e. sharp.

Abstract: A light exposer according to an embodiment of the present invention includes an exposure beam generator generating an exposure beam, and a vacuum chamber passing the exposure beam generated by the exposure beam generator and including a first fly eye lens having a plurality of convex lens like fly eyes. The exposure beam generator includes an oscillator including an oscillator pumping chamber, a first prism and a second prism, and a first exposure beam diameter changing lens positioned before the first prism and enlarging a diameter of the exposure beam.

Abstract: A laser system includes a laser resonator having a laser resonator volume and a gain block disposed therein, the gain block being configured to emit light at a predetermined laser wavelength, and an OPO unstable resonator having an OPO unstable resonator volume, the OPO unstable resonator optically coupled to the laser resonator and configured to receive light therefrom, wherein a portion of the OPO unstable resonator volume is situated with respect to the laser resonator volume so as to form an overlapping volume.

Abstract: In one aspect a power amplifier comprises a first plurality of laser disks disposed in a first vertical plane and a second plurality of laser disks disposed in a second vertical plane, opposite the first vertical plane, wherein the plurality of laser disks are disposed in a central horizontal plane, and a first plurality of reflecting mirrors disposed in the first vertical plane and a second plurality of reflecting mirrors disposed in the second vertical plane, wherein a first set of reflecting are disposed in a lower horizontal plane and a second set of reflecting mirrors are disposed in an upper horizontal plane, wherein respective laser disks and reflecting mirrors adjacent along an optical axis are positioned to provide a 1:1 imaging system therebetween. Other aspects may be described.

Abstract: A highly-coherent chip-based laser generating system includes a disk resonator incorporating a wedge structure fabricated from a silicon dioxide layer of a chip. The disk resonator is operable to generate a highly-coherent laser from a low-coherence optical pump input provided at an optical power level as low as 60 ?W. The disk resonator is fabricated with sub-micron cavity size control that allows generation of a highly-coherent laser using a controllable Stimulated Brillouin Scattering process that includes matching of a cavity free-spectral-range to a Brillouin shift frequency in silica. While providing several advantages due to fabrication on a chip, the highly-coherent laser produced by the disk resonator may feature a Schawlow-Townes noise level as low as 0.06 Hz2/Hz (measured with the coherent laser at a power level of about 400 ?W) and a technical noise that is at least 30 dB lower than the low-coherence optical pump input.

Abstract: A thin beam laser crystallization apparatus for selectively melting a film deposited on a substrate is disclosed having a laser source producing a pulsed laser output beam, the source having an oscillator comprising a convex reflector and a piano output coupler; and an optical arrangement focusing the beam in a first axis and spatially expanding the beam in a second axis to produce a line beam for interaction with the film.

Abstract: A method for providing a laser beam and a laser arrangement that includes an elongated tube; an elongated discharge region within the elongated tube including a discharge medium to be excited to induce laser radiation; two DC discharge electrodes disposed at opposite ends of the elongated discharge region; two RF electrodes disposed at opposite elongated sides of the elongated discharge region; and/or a laser resonator having two opposite mirrors disposed at opposite ends of the elongated tube, the laser resonator is unstable in at least one lateral axis. The method includes applying a DC discharge between the DC electrodes, and applying a RF discharge transverse to the DC discharge between the RF electrodes. The DC and RF discharges may be provided by the DC and/or RF voltage suppliers provided according to embodiments of the present invention.

Abstract: An unstable optical resonator device is provided, comprising a spherical back mirror, a spherical outcoupling mirror, wherein a focal point lies between the back mirror and the outcoupling mirror, an optically active medium with a rectangular medium cross-section arranged between the back mirror and the outcoupling mirror, and a scraper, which is arranged between the back mirror and the outcoupling mirror and has a first leg and a second leg located transversely to the first leg, said legs defining a free space with a first side delimited by the first leg and a second side delimited by the second leg, wherein the first side and the second side are orthogonal to one another.

Abstract: A deep ultraviolet light source includes a master oscillator producing a seed light beam; a regenerative ring amplifier receiving the seed light beam from the master oscillator and outputting an output light beam, the regenerative ring amplifier including a set of optical components that define a plane of a closed ring; and a divergence control device within the master oscillator or between the master oscillator and the regenerative ring amplifier and configured to reduce a divergence of the output light beam along a normal direction, the normal direction being perpendicular to the plane of the ring.

