Abstract: A solid-state tunable laser having a ND:YAG pumping source, a chromium-doped fosterite crystal lasing medium, a birefringent filter for selecting a specific fundamental wavelength, a pair of harmonic generating crystals mounted on counter-rotating platforms driven by stepper motors under the control of a computer, a partially reflective, partially transmissive mirror for directing the output of the pumping source through the lasing medium so that the lasing medium produces radiation having a range of fundamental wavelengths, and a fully reflective mirror for directing the radiation of the specific fundamental wavelength through the birefringent filter and the pair of crystals so as to produce radiation of a harmonic wavelength of the specific fundamental wavelength.

Abstract: A laser beam generating apparatus which is easy to manufacture and simple in adjusting operation. The laser beam generating apparatus comprises a light source having a narrow active layer for generating pumping laser beam, a laser medium for receiving the pumping laser beam to form a heat lens therein and generate a fundamental wave laser beam, a non-linear optical crystal element having a face inclined with respect to an optical axis of the fundamental wave laser beam for receiving the fundamental wave laser beam to generate secondary harmonic laser beam, a quarter wavelength plate for suppressing coupling between two polarization modes of the fundamental wave laser beam, and a pair of planar reflecting means for reflecting the fundamental wave laser beam back into the laser medium. The laser medium, non-linear optical crystal element, quarter length plate and planar reflecting means cooperate to constitute a light resonator.

Abstract: In an optical wavelength converting apparatus, a laser beam serving as a fundamental wave and having been obtained by pumping a solid laser medium is caused to impinge upon a nonlinear optical crystal, and the type II of phase matching between the fundamental wave and its second harmonic is effected. The second harmonic of the fundamental wave is thereby radiated out of the optical wavelength converting apparatus. A solid laser medium, which produces a linearly polarized fundamental wave in two longitudinal modes, is employed as the solid laser medium. A device for adjusting a difference in phase of the fundamental wave due to the nonlinear optical crystal and a device for adjusting the temperatures of the nonlinear optical crystal and a resonator, such that the temperatures may be kept at predetermined values, are provided in order to work such that two directions of polarization of the fundamental wave may intersect approximately perpendicularly to each other and may respectively incline approximately 45.

Abstract: A mode locked pulsed laser incorporates an intracavity element to compensate for the dispersion caused by other intracavity elements. This element reduces the tendency of the pulse to broaden in the cavity due to group velocity dispersion and results in very short pulses. In the laser of the present invention, mode locking is initiated by detecting the beat frequency between adjacent longitudinal modes using a high speed photodiode. This signal is amplified and then the frequency is divided by two. The signal is passed through an electronically adjustable phase shifter and then to a power amplifier. This signal is applied to the acousto-optic modelocker. If the cavity length drifts the beat frequency between the longitudinal modes changes. The rf signal applied to the modulator changes in exactly the right manner to track the drift in cavity length. Thus the modelocker is automatically synched to the round trip of the laser cavity.

Abstract: In a random polarization gas laser tube, a pair of mirrors constituting an optical resonator have anisotropic characteristics and aligned such that directions showing highest reflection intensity are orthogonal to each other to obtain a stable polarizing characteristics.

Abstract: A flashpumped, tunable, two-micron, solid state laser is disclosed in which laser spiking is suppressed. The solid state laser comprises: a laser cavity defined by a first reflective element and an output coupler reflective element to form a reflective path therebetween; a laser crystal disposed in the laser cavity, the laser crystal having a host material doped with preselected activator ions sufficient to produce a pulse of laser emission at a desired laser transition wavelength in a range between about 1.9 microns and about 2.1 microns when the crystal is optically excited to produce the laser emission; a pulsed flashlamp for optically exciting the laser crystal to produce a pulse of laser emission at the desired laser transition wavelength; a tuner disposed in the laser cavity between the laser crystal and one of the reflective elements for tuning the laser emission to the desired laser transition wavelength in the range of wavelengths between about 1.9 microns and about 2.

Abstract: An unstable laser with improved beam quality has a laser medium and a pair of crossed Porro prism end reflectors positioned to form a resonator defining a light path through the laser medium. Beam expansion optics magnify the beam with each pass through the resonator and is accomplished with a negative lens at one end of the resonator and a telescope at the other end. The negative lens produces a diverging beam through a laser medium in one direction and the telescope recollimates the beam in the reverse direction. Radially varying birefringent compensation is accomplished in the resonator with a crystalline waveplate. Output coupling is achieved through the use of the waveplate in conjunction with polarizer optics.

