Abstract: A solid-state laser resonator includes a pair of reflectors 4, 5, a bar-like laser medium 6, a plurality of point laser sources 1, 2 and resonator including a plurality of resonator portions. At least one of the paired reflectors 4, 5 has a curved-surface mirror. The laser medium 6 is interposed between the paired reflectors 4, 5. Laser beams 8 emitted from the point laser sources 1, 2 are passed through one of the paired reflectors 4, 5 and irradiated as pumping lights on one end face of the laser medium 6. The resonators include the pair of reflectors, the laser sources 1, 2 and a plurality of thermal lenses. The thermal lenses are formed within the laser medium 6. The resonators produce output laser beam to produce from the other end face of the laser medium 6 through other one of the reflector 5.

Abstract: Method and apparatus for generating a distortion-free, frequency-modulated optical signal, whereby this signal from an optical semiconductor laser driven with a modulating voltage is distorted by the modulating voltage due to a thermally conditioned frequency transfer function of the transmitter for the modulation frequency of the modulating voltage. For generating the distortion-free, frequency-modulated optical signal, the modulating voltage and/or the distorted, frequency-modulated optical signal itself and/or a superimposition signal containing this optical signal is subjected to a distortion that entirely or partially compensates the distortion of this optical signal. This method is simple and, in combination with receivers for the frequency-modulated optical signal, avoids sensitivity losses.

Abstract: The improved longitudinal discharge laser electrode with IR baffle includes an electrode made up of washers spaced along the laser axis in order to form inter-washer spaces for hollow cathode discharge to take place and for IR radiation to be trapped. Additional IR baffles can be placed between the electrode ann the window.

Abstract: A thin absorbing film is bonded onto at least certain surfaces of a solid state laser gain medium. An absorbing metal-dielectric multilayer film is optimized for a broad range of incidence angles, and is resistant to the corrosive/erosive effects of a coolant such as water, used in the forced convection cooling of the film. Parasitic oscillations hamper the operation of solid state lasers by causing the decay of stored energy to amplified rays trapped within the gain medium by total and partial internal reflections off the gain medium facets. Zigzag lasers intended for high average power operation require the ASE absorber.

Abstract: A process for controlling the preconduction current of a laser diode that operates in conjunction with a monitor diode in a control circuit with operational amplifiers, comprising signal processing filters, an electric supply unit such as, e.g., a power source, and a zero crossing detector, where the laser diode (5a) is driven by a linear current ramp signal provided by the supply unit, that the output signal (16) of the monitor diode (15) is differentiated three times, and that, when a zero crossing of the triple-differentiated monitor diode output signal (16) is detected, an optimum current of the current ramp signal is retained by the action of the zero passage detector.

Abstract: The IR baffles placed between the window and the electrode of a longitudinal discharge laser improve laser performance by intercepting off-axis IR radiation from the laser and in doing so reduce window heating and subsequent optical distortion of the laser beam.

Abstract: An electric field absorption light modulation unit includes a light emission device for emitting light and a modulation device for varying a light transmittance thereof of light applied by the light emission device so as to provide the light as a result of modifying thereof. A driving signal generating unit coupled with the electric field absorption light modulation unit generates a driving signal to be applied to the modulation device from an input information signal by making the modulation device vary the light transmittance thereof, and the driving signal generating unit provides the driving signal so that the driving signal in a fluctuation range in which an undesirable level fluctuation may be present, corresponds to a constant working range of the modulation device, the light transmittance thereof staying at a constant value in the constant working range.

Abstract: A semiconductor laser module is provided by silver soldering the holder part of Kovar to the package of Kovar, and then silver soldering the lens holder part of pure iron or a stainless steel to the holder part. The lens holder part has the convergent rod lens fixedly soldered thereto by an Au/Sn solder of a high melting point of 280.degree. C. The semiconductor laser is fixedly soldered onto a stem, with the stem, the optical fiber and ferrule holder being fixedly soldered at positions so that the light emitted from the semiconductor laser is converged by the convergent rod lens at the light incidence end of the optical fiber and the laser light is coupled to the optical fiber. Thus, the convergent rod lens can be fixed with high-melting-point joining means, and a semiconductor laser module for optical communications in which the deterioration of light connection repeatedly generated by heat stress is suppressed can be obtained.

Abstract: A laser diode driving circuit is provided with a constant current source, a first series circuit connected to the constant current source and including a first switching device and a laser diode, and a second series circuit connected so as to constitute a differential circuit in cooperation with the first series circuit and including a second switching device and an impedance device. The laser diode device is driven by turning on and off the second switching device. As the impedance device, a device is used which causes an impedance of the first series circuit obtained when the first switching device is ON and an impedance of the second series circuit obtained when the second switching device is ON to be substantially the same.