Abstract: A laser amplifier system is provided which comprises a resonator with optical resonator elements which determine a course of a resonator radiation field which propagates along an optical axis and at least one laser-active medium (LM). The resonator is designed as a split resonator and has a first resonator section which extends from a first virtual plane of separation and a second resonator section which extends from a second virtual plane of separation. The resonator sections are dimensioned optically such that the resonator radiation field has radiation field states corresponding to the same resonator modes in each of the virtual planes of separation. An amplifying unit optically independent of the resonator is arranged between the first and the second virtual planes of separation. The amplifying unit comprises the at least one laser-active medium and couples the radiation field states in a neutral manner with respect to the resonator modes.

Abstract: A monoblock laser cavity incorporates optical components for a short-pulse laser. These optical components are ‘locked’ into alignment forming an optical laser cavity for flash lamp or diode laser pumping. The optical laser cavity does not need optical alignment after it is fabricated, increasing the brightness of the monoblock laser.

Abstract: A method of using a discriminant analysis and Kalman filter cascade to improve the accuracy of point of origin solutions. Tracking information about a potential target is utilized by an initial discrimination function to classify the target as a projectile. Using that information, the output of a first Kalman filter is fed into an additional discrimination function to further classify the type or sub-class of the projectile. A second Kalman filter can employ type-specific information to obtain a point of origin solution with increased efficiency and accuracy.

Abstract: A laser amplifier system is provided which comprises a resonator with optical resonator elements which determine a course of a resonator radiation field which propagates along an optical axis and at least one laser-active medium (LM). The resonator is designed as a split resonator and has a first resonator section which extends from a first virtual plane of separation and a second resonator section which extends from a second virtual plane of separation. The resonator sections are dimensioned optically such that the resonator radiation field has radiation field states corresponding to the same resonator modes in each of the virtual planes of separation. An amplifying unit optically independent of the resonator is arranged between the first and the second virtual planes of separation. The amplifying unit comprises the at least one laser-active medium and couples the radiation field states in a neutral manner with respect to the resonator modes.

Abstract: A laser system including two laser amplifier modules, each comprising a solid-state laser gain material (LGM) disk, and a multi-pass optical assembly comprising a plurality of relay mirrors. The relay mirrors are grouped in two relay mirror groups. Individual relay mirrors are arranged to pass a laser beam from the first LGM disk to the second LGM disk and back to the first LGM disk, and so on. The laser beam is amplified with each pass through the LGM disk. The relay mirrors may be arranged to repeat the process of passing the laser beam to and from the two LGM disks arbitrary number of times until the desired laser beam amplification is attained. At that point, the laser beam may either released from the laser system, reflected back causing it to retrace its path through the system. This configuration increases the effective gain and improves laser power extraction.

Abstract: A light emitting device includes a substrate, a first cladding layer, an active layer, and a second cladding layer formed in that order, and a reflective part formed above the substrate and separated from the active layer. At least a portion of the active layer constitutes a plurality of gain regions, which forms at least one gain region pair, a first gain region of which is provided in one direction and a second gain region is provided in another direction different from the one direction. At least a portion of an end surface of the first gain region and the second gain region overlap with each other. Light emitted from the end surface of the first gain region is reflected by the reflective part, and propagates in the same direction or in the focusing direction with light emitted from the end surface of the second gain region.

Abstract: A gas laser device is presented that produces a near diffraction limited round beam exiting the discharge vessel. Through the use of a simple focusing system, additional waveguide strip and a spatial filter in conjunction with the new asymmetric hybrid planar waveguide resonator, a round diffraction limited beam can be produced exiting the discharge vessel. Furthermore, a second and very similar design is presented that allows for spatial filtering to take place directly outside of the discharge vessel, thereby enabling filtering of the beam to be an added option.

Abstract: A laser includes a regenerative ring resonator that includes a discharge chamber having electrodes and a gain medium between the electrodes for producing a laser beam; a partially-reflective optical coupler, and a beam modification optical system in the path of the laser beam. The beam modification optical system transversely expands a profile of the laser beam such that the near field laser beam profile uniformly fills each aperture within the laser and such that the regenerative ring resonator remains either conditionally stable or marginally unstable when operating the laser at powers that induce thermal lenses in optical elements inside the regenerative ring resonator.