Abstract: A solid state laser apparatus in which a fundamental laser beam generated in a laser medium is resonated so as to pass a nonlinear optical crystal element provided within a resonator to thereby generate a secondary harmonic laser light and a first optical element for suppressing a coupling caused by a sum-frequency generation between two polarization modes of the fundamental wave laser beam is provided within the resonator includes of a control device for controlling an effective resonator length of the resonator such that the two polarization modes of the fundamental wave laser beam become the same in oscillation intensity. Therefore, a mode hopping noise caused by the mode coupling of the fundamental laser beam within the same polarization mode can be avoided and the oscillation can be stabilized.

Abstract: A frequency doubled ultraviolet laser comprising means for enabling a beam of coherent electromagnetic radiation to be propagated along an intracavity path, means for holding and translating an anisotropic crystal in this path, means for detecting the crystal temperature relative to the optimum frequency doubling temperature, and means for correcting any shortfalls in the efficiency of ultraviolet generation by adjusting the crystal temperature, crystal position, and/or the intensity of the fundamental beam.

Abstract: The present invention provides a means of inducing unidirectional oscillation in monolithic and composite ring lasers in which the light path is planar. The intracavity optical diode that enforces unidirectional oscillation in the planar ring oscillator is achieved by a combination of the nonreciprocal Faraday effect, a linear birefringence effect in which the principal axes of the birefringence are not parallel and perpendicular to the plane of propagation of the ring light path, and one or more partial polarizer effects. The present invention enables experimental optimization of polarization transformations within a planar ring oscillator, even if the oscillator is monolithic, and also provides a means of tuning the frequency of the planar ring oscillator.

Abstract: Disclosed is a laser apparatus having an optical pumping source, first and second resonator mirrors, a laser medium provided on a light route between the first and second resonator mirrors, an optical system provided in a light route between the laser medium and the second resonator mirror; and a nonlinear optical crystal for generating through wavelength conversion a higher harmonic wave(s) from a fundamental wave of laser generated by the laser medium. The nonlinear optical crystal is capable of being inserted between the intermediate optical system and the second resonator mirror. The second resonator mirror is a concave mirror. The intermediate optical system is constituted by a single concave mirror reflecting the fundamental wave and transmitting the higher harmonic wave(s).

Abstract: An improved dye laser having a birefringent tuning filter comprised of one or more birefringent plates wherein each plate is oriented at Brewster's angle to the resonant light beam and is an integer multiple of the thickness of the thickness of the first plate characterized by the fact that the thickness of the first plate is chosen using a new tuning relationship so that a single order tuning curve covers a tuning range of interest. This single tuning curve is almost linear throughout the tuning range and has a tuning angle at the center of the range of approximately five degrees. Also, the tuning curve has a slope throughout the tuning range which provides sensitivity of selected wavelength to tuning angle which is neither too great nor too small. A further refinement in the structure is a non-birefringent polarizing plate at Brewster's angle which increases the losses imposed upon light passing therethrough which is polarized at other than Brewster's angle.

Abstract: A system for controlling the polarization of lasers is described in which the polarization of laser radiation generated in a gain cavity is controlled by feedback of a controlled amount of polarized light from a polarizing cavity. The output mirror of the gain cavity forms an input mirror of the polarizing cavity.

Abstract: A birefringent filter ("BRF") unit, for use in the cavity of a tunable pulsed laser generating ultrashort pulses, including means for suppressing satellite pulses resulting from surface reflections. In one preferred embodiment, the inventive BRF has substantially parallel front and back surfaces, and is cut so that its optical axis is not parallel to its front surface. For example, the inventive BRF may be a quartz crystal having a thickness of 3 mm, with its optical axis oriented at an angle substantially equal to 50 degrees from the plane of its front surface. In a second preferred embodiment, the inventive BRF includes a relatively thick, non-birefringent component coupled with index matching material to a relatively thin birefringent component. In a third preferred embodiment, the inventive BRF includes a pair of thick birefringent components designed so that the ordinary ray of the first component becomes the extraordinary ray of the second component.

Abstract: Rotational displacement of the birefringent lasing medium in a lasing cavity containing a polarizing element varies the spectral width of the generated laser light. The combination in a lasing cavity of a birefringent lasing medium, a polarizing element, a tuning element and a birefringent compensator permits output of narrow bandwidth spectrally tuned laser light continuously over the total gain bandwidth of the lasing medium by rotating the lasing medium, tuning to desired wavelength, and adjusting the birefringent compensator to optimize output of laser light.