Abstract: A method for automatically adjusting an optical axis of a laser resonator. Specifically, the angle of a mirror in a laser resonator is changed in a very small stepwise increments, and the laser output before the very little change is compared to the laser output after the incremental change. If the laser output after the very small incremental change is larger than the laser output before the very small incremental change, the angle is automatically changed by a very small amount in the same direction as the previous increment. If the laser output after the very small incremental change is smaller than the previous laser output measurement, the angle is automatically changed by a very small amount in the opposite direction. Thus the optical axis of the laser resonator is adjusted automatically.

Abstract: A laser having an adjustment device for varying the output power of the laser. The adjustment device has an adjustment element which is switched in by the operator but cuts out automatically. Using a beam splitter, part of the laser beam is directed on to a light-sensitive element in order to determine the laser power. The values of the selected and instantaneous output power are indicated on the display of a display unit. The adjustment element can be switched in using only one hand and, with the adjustment element switched in, the laser power required can be adjusted using only one hand.

Abstract: A quasi-resonant diode drive current source provides high power pulsed current that drives light emitting diodes, and the like. The pulsed output current of the quasi-resonant diode drive current source is sensed, and is regulated by a control loop to a level required by the light emitting diodes. In a specific embodiment of the invention, a zero-current-switched full wave quasi-resonant buck converter is described that provides a high amplitude pulsed output current required to drive light emitting pump diodes used in a solid state diode pumped laser. The use of a quasi-resonant converter as a pulsed current source provides a much higher conversion efficiency than conventional laser current sources. This higher efficiency results in less input power drawn from a power source and cooler operation, resulting in a higher reliability current source.

Abstract: A gimballed optical system within a seeker head includes a relatively low power laser coupled to a relatively higher power laser by way of a flexible fiber optic cable to reduce the mass that must be oscillated in a scan.

Abstract: A gas laser oscillating unit comprises: an electric discharge tube 1 for generating an electric discharge which is to be used as a laser excitation source for laser gas flowing in one direction 17 between an anode 3 and a cathode 2 which are made of a metal material and located at both ends of the electric discharge tube 1, a tube member 22 having a pair of slits 21 for generating a swirl of laser gas upstream of the cathode 2, and a tapered hollow member 23 having a tapered inner surface 23a for squeezing the laser gas stream. The cathode 2 is connected with the tube member 22 through the tapered hollow member 23. At least the inner surface of each of the tube member 22 and the tapered hollow member 23 is made of an alloy material containing aluminum and is processed to form a black alumite layer 31 thereon, wherein the black alumite layer 31 is made from an inorganic material.

Abstract: A laser diode protective circuit for an optical transmission apparatus having a laser diode for converting an information signal into a luminous signal to be output. The laser diode protective circuit includes at least two of the following three circuits: a filter circuit, provided at a preceding stage of the laser diode, for permitting passage of only a predetermined frequency band of the information signal; a detection/interruption circuit for detecting when a signal having a level higher than a predetermined level is supplied to the laser diode, and for temporarily interrupting the signal to be supplied to the laser diode; and a control circuit for controlling an electric power for use in driving the laser diode. A noise component to be introduced into the laser diode contained in the optical transmission apparatus is limited by the filter circuit in terms of frequency, the detection/interruption circuit in terms of time, and the control circuit in terms of electric power, so as to protect the laser diode.

Abstract: An internally folded scalable laser has a gain medium with an internal face nd an external face and at least one internal-fold face subtending an angle which may be about 90.degree.. An output coupler that is partially reflective of the resonator mode is oriented to receive and reflect resonator mode in a direction normal to the internal face to avoid resonator mode astigmatism and to define a folded hemispherically-shaped resonator cavity extending from the output coupler and through an active volume in the gain medium to the external face. A pumping mode source disposed adjacent to the external face is oriented to focus a first pumping mode in a direction normal to the external face in a boom waist at or inside the external face in the folded resonator cavity to define an active volume in the gain medium and to avoid pumping mode astigmatism.

Abstract: The invention relates to a high energy solid-state laser using a new optical pumping device, comprising optical fibers coupled to optical pumping sources of great power and to a laseing medium. The coupling surface through which optical pump energy is transmitted onto the laseing medium is displaced by motor for improved heat dissipation and selective coupling of the pump energy to various resonant cavities.