Abstract: A mode selection technique in a laser is described wherein a recess is formed in a surface of a waveguide in the laser. The recess provides a region of free space propagation within the waveguide which preferentially selects the lowest order mode. A mode selective RF excited CO2 slab laser, having a stable resonator in the waveguide dimension and a negative branch unstable resonator in the non-waveguide dimension, is constructed and the position and size of the recess is considered to provide low order mode selection.

Abstract: An unstable laser disk resonator combines the output laser power of multiple laser disks to produce a high power, single transverse mode laser output beam, which is near diffraction limited.

Abstract: An unstable optical resonator device is provided, comprising a spherical back mirror, a spherical outcoupling mirror, wherein a focal point lies between the back mirror and the outcoupling mirror, an optically active medium with a rectangular medium cross-section arranged between the back mirror and the outcoupling mirror, and a scraper, which is arranged between the back mirror and the outcoupling mirror and has a first leg and a second leg located transversely to the first leg, said legs defining a free space with a first side delimited by the first leg and a second side delimited by the second leg, wherein the first side and the second side are orthogonal to one another.

Abstract: A laser includes a regenerative ring resonator that includes a discharge chamber having electrodes and a gain medium between the electrodes for producing a laser beam; a partially-reflective optical coupler, and a beam modification optical system in the path of the laser beam. The beam modification optical system transversely expands a profile of the laser beam such that the near field laser beam profile uniformly fills each aperture within the laser and such that the regenerative ring resonator remains either conditionally stable or marginally unstable when operating the laser at powers that induce thermal lenses in optical elements inside the regenerative ring resonator.

Abstract: A coherent beam source, e.g., a laser having a cavity that is unstable in at least one direction, is used to produce a coherent beam having an initial intensity profile. The beam is passed through a relay having a Fourier plane containing a spatial filter that serves as a radiation defining mask. The filter has an aperture size and shape effective to modify the beam such that the modified beam forms an image on a substrate. The to image has an intensity profile that more closely approximates a super-Gaussian profile than the initial profile. For example, when the initial intensity profile is Gaussian, the spatial filter may allow passage of only unattenuated the central core of the beam and block completely blocks the wings of the Guassian profile. The modified beam may be more suitable for use in a scanning system used to anneal wafers or other substrates containing integrated circuits.

Abstract: Helper resonators useful for the reliable, controlled startup of an associated high power multidisk unstable imaging thin disk laser (TDL) main resonator each includes one of the thin disk gain elements (TDGEs) of the associated main resonator and a pair of helper reflectors disposed on opposite sides thereof. The helper resonators act to prevent the buildup of undesirable amplified spontaneous emission (ASE) during startup of the main resonator, pre-condition the TDGEs so as to enable efficient power transfer from the helper resonators to the main resonator when the main resonator reaches a selected feedback ratio (FBR) and provide a rapidly acting shunt for disk power in the event of a cessation of lasing of the main resonator.

Abstract: An unstable optical resonator for an optically active medium comprising a spherical back mirror and a spherical outcoupling mirror is proposed, and an outcoupling which is asymmetrical in relation to the optical axis takes place therein.

Abstract: Through the use of a relatively inexpensive third mirror on a novel folded hybrid unstable resonator configuration, the optimum output coupling for a given laser design can be explored quickly and easily with a minimum of intracavity mirror alignment. No changes in either the radii of curvature of the three cavity optics or their spacing are required for this exploration. In addition to providing techniques for purposefully and systematically introducing mirror edge effects or avoiding edges effects altogether, the invention provides that output beams of different width can be advantageously explored in a relatively simple and straightforward manner. The invention provides that higher geometric magnification cavity designs may be made compatible with low diffraction output coupling in a configuration that uses only three totally reflecting optics.

Abstract: An improved resonator and optical cavity is adapted for use with a chemical laser that has a nozzle upstream of the resonator that emits a gain medium in a flow direction, and a pressure-recovery system downstream of the resonator. The optical resonator comprises first and second optical elements that are spaced apart from one another along an optical axis. Each of the optical elements has a selected geometry and a selected optical transmissivity to permit transmissive outcoupling of a beam of laser radiation from the resonator, the outcoupled beam being transmitted about the optical axis. The transmissivity and geometry of each optical element is selected to define an unstable region between the optical elements and around the optical axis, and a stable region in a region surrounding the unstable region and spaced apart from the optical axis.