Abstract: An improved geometry is disclosed for enhancing the efficiency of second harmonic conversion in a Type II phasematching material. In this approach, the effects of wave vector double refraction are used to compensate for the effects of Poynting vector walk-off. To achieve this goal, the input fundamental beam 32 is arranged to enter the doubling crystal 30 at an oblique angle of incidence. This angle is selected so that the wave vector double refraction angle is equal to the Poynting vector walk-off. In order to maximize doubling efficiency, the axes of the crystal must be oriented so that the optimum phasematching angle coincides with the propagation axis of the refracted fundamental beam travelling in the crystal. The subject invention is particularly suited for use with a KTP crystal in either intracavity doubling or in an external resonant geometry.

Abstract: A laser amplifier in which the effective refractive index of the active region for the TE and TM modes is sufficiently different to provide multiple mode ripple beat frequency overlap within a 3dB gain envelope peak. The active region is made highly asymmetric with an aspect ratio of at least 10:1 and preferably 20:1 in order to provide the effective refractive index difference. Steps, grading or uniform difference in the material refractive index may also be used. The confinement factor ratio is made as high as possible by providing different material refractive index in the orthogonal dimensions of the active region cross section.

Abstract: A laser system generates suitable laser power for use in photodynamic therapy, and particularly photodynamic therapy using dyes which undergo desired photodynamic reactions at 659 mm, i.e., Purpurin. The laser system generates a red output power of greater than 4 watts. For the therapeutic applications, a means for delivering the red beam to therapeutic sites is provided. The laser system provides for a frequency doubled solid-state laser system in which the non-linear birefringent crystal used to provide frequency doubling is mounted adjacent a flat mirror whereby losses due to walkoff of the beam caused by the crystal are minimized. The laser resonant cavity defined by one flat and one other mirror, which may be stabilized by means, such as thermal lensing in the solid-state gain medium, inside the cavity. A frequency doubled Nd:YAG rod in such cavity tuned to 1.319 microns with a KTP frequency doubling crystal for generates an output beam at 0.

Abstract: Device able to continuously tune a coherent and rectilinearly polarized light source. It includes an electro-optical device (5) forming a spectral filter with an electrically modulable transfer function, this electro-optical device being provided so as to select a particular longitudinal mode from all the longitudinal modes able to oscillate inside the external cavity for which the source (1) is provided and which is ended by a reflecting device (3) towards the source of the light emitted by this source, and an electro-optical device (4) for varying the optical length of the cavity, this variation device being placed in the cavity and provided so as to continuously move the position of the selected longitudinal mode, each electro-optical device including a compact electro-optical crystal.

Abstract: Solid state and dye lasers are described which are tunable over a wide spectral region, are operable at high repetition rate, are uniformly narrow in spectral width over the tuning range, and produce a spatially uniform, single longitudinal mode beam. In one embodiment having a simple grazing-incidence cavity, the laser comprises: (a) a longitudinal pump beam with a KiloHertz (KHz) repetition rate; (b) a resonating cavity comprising a first fixed mirror, a diffraction grating, and a second rotatable mirror; and (c) an active solid state or dye medium within the cavity. In this embodiment, (i) the pump beam is passed through the fixed mirror and directed at the active medium; (ii) the emission from the active medium strikes the grating near a grazing angle; (iii) the rotatable mirror is placed at a first order diffraction position from the grating and reflects the desired wavelength radiation back into the cavity; and (iv) the output is derived from the grating at the zeroeth diffraction order.

Abstract: An antiresonant nonlinear mirror to replace one mirror of a laser for passive modelocking of the laser, the antiresonant nonlinear mirror comprising: a beam splitter for coupling the mirror to a laser cavity; a mirror arrangement for defining an optical ring with the beam splitter in which two light beams produced by the beam splitter in response to a light beam from the laser cavity can counterpropagate around the ring; an intensity dependent anisotropic nonlinear element disposed within the ring; and a polarization sensitive element disposed within the ring for adjusting the birefringence thereof to produce spontaneous modelocking in the coupled laser cavity.