Abstract: In order to avoid that the thyratron in a conventional laser pulse discharge circuit latches up in its conductive condition, a control circuit is introduced, which ensures that the thyratron is only triggered in intervals where the voltage across the primary coil L1 is decreasing or has reached an oscillation amplitude which is below a predetermined level.

Abstract: An electrical compensation circuit and an optical compensation circuit are provided for compensating for expansion-type and compression-type gain distortion due to the interaction of a laser and an optical amplifier. In the electrical compensation circuit there is provided a linear signal path and a nonlinear signal path. A delay circuit in the linear signal path compensates for a signal delay in the nonlinear signal path. In the nonlinear signal path there is provided an FET and a transformer. A modulation signal applied to the linear signal path and the nonlinear signal path is processed in the nonlinear signal path and combined with the signal in the linear signal path so as to provide a predistorted modulation signal which is substantially equal in amplitude and opposite in phase to the gain distortion in the optical signal at the output of the optical amplifier.

Abstract: For small line width tuning of a laser, especially a pulsed dye laser, a reference beam is uncoupled from the laser resonator (10,18) and directed to a beam position photosensor such as an adjacent pair of photo diodes. A control signal for synchronizing the movements of a grating (10) and an etalon (18) of the laser resonator is derived from a local change of the reference beam in order that synchronism may be achieved in the movement of both the etalon and the grating.

Abstract: A gimballed optical system within a seeker head includes a relatively low power laser coupled to a relatively higher power laser by way of a flexible fiber optic cable to reduce the mass that must be oscillated in a scan.

Abstract: Laser emissions are stabilized at a plurality of frequencies by passage tugh an absorbing medium pumped by light, merged therewith, to an excited energy state corresponding to pumping light frequencies. Error signals are generated in response to detection of intensity of radiation exiting the absorbing medium which deviates from that of the laser emissions at the stabilizing frequencies to correctively adjust resonant cavity length of the laser generator being frequency stabilized.

Abstract: A DC-to-DC converter using an SCR bridge receives a first DC power signal and generates a current pulse train in response thereto. The current pulse train is supplied to a rectifying bridge which generates the second DC power signal in response thereto. A single capacitor means is placed between the leads of the output rectifier bridge to aid the commutation of the SCR bridge.

Abstract: A laser that is capable of producing light from a chosen group of frequencies not adequate or available using a single gas laser is provided. The laser is capable of producing selected and well defined light wavelengths. The laser is also capable of eliminating unwanted frequencies in order to prevent such frequencies from competing with (robbing power from) the desired wavelengths. The laser constitutes a multiple gas laser. A combination of argon and krypton is used. Argon is known to produce a good blue laser beam in the area of 488 nm. Mixed with the argon is krypton. Krypton also produces a blue output at 482 nm and 476 nm. In addition, krypton produces strong outputs in red, yellow, and green wavelengths (647 nm, 568 nm, and 529 nm respectively). Accordingly, access to each of these colors is provided by the argon-krypton in the mixture. Certain light frequencies are unnecessary and undesirable. Elimination of undesirable wavelengths is accomplished primarily through the optics used.

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: A circuit for stabilizing an oscillator having an oscillator output signal includes a long optical fiber delay line which receives an optical version of the oscillator output signal and a phase detector sensing the oscillator output signal and the delayed optical output signal through the long optical fiber. The output of the phase detector is fed back to the oscillator's frequency control input to stabilize the frequency. The phase detector and the delay line are a delay line discriminator, and the length of the optical fiber is selected so as to optimize the discriminator's sensitivity against signal attenuation in the optical fiber, the optical fiber length typically being on the order of 10 kilometers.

Abstract: A method or apparatus for controlling the output pulse of a Q-switched laser. The intensity of laser light within the resonator of a Q-switch laser is sensed. A reference pulse related to a desired laser output pulse shape is compared with the sensed intensity. A variation signal corresponding to differences between the sensed light intensity and the reference pulse is fed to a Pockels cell or Q-switch within the resonator. The Q-switch responds to the variation signal by altering the resonator laser light polarization to maintain the Q-switch laser's output pulse in the desired shape. The reference pulse may be dynamically altered to change the shape of the output pulse.

Abstract: A pulse forming and delivery system 10 is disclosed for forming and deliverying a pulse of electrical energy to a flashlamp 38. System 10 includes a capacitor 14 which is adapted to selectively store electrical energy from a power supply 16 and to transfer this electrical energy to flashlamp 38 when the gate portion of thyristor 12 is open. This gate portion is opened by controller 28. The total amount of light energy emanating from the laser and/or provided to flashlamp 38 is monitored by detector 42 and communicated to controller 22 by means of bus 44. When this total amount has exceeded a desired energy level, controller 22 prevents further electrical energy to be impressed upon switch controller 28 thereby, closing the gate portion of thyristor 12 and preventing any further transfer of energy to flashlamp 38.