Abstract: A configuration for an unstable, negative branch imaging resonator (NBIR) is disclosed in which coupling mirrors are added so that the Primary and Secondary mirrors are not in direct optical communication with the imaging systems which minimizes the occurrence of the NBIR experiencing magnification runaway and/or odd order aberrations by using coupling mirrors to provide indirect optical communication between the imaging systems and the Primary and Secondary end mirrors.

Abstract: External-cavity optically-pumped semiconductor lasers (OPS-lasers) including an OPS-structure having a mirror-structure surmounted by a surface-emitting, semiconductor multilayer (periodic) gain-structure are disclosed. The gain-structure is pumped by light from diode-lasers. The OPS-lasers can provide fundamental laser output-power of about two Watts (2.0 W) or greater. Intracavity frequency-converted arrangements of the OPS-lasers can provide harmonic laser output-power of about one-hundred milliwatts (100 mW) or greater, even at wavelengths in the ultraviolet region of the electromagnetic spectrum. These high output powers can be provided even in single axial-mode operation.

Abstract: An unstable laser disk resonator combines the output laser power of multiple laser disks to produce a high power, single transverse mode laser output beam, which is near diffraction limited.

Abstract: An optical resonator has an internal cavity with an output coupler, an end mirror, and one or more active mirror amplifiers (AMAs) that are arranged in a manner to form a laser radiation propagation path within the cavity which substantially has the form of a star polygon trajectory.

Abstract: A high-powered mid-IR antimonide-based unstable resonator semiconductor laser that is optically pumped. One Fabry-Perot facet is a mechanically polished cylindrical mirror that extends well into the GaSb substrate. The waveguide is designed to weakly confine the transverse optical mode, and the optical pump stripe width can be varied to optimize the cavity width for high brightness operation.

Abstract: A unidirectional ring laser oscillator has a travelling wave unstable mode in one transverse dimension and either a waveguide or freespace Gaussian mode in the orthogonal transverse dimension for coupling to large volumes of asymmetric cross section laser gain media. This device concept is shown to have unique and innovative features such as an exchange of left for right in the intracavity radiation profile without having to employ concave optics. Also, a high insensitivity to misalignment of one of the intracavity ring optics is achieved without having to suffer any deleterious effects associated with the high intensity of radiation normally encountered at an intracavity focal plane. Unidirectional operation of the laser is achieved using both intracavity and extracavity optical techniques.

Abstract: An unstable optical resonator for an optically active medium comprising a spherical back mirror and a spherical outcoupling mirror is proposed, and an outcoupling which is asymmetrical in relation to the optical axis takes place therein.

Abstract: A variable light controlling device comprising a substrate, an optical waveguide disposed on the substrate, a first heater and a second heater to change the optical waveguide's temperature is fabricated. And a total amount of the power supplied to the first and the second heater, or a total amount of heat emitted from both of the first and second heater, is maintained substantially constant. Then, the substrate is protected from temperature changes, thereby, stable and quick wavelength tuning operations are realized.

Abstract: Through the use of a relatively inexpensive third mirror on a novel folded hybrid unstable resonator configuration, the optimum output coupling for a given laser design can be explored quickly and easily with a minimum of intracavity mirror alignment. No changes in either the radii of curvature of the three cavity optics or their spacing are required for this exploration. In addition to providing techniques for purposefully and systematically introducing mirror edge effects or avoiding edges effects altogether, the invention provides that output beams of different width can be advantageously explored in a relatively simple and straightforward manner. The invention provides that higher geometric magnification cavity designs may be made compatible with low diffraction output coupling in a configuration that uses only three totally reflecting optics.

Abstract: An unstable optical resonator for an optically active medium comprising a spherical back mirror and a spherical outcoupling mirror is proposed, and an outcoupling which is asymmetrical in relation to the optical axis takes place therein.

Abstract: The invention provides a cascaded injection resonator for coherent beam combining of laser arrays. The resonator comprises a plurality of laser emitters arranged along at least one plane and a beam sampler for reflecting at least a portion of each laser beam that impinges on the beam sampler, the portion of each laser beam from one of the laser emitters being reflected back to another one of the laser emitters to cause a beam to be generated from the other one of the laser emitters to the beam reflector. The beam sampler also transmits a portion of each laser beam to produce a laser output beam such that a plurality of laser output beams of the same frequency are produced. An injection laser beam is directed to a first laser emitter to begin a process of generating and reflecting a laser beam from one laser emitter to another laser emitter in the plurality. A method of practicing the invention is also disclosed.