Abstract: To supply a frequency control signal to a laser diode module for generating a laser beam susceptible to a variation in frequency or wavelength, a frequency stabilizing device comprises a birefringent body (21) for converting the variation to a variation in a polarization state of the laser beam to produce a polarization varied beam, which a polarization separating element (22) separates into first and second beam components having orthogonally polarized directions and first and second beam intensities. Optical detectors (26,27) detect the beam intensities to produce first and second detection signals. A subtracter (28) calculates a difference between the beam intensities. A control signal producing arangement (29) produces the frequency control signal in compliance with the difference. Preferably, the difference is normalized by a sum of the beam intensities. The birefringent body may be a uniaxial or a biaxial body. The uniaxial body should have an optic axis which forms an angle of 45.degree.

Abstract: A tunable solid state laser for producing a laser emission at any desired w or high laser gain transition in a predetermined range of wavelengths is disclosed. The tunable solid state laser comprises: a laser cavity defined by a first reflective element and an output coupler reflective element to form a reflective path therebetween; a laser crystal disposed in the laser cavity; means for optically exciting the laser crystal to produce a laser emission in the predetermined range of wavelengths; a tunable element disposed in the laser cavity between the laser crystal and one of the reflective elements for tuning the laser emission to any desired laser transition in the predetermined range of wavelengths; and a plurality of optical plates oriented at Brewster's angle in the reflective path in the laser cavity for suppressing oscillation of undesired wavelengths within the laser cavity, the optical plates being transparent to the laser emission over the predetermined range of wavelengths.

Abstract: In a gas laser having integrated mirrors wherein two longitudinal modes of the laser oscillation are excited during operation, and wherein the oscillatory planes thereof reside perpendicularly relative to one another, a stabilization of the angular position of the oscillatory planes is achieved in that an optically birefringent element is arranged in the beam path of the optical resonator.

Abstract: A birefringent quartz plate is inserted in the laser cavity to generate two orthogonal polarized beams with different frequencies, and with the amount of frequency difference depending upon the angle of orientation of the crystalline axis of the quartz plate with respect to the longitudinal axis of the laser beam in the cavity. Frequency differences between the generated dual frequency beams can be varied from tens of MHz to more than 1000 MHz, with tuning or variation being effected by a mechanism for rotating the quartz plate. This apparatus provides a dual-frequency laser for interferometry, laser Doppler velocimeters and other applications.

Abstract: A laser for use in all fields of measurement using a heterodyne effect delivers two waves at different frequencies, having mutually orthogonal linear polarizations. It comprises a lasing medium placed in a laser resonating cavity defined by mirrors and a birefringent crystal placed on the path of the two waves. The lasing medium is located in the resonating cavity in a zone where the two waves are separated spatially. Two quarter wave plates, one of which has neutral lines at substantially 45.degree. from the polarization axes of the birefringent means, are placed in the common path of the two waves so as to give a helical polarization to the two waves between the plates.

Abstract: A birefringent filter is provided for tuning the wavelength of a broad band emission laser. The filter comprises thin plates of a birefringent material having thicknesses which are non-unity, integral multiples of the difference between the thicknesses of the two thinnest plates. The resulting wavelength selectivity is substantially equivalent to the wavelength selectivity of a conventional filter which has a thinnest plate having a thickness equal to this thickness difference. The present invention obtains an acceptable tuning of the wavelength while avoiding a decrease in optical quality associated with conventional filters wherein the respective plate thicknesses are integral multiples of the thinnest plate.

Abstract: Alignment of a birefringent device characterized by a first face and a second face cut at Brewster's angle so that a plane of polarization is defined. The optical device is secured in the optical path by a rotatable member having an axis of rotation that is normal to the Brewster faces of the optical device. Coupled with the rotatable member on the axis of rotation is a support allowing adjustment of the angular position about the axis of rotation of the rotatable member. An operator adjusts the angular position of the rotatable member until the C-axis lies in the plane of polarization. Even though the C-axis may not be parallel to the direction of polarization, the depolarization effects of the misalignment are eliminated by proper adjustment of the angular position relative to the plane of polarization. A tunable, solid state laser using the alignment apparatus with a birefringent filter achieves greater linear tuning range.

Abstract: A laser system employing one or more mirror sets having substantially astigmatism-free focusing power sufficient to maintain a desired laser beam diameter, for example, to compensate for thermally-induced distributed lensing. In one class of preferred embodiments, the invention is a high power gas laser system having a folded optical cavity with a periodic intracavity refocusing means to compensate for distributed negative thermal lensing in the hot plasma that comprises the active medium, and thus maintain a substantially constant beam diameter throughout the optical cavity. The periodic intracavity refocusing means preferably includes a corner mirror set (including at least one curved mirror and at least one other mirror) at each corner of the folded optical cavity. In one preferred embodiment, each corner mirror set is a mirror pair including a spherical mirror and cylindrical mirror.