Abstract: Extended laser life may be obtained by measuring, with an ammeter AM, the discharge current applied to a laser (either linear or a ring laser gyro RLG), measuring the intensity of the resulting light beam with an intensity monitor IM, calculating the noise with an integrated circuit IC, and maintaining the discharge current at the lowest level possible which is consistent both with maintaining the intensity above the intensity service limit and the noise below the noise service limit.

Abstract: Amplitude or intensity noise in the output of a laser in detuned operation is reduced by application of a frequency dependent transfer function which exploits amplitude-phase coupled noise described by the linewidth enhancement parameter .alpha. by applying an inverse of a replica of the amplitude noise recovered from the phase noise to the laser output. The noise canceling amplitude is applied to the laser output by a filter whose frequency dependent transfer function is related to the inverse of the amplitude-phase noise transfer function of the laser producing the output. The appropriate transfer function may be selected and/or adjusted in response to the magnitude of the amplitude noise. The intensity noise may be reduced by the factor 1/(1+.alpha..sup.2) which may squeeze the intensity noise below normal quantum limits.

Abstract: In response to a source current supply and a sink current supply, a switching circuit selectively forms a current path through which a constant source current from the source current supply flows into a laser in order to turn on the laser and a current path through which a constant source current from the source current supply flows into the sink current supply in order to turn off the laser.

Abstract: In an optical arrangement for amplifying an input lightwave signal by a predetermined amount to a desired output level, an optical amplifier is connected to a loss element. The optical amplifier is pumped by an amount exceeding a nominal amount wherein the nominal amount is the amount of pumping needed to attain the desired output level at the optical amplifier output. By attenuating the signal output from the optical amplifier, the loss element generates an output signal from the optical arrangement at the desired output level. This optical arrangement is characterized by an improved noise performance (noise figure) over standard optical amplifiers.

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: A method and apparatus for automatically maintaining the length of a laser cavity in a laser system in an optimum single length mode regardless of changes of frequency in the dispersive optics feedback, by sensing a group of pointing directions of a laser beam over a determined range of operating conditions, determining the average pointing position of the laser system for the group of sensed pointing directions and adjusting the length of the laser cavity to conform the pointing direction of the laser system to the average pointing direction.

Abstract: An air cooled, flash lamp pumped, solid state laser device wherein heating devices are disposed on the laser rod at both ends to heat and temperature stabilize the laser rod. The solid state, laser rod is longer than the arc length of the flash lamp. The ends of the laser rod can be heated directly by winding heating wire, such as Nichrome, around each end or by applying heat through thermal conductive supports. A feedback loop is provided to maintain temperature of the solid state laser rod, which is preferably Alexandrite, within a desired range of 80.degree. C. to 120.degree. C.

Abstract: A laser apparatus is disclosed which is capable of protecting the laser slab or rod crystal within the laser from damage due to overheating when the laser malfunctions in a manner such that laser output ceases while optical pumping of the laser crystal continues. The laser apparatus includes a laser crystal situated within a laser cavity. The apparatus also includes an excitation lamp for pumping the crystal to generate a laser beam to project along a desired main path. A first sensor senses the cessation of the projection of the laser beam along the desired main path and a second sensor senses the continuing excitation of the excitation lamp. The apparatus further includes a extinguishing circuit for extinguishing the excitation lamp a predetermined amount of time after the cessation of the laser beam such that damage to the laser apparatus due to overheating is avoided.

Abstract: A wavelength-tunable semiconductor laser device presenting a large wavelength-tunable range or a very-high-speed modulating semiconductor laser device having a distributed feedback structure including a diffraction grating as in the case of a DBR laser or a DFB laser incorporates therein a plurality of active layers differing from one another in constituent elements or composition ratio or thickness for reducing spectral line widths, while improving single-mode spectral oscillation characteristics.

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 is described for automatically maintaining the group velocity dispersion (GVD) of a Gires-Tournois interferometer (GTI) as the wavelength of incident light is varied. In the system, the transmission through the GTI is monitored by a photodiode as the wavelength is varied. The transmission through the GTI provides a measure of its GVD. Thus, the output of the photodiode can be used as a control signal for adjusting the GTI in a manner to maintain its GVD at the desired level. The subject system is illustrated in conjunction with a pulsed, tunable, Ti:sapphire laser which is passively mode locked with the optical Kerr effect. The system allows the wavelength of the laser to be tuned over the bandwidth of the gain medium while maintaining a selected level of GVD from the GTI which in turn maintains the desired duration of the pulses. In addition, the GTI is used to compensate for the dispersion effects created by broad band optics in the resonator.