Abstract: The invention relates to a short-pulse laser device (11) with a preferably passive mode coupling. Said device comprises a resonator (12) which contains a laser crystal (14) in addition to several mirrors (M1-M7, OC) that define a long resonator arm (17) and a short resonator arm (16), one (M1) of said mirrors forming a pump beam coupling-in mirror and another (OC) forming a laser beam output coupler and comprising a multiple reflection telescope (18) that increases the length of the resonator and is allocated to the resonator arms (16, 17). Said telescope is constructed using mirrors (25, 26), in order to reflect a laser beam (15) that is coupled into the space between them back and forth several times, prior to being decoupled back into the other resonator, whereby sequential eccentric reflection points (1 to 8; 1? to 8?) on the mirrors (25, 26) are offset in relation to one another.

Abstract: An improved resonator and optical cavity is adapted for use with a chemical laser that has a nozzle upstream of the resonator that emits a gain medium in a flow direction, and a pressure-recovery system downstream of the resonator. The optical resonator comprises first and second optical elements that are spaced apart from one another along an optical axis. Each of the optical elements has a selected geometry and a selected optical transmissivity to permit transmissive outcoupling of a beam of laser radiation from the resonator, the outcoupled beam being transmitted about the optical axis. The transmissivity and geometry of each optical element is selected to define an unstable region between the optical elements and around the optical axis, and a stable region in a region surrounding the unstable region and spaced apart from the optical axis.

Abstract: An apparatus and method for achieving a near diffraction-limited, high-average power output from a solid-state laser oscillator are provided. The solid-state laser uses multiple disk-shaped laser gain media having a large optical aperture placed in an unstable resonator. The laser gain media is provided with optical coatings for operation in the active mirror configuration and is attached to a rigid, cooled substrate, which allows it to maintain a prescribed shape even when experiencing significant thermal load. The resonator is configured so as to preferentially support low order optical modes with transverse dimensions sufficiently large to efficiently fill the gain media apertures. Resonator configurations capable of producing standing wave or traveling wave optical fields are disclosed. The resonator may include means for intracavity correction of an optical phase front by adaptive optics.

Abstract: A compact optical resonator that exhibits long TOPLs is fabricated by (a) selecting a 3-dimensional (3D) reflective, essentially closed surface such that the paths of optical rays that reflect from the interior of the surface include chaotic, open paths; (b) determining the phase-space of the reflection points of the rays; (c) within the phase-space identifying at least one forbidden zone where there are no such reflection points and at least one allowed zone where there is a multiplicity of such reflection points; (d) forming the surface inside a rigid body; and (e) forming at least one physical feature that communicates with the interior of the resonator and is located in a region of the surface that is determined by the positions of the forbidden zones, the allowed zones, or both. In a preferred embodiment physical features such as gas ports are located in regions of the surface that, in phase space, correspond to forbidden zones (so that the circulating optical rays cannot escape via the gas ports).

Abstract: A semiconductor laser module in which an exciting laser beam output is always allowed to be in a multi-mode and the variation of optical output does not occur. In the semiconductor laser module, a semiconductor laser device, light coupling means and an optical fiber are disposed, and further, a light feedback (return) portion where a laser beam of a specific wavelength is reflected is formed, and the reflection spectrum at the light feedback portion has a shape similar to a rectangular one.

Abstract: The laser resonator system includes a first reflector; a second reflector; at least a first gain medium; a second gain medium; and, an Offner relay system. The first gain medium and the second gain medium are operatively positioned relative to the first and the second reflectors. The first and second gain media generate a laser beam. The Offner relay system is operatively positioned between the first and the second gain media for relaying the laser beam between the first and the second gain media. The laser resonator system uses the Offner relay system for optimal transmission of the laser beam between the two gain media.