Abstract: A birefringent filter ("BRF") unit, for use in the cavity of a tunable pulsed laser generating ultrashort pulses, including means for suppressing satellite pulses resulting from surface reflections. In one preferred embodiment, the inventive BRF has substantially parallel front and back surfaces, and is cut so that its optical axis is not parallel to its front surface. For example, the inventive BRF may be a quartz crystal having a thickness of 3 mm, with its optical axis oriented at an angle substantially equal to 50 degrees from the plane of its front surface. In a second preferred embodiment, the inventive BRF includes a relatively thick, non-birefringent component coupled with index matching material to a relatively thin birefringent component. In a third preferred embodiment, the inventive BRF includes a pair of thick birefringent components designed so that the ordinary ray of the first component becomes the extraordinary ray of the second component.

Abstract: A laser system employing one or more mirror sets having substantially astigmatism-free focusing power sufficient to maintain a desired laser beam diameter, for example, to compensate for thermally-induced distributed lensing. In one class of preferred embodiments, the invention is a high power gas laser system having a folded optical cavity with a periodic intracavity refocusing means to compensate for distributed negative thermal lensing in the hot plasma that comprises the active medium, and thus maintain a substantially constant beam diameter throughout the optical cavity. The periodic intracavity refocusing means preferably includes a corner mirror set (including at least one curved mirror and at least one other mirror) at each corner of the folded optical cavity. In one preferred embodiment, each corner mirror set is a mirror pair including a spherical mirror and cylindrical mirror.

Abstract: Alignment of a birefringent tunable laser gain medium characterized by a first face and a second face cut at Brewster's angle so that a plane of polarization is defined. The gain medium is secured in the optical path by a rotatable member having an axis of rotation that is normal to the Brewster faces of the optical device. Coupled with the rotatable member is a support allowing adjustment of the angular position about the axis of rotation fo the rotatable member. An operator adjusts the angular position of the rotatable member until the C-axis of the gain medium lies in the plane of polarization. Even though the C-axis may not be parallel to the direction of polarization, the depolarization effects of the misalignment are eliminated by proper adjustment of the angular position relative to the plane of polarization. A tunable, solid state laser using the alignment apparatus with a birefringent filter achieves greater linear tuning range.

Abstract: A laser oscillator system which transmits laser input beam pulses through optical diode and into a plurality of time-multiplexed phase conjugate amplifier which sequentially amplify in chronological order subsequent input beam pulses. The optical diode is positioned on the oscillator laser beam pulse axis and is comprised of a polarizer, a half-wave plate which rotates the pulse polarity by 45.degree. in one direction and a Faraday rotator which rotates the pulse polarity 45.degree. in the opposite direction. A plurality of grouped Pockels cells and polarizers are positioned on the oscillator axis past the Faraday rotator. The polarizers route the input beam pulse toward a phase conjugate amplifier when a half-wave voltage is applied to the Pockels cell. Each phase conjugate amplifier has a phase conjugate mirror, at its output for retroreflecting the once amplified input laser beam pulse back therethrough for a second amplification.

Abstract: A method and apparatus which corrects the amplutide variation in the output in an electro-optic modulated laser system (10). Birefringence within the electro-optic crystal (25) causes elliptical polarization of the linearly polarized laser light (22) produced by the laser gain medium (16), in turn causing a loss in the laser output (27). The loss owing to the elliptical polarization is corrected by either applying a D.C. bias from voltage source (30) directly to the electro-optic crystal (25) or by inserting a quarter-wave plate (32) within the laser's resonant cavity.

Abstract: A laser adapted to operate at a constant, predetermined wavelength includes the following elements disposed in order within a laser cavity and aligned along the path of light flow therethrough: a highly reflective rear mirror, a halfwave plate, a Brewster window, an active laser medium, and an output coupler. The halfwave plate is designed to rotate incident light beams by 180.degree. at the predetermined wavelength and to rotate incident light beams by an amount other than 180.degree. at wavelengths other than the predetermined wavelength. In a preferred embodiment, the Brewster window is a thin film polarizer designed for the predetermined wavelength.