Abstract: A laser source with small output fluctuations due to variations in ambient temperature. The frequency doubler, which has an optical waveguide formed on the substrate of its nonlinear optical crystal, and the laser generator are fixed on the same optical axis within the lens barrel. Moreover, the material used for the lens barrel has a thermal expansion coefficient which is substantially similar to that of the nonlinear optical crystal.

Abstract: A high power TEM.sub.00 mode Nd:YLF solid state laser includes at least two pumped Nd:YLF solid state rods in series within a laser resonator. A spherical lens may be incorporated within the resonator as required for establishing, in concert with the rods and resonator end mirrors, a large intracavity beam diameter at the position of the rods. A cylindrical lens may be provided to compensate for astigmatic thermal focusing of the Nd:YLF rods, or else the rods may be used in pairs, in which case the rods are rotated by 90.degree. about the laser axis with respect to each other, and a half-wave plate is inserted between the rods of each pair to maintain oscillation at a single wavelength.

Abstract: An actively stabilized laser is disclosed which includes a temperature tunable etalon in the laser cavity for single frequency operation. The operation of the laser is actively monitored to detect variations induced by changes in the length of the resonator. These changes tend to cause the frequency of the selected longitudinal mode to shift so that it is no longer aligned with the peak of the transmission curve of the etalon. When this misalignment occurs, operation deteriorates. By monitoring laser performance, the misalignment can be detected and the temperature of the etalon can be changed to realign its transmission peak to the selected mode. In the preferred embodiments, either the laser output power or the current supplied to the laser is monitored. This approach substantially reduces mode hopping. An automatic initialization routine is also disclosed for selecting the starting etalon operating temperature in order to maximize the output power of the laser.

Abstract: An electronics controller for controlling the power supply of a laser operating in a pulse mode is disclosed. The power supply is of the type having resonant DC converter, charging a capacitive storage means with an inverter stage driving the laser discharge tube. The current supplied to the laser discharge tube is monitored. In addition, the voltage of the capacitive storage means is also measured. Set points for the current, the voltage, and on/off are provided to the electronics controller as the comparison points for the controller. Based upon the voltage and current detected, and the set points provided, the controller controls the on/off of the converter and its frequency, and the on/off of the inverter.

Abstract: A method for stabilizing an oscillation frequency separation among a plurality of laser devices wherein a plurality of laser devices are controlled to emit light outputs each having a predetermined frequency so that a frequency separation is stabilized, wherein the plurality of laser devices are divided into a plurality of groups, in each of which the frequency separation is stabilized in accordance with a reference light output of one reference laser device. On the other hand, a plurality of the reference laser devices are controlled to stabilize a frequency separation each other, so that relative frequency separation among the plurality of groups of the plurality of laser devices are stabilized. As a result, a frequency separation of a large number of laser devices is stabilized.

Abstract: A method and device for preventing premature optics burn-out in a laser having a solid gain medium is provided. The invention involves preheating the gain medium by supplying power at a level which is sufficient to set up a thermal lens, yet insufficient to cause substantial production of laser light. In one approach, a simmer routine is overlaid on a ramp routine, so that the power supplied to the gain medium is gradually increased during the warm-up period.

Abstract: Control systems for stabilizing the position of a beam from a laser are disclosed. In one aspect, lateral alignment deviations created by varying thermal effects in a solid state gain medium are compensated. A system is also disclosed which can isolate and the correct both lateral and angular alignment errors.

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: A lighting device comprises a light source, a light reflective cylinder, and a light receiving surface receiving light directly from the light source and another light reflected from the light reflective cylinder. The light reflective cylinder has a shape such that light intensity on the light receiving surface is constant. The light source is a linear source of light. The light receiving surface has a width W and includes a flat surface extending in parallel to the optical axis of the linear source of light. The light reflective cylinder extends continuously from opposite ends of the flat surface and is composed of plates each extending in parallel to the optical axis of the linear source of light and having a very small width.

Abstract: A wavelength-tunable semiconductor laser device presenting a large wavelength-tunable range or a very-high-speed modulating semiconductor laser device having a distributed feedback structure including a diffraction grating as in the case of a DBR laser or a DFB laser incorporates therein a plurality of active layers differing from one another in constituent elements or composition ratio or thickness for reducing spectral line widths, while improving single-mode spectral oscillation characteristics.

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.