Abstract: An optical amplifier arrangement, including an amplifying medium, which exhibits an approximately rectangular cross section with a long edge and a short edge, as well as at least two highly reflecting mirrors, between which the amplifying medium is disposed, whereby the long or the short edge of the cross section is along the X axis or the Y axis; the Z axis is the optical axis; and the X, Y and Z axis form a rectangular coordinate system. The mirrors are designed and arranged in such a manner that one beam, which is to be amplified and beamed in by an oscillator, passes repeatedly through the amplifying medium in the XZ plane and is amplified; and the size of the beam to be amplified in the X direction becomes larger after each passage.

Abstract: An actuator for continuously aligning the primary mirror relative to the scraper the other resonator mirrors and the feedback mirror in a high power laser resonator, comprised of extended portions of the resonators primary mirror, feedback mirror and scraper mirror for a low power laser beam to travel parallel to but offset from the high power laser beam for aligning the mirrors. The low power laser beam is used to measure the position of the mirrors in the resonator. The low power beam is split into a beam which is incident on a quadrant cell for measuring the tip and tilt of the feedback mirror relative to the primary mirror and a beam which measures the translation of the feedback mirror relative to the primary mirror. A controller receives the data form the quadrant cells and sends signals to actuators on one mirror to move it relative to the other thus keeping the mirrors in constant alignment.

Abstract: A CO2 laser utilizing combination of direct current (DC), radio frequency (RF) discharges together with an unstable resonator is disclosed. The combined use of the combination of DC and RF discharges in the laser apparatus allows to provide high power output radiation within a relatively compact design of the apparatus. Consequently, the laser operating efficiency is increased, with a significant lowering of required excitation voltages, and a substantial reduction in excitation hardware. The laser apparatus of the present invention may have durable and reliable construction that is relatively easy and cheap in manufacturing.

Abstract: An apparatus and method for achieving a near diffraction-limited, high-average power output from a solid-state laser oscillator are provided. The solid-state laser uses multiple disk-shaped laser gain media having a large optical aperture placed in an unstable resonator. The laser gain media is provided with optical coatings for operation in the active mirror configuration and is attached to a rigid, cooled substrate, which allows it to maintain a prescribed shape even when experiencing significant thermal load. The resonator is configured so as to preferentially support low order optical modes with transverse dimensions sufficiently large to efficiently fill the gain media apertures. Resonator configurations capable of producing standing wave or traveling wave optical fields are disclosed. The resonator may include means for intracavity correction of an optical phase front by adaptive optics.

Abstract: An apparatus and method for achieving a near diffraction-limited, high-average power output from a solid-state laser oscillator are provided. The solid-state laser uses multiple disk-shaped laser gain media having a large optical aperture placed in an unstable resonator. The laser gain media is provided with optical coatings for operation in the active mirror configuration and is attached to a rigid, cooled substrate, which allows it to maintain a prescribed shape even when experiencing significant thermal load. The resonator is configured so as to preferentially support low order optical modes with transverse dimensions sufficiently large to efficiently fill the gain media apertures. Resonator configurations capable of producing standing wave or traveling wave optical fields are disclosed. The resonator may include means for intracavity correction of an optical phase front by adaptive optics.

Abstract: A stable multi-fold telescopic resonator is applied to a slab laser to provide a high power laser beam of a high optical quality. The current invention could be applied to both waveguide and free-space slab lasers with either gas or solid-state active media. A reduced sensitivity to misalignment is achieved through the use of two short-radii concave folding mirrors forming a nearly-confocal or confocal optical resonator. In order to obtain a nearly-symmetrical output beam profile from the large thickness slab lasing medium, the resonator includes a slit diaphragm(s), positioned between the slab and resonator mirrors and aimed to eliminate higher order laser modes in the direction transverse to the plane of the slab. Furthermore, a three mirror multi-fold telescopic resonator is provided by substituting one of the resonator mirrors with a surface of one of the folding mirrors.

Abstract: An unstable optical cavity for laser beams, having at least 3 deflection means for making a beam created in the cavity undergo at least three changes in direction so to form an optical ring path, and an optical magnification set disposed among the deflecting means. The at least 3 deflection means are prisms, each of which has an air-glass reflecting interface that provides one of the changes in direction by total reflection. A first of the at least 3 prims is positioned at an output of the cavity and has an air-glass reflecting interface with an insufficient size for a total reflection of the beam in the cavity, and remaining ones of the prisms have an air-glass reflecting interface with a sufficient size for a total reflection of the beam in the cavity.