Abstract: A linear laser having a dual frequency output is shown where the output frequencies may be varied while maintaining a constant frequency separation. The laser includes a first fully reflective mirror spaced apart from a second partially reflective mirror defining a resonant cavity, a non-reciprocal element disposed within the cavity between the two mirrors, a magnetic field forming device at the non-reciprocal element and means for varying the resonant frequency of the cavity.

Abstract: A Q-switch for a laser having a resonant cavity including an output coupler, a gain medium and a retro-reflecting mirror is mounted in the resonant cavity between the gain medium and the retro-reflecting mirror. The Q-switch comprises a polarizer and a phase retarding element (such as a Pockels cell) which includes a birefringent substrate for inducing a controllable phase retardation in the cavity mode in response to an applied electric field. A tiltable mount supports the phase retarding element so that the lasing axis lies essentially in a plane of the crystallographic axis 45.degree. from the direction of polarization, and lies at an adjustable angle relative to the crystallographic axis. A control circuit supplies an applied electric field within the substrate having a first magnitude in a first state and a second magnitude in a seocnd state. In the first state, the phase retarding element induces 90.degree. rotation in a round trip for the cavity mode.

Abstract: An optical amplifier includes a plurality of amplifiers which are disposed between a first reflective mirror and a second reflective mirror of an optical resonator arranged with the first reflecting mirror and the second reflecting mirror in face-to-face relationship and are adapted to amplify light through induced emission; and a beam combining and separating device which is adapted to combine the light made incident thereupon from the plurality of amplifiers and cause the light to emerge therefrom in the direction of the second reflecting mirror and is also adapted to separate the light from incident thereupon after being reflected by the second reflecting mirror and cause the light to emerge therefrom in the respective directions of the amplifiers. As the combination and separation of the light are repeatedly effected, a beam of light having high energy amplified by the amplifiers is obtained.

Abstract: A method and apparatus for stabilizing the frequency at which a laser cavity oscillates comprising a passive system which provides a plurality or continuum of optical paths of differing lengths. The various paths correspond to differences in mode parameters in the cavity, and involve compensating changes in polarization, beam direction, beam divergence, and the like, in exchange for a constant optical path length in the laser cavity. The unchanging optical path length results in a stable frequency of oscillation despite physical changes in the cavity which might otherwise alter that path length.

Abstract: A room-temperature, solid state laser for producing a CW laser emission cinuously tunable over the approximate spectral range of 1.86 to 2.14 microns is disclosed. In a preferred embodiment, the laser comprises: a diode pump laser for producing a CW pump beam at a preselected wavelength; a laser cavity defined by first and second reflective elements opposing each other on a common axis to form a reflective path therebetween; a laser crystal disposed in the laser cavity, the laser crystal having a host material doped with a concentration of thulium activator ions sufficient to produce a CW laser emission in the range of a plurality of wavelengths determined by the Stark components in the .sup.3 F.sub.4 to .sup.3 H.sub.

Abstract: A laser oscillator/amplifier system in which thermally induced birefringence in the gain media of the oscillator is compensated by thermally induced birefringence in the gain media of the amplifier. The system produces a quality output beam efficiently and with high power density in the preferred polarization. The oscillator cavity is characterized by a high reflector at one end and an output coupler at the second end with an oscillator gain medium exhibiting thermally induced birefringence in between. An amplifier exhibiting thermally induced birefringence which matches the thermally induced birefringence in the oscillator gain medium is mounted to receive the output of the oscillator cavity. A ninety degree rotator is mounted between the oscillator gain medium and the amplifier so that compensation for thermally induced birefringence in the oscillator gain medium is compensated by the matching thermally induced birefringence in the amplifier.

Abstract: An especially inexpensive laser tube is formed having a mirror mount composed of a material which is not matched to the coefficient of thermal expansion of the mirror material and in that the material is either soft soldered or glued on with a glue that develops little gas.

Abstract: A laser beam shaper which provides polarized output with a high spatial quality, utilizing induced stress birefringence. The laser beam shaper in which light resonates along a resonant path defined by reflective surfaces includes a solid state medium, such as a Nd:YAG rod which exhibits thermally induced stress birefringence that is of known, azimuthally independent distribution in planes perpendicular to the resonant path. On either side of the medium, quarter-wave retardation plates are provided which create essentially circular polarization of the resonant light within the medium. Sandwiching the quarter-wave plates and the medium are the first and second polarizing elements, both of which are aligned along the same preferred plane. By inducing stress birefringence in the medium, an output beam is produced. A shape defined by the distribution of the birefringence is provided. With media such as YAG, the shape of the beam is round with high quality.

Abstract: An improved dye laser having a birefringent tuning filter comprised of one or more birefringent plates wherein each plate is oriented at Brewster's angle to the resonant light beam and is an integer multiple of the thickness of the thickness of the first plate characterized by the fact that the thickness of the first plate is chosen using a new tuning relationship so that a single order tuning curve covers a tuning range of interest. This single tuning curve is almost linear throughout the tuning range and has a tuning angle at the center of the range of approximately five degrees. Also, the tuning curve has a slope throughout the tuning range which provides sensitivity of selected wavelength to tuning angle which is neither too great nor too small. A further refinement in the structure is a non birefringent polarizing plate at Brewster's angle which increases the losses imposed upon light passing therethrough which is polarized at other than Brewster's angle.

Abstract: A second harmonic generator having a non-linear optical crystal element for generating a second harmonic laser light. In this second harmonic generator, a birefringent element is inserted into a resonant optical path of a fundamental wave laser light, whereby the second harmonic laser light emitted as an output laser light is stabilized.

Abstract: A high-speed broadband tunable laser system is disclosed. In one illustrated embodiment, a microprocessor-controlled synchronous tunable laser system is disclosed having multiple tuning elements. The tuning elements can be individual birefringent crystals (such as potassium deuterated hydrogen phosphate) which exhibit electro-optic effects when electric field is applied. Two (or more) of such elements provide coarse and progressively finer control over the wavelength and linewidth. The appropriate voltage values for each element can be stored in a random access memory within a controller and retrieved immediately to obtain a desired wavelength within milliseconds without the scanning delays inherent in mechanical systems.

Abstract: A laser resonator generates a polarized output beam with a laser medium exhibiting thermally induced birefringence and a Y-shaped resonant cavity. A lasing axis extends between a first side and a second side of the laser medium, Radiation transmitted out of the first side of the laser medium has its polarization rotated by 90 degrees and is guided back along the lasing axis into the laser medium for a second pass. A polarizer is mounted on the second side of the laser medium for guiding the radiation having a first polarization along a first path and radiation having a second polarization that is 90 degrees from the first polarization along a second path. Both the first path and the second path include the lasing axis of the laser medium and form a Y-shaped resonant cavity. Along the first path, a high reflecting means is provided to reflect the radiation back along the first path.

Abstract: A radiation generator in which substantially all the radiation modes are locked with respect to one another comprises a radiation generating cavity defined by mirrors and a crystal for generating a continuous train of non-transform limited pulses of coherent radiation. An external cavity is positioned in association with the radiation generating cavity whereby radiation may pass in use in both directions between the two cavities. The external cavity is defined by a medium having a non-linear transmission characteristic which may be substantially non-dispersive for radiation from the generating cavity, and/or which has a negative group delay dispersion. The radiation path length is such that pulses fed into the external cavity are fed back to the radiation generating cavity in synchronism with a later pulse from the generating cavity.

Abstract: Apparatus and method are disclosed for providing a variable lens and birefringence compensator (10) adapted to be used within the resonator cavity of a repetitively pulsed, variable rate, solid state laser. A cylindrical body of optical material (12) having a temperature dependent index of refraction is thermally coupled to heat exchange means (14) surrounded by potting material (16) and a heat sink (18) which adds heat to or extracts heat from the exterior surface of the cylindrical body in order to establish radially dependent thermal and stress gradients within the body. The heat exchange means is supplied power through leads (20) from the same source (22) which excites the excitation mechanism of the solid state laser. Heat is infused into or extracted from the compensator body at the same rate at which the flashtube stimulates the laser rod (24) within the laser cavity defined by resonator mirrors (26, 28).

Abstract: A diode pumped Nd:YAG laser is disclosed. The YAG rod is coated on its ends to define an optical resonator containing the YAG rod. The YAG rod is made sufficiently short, i.e., 1 mm, so that it will support only two axial resonant (lasing) modes. The rod is transversely stressed to polarize the two original modes and to excite a third lasing mode orthogonally polarized to the first two modes. The third mode is separated from the first two modes to provide stable, single mode TEM.sub.001 output. The transverse stress is applied by means of a spring clamp made of a material, Be-Cu, having a low temperature coefficient.