Abstract: A novel method and apparatus for suppressing ASE and/or parasitic oscillation modes in a laser is introduced. By roughening one or more peripheral edges of a solid-state crystal or ceramic laser gain media and by bonding such edges to a predetermined electromagnetic absorbing material arranged adjacent to the entire outer surface of the peripheral edges of the roughened laser gain media, ASE, parasitic oscillation modes and/or residual pump energy can be effectively suppressed.

Abstract: A high power solid-state non-regenerative optical amplification system (100) for amplifying a pulsed optical beam, includes a first optical amplification crystal (C1) and a second optical amplification crystal (C2) for amplifying the optical beam; optical pumping elements for longitudinal pumping amplification crystals (C1, C2); reflective optical elements (M?1, M?2, . . . , M?17) suitable for reflecting the optical beam so that the optical beam makes a total number of N sequential passes through the amplification crystals (C1, C2), wherein N is an integer and N>4. The reflective optical elements (M?1, M?2, . . . , M?17) are placed in a configuration suitable for alternatively interleaving the sequential optical beam passes through the 1st crystal (C1) and through the 2nd crystal (C2). A solid-state laser including the amplification system, and a method for amplifying a pulsed optical beam in a two-crystal multi-pass non-regenerative amplification system are also disclosed.

Abstract: There is provided a light source apparatus including at least a excitation light source and a photocoupler, a light source medium formed of one kind of a single, rare-earth element doped fiber that is excited by the excitation light source and has two terminals, and an output end formed of an optical fiber, the light source apparatus being characterized in that an optical component having at least one of reflection, branching or attenuation function is provided in anywhere of an optical circuit from the light source medium to the output terminal and that it is possible to output lights of different wavelengths derived from different spontaneous emission light peaks that are generated from rare-earth element ions added to the rare-earth element doped fiber, and that at least one of the lights to be obtained is visible light.

Abstract: A surface emitting laser diode includes a ring-shaped first semiconductor layer including an n-type clad layer, a ring-shaped active layer provided on the first semiconductor layer, and a ring-shaped second semiconductor layer which is provided on the active layer and includes a p-type clad layer and a grating layer including grating units continuously arranged in a circumferential direction, each grating unit including a plurality of regions having different refractive indices and being adjacent to each other in the circumferential direction.

Abstract: The invention relates to a passively triggered microchip laser (1) formed by a cavity closed by an input mirror (4) and an output mirror (5), characterised in that the cavity includes deflection means (9, 10, 11, 12, 13) designed to deflect a light beam (14) between the input mirror (4) and the output mirror (5).

Abstract: Embodiments disclosed herein relate to a laser die. The laser die includes a base epitaxial portion, a mesa portion, and first and second facets, wherein at least one of the first and second facets is flared such that an area of the facet is increased. Embodiments disclosed herein also relate to a high-speed laser. The high-speed laser includes a substrate, an active region positioned above the substrate, a mesa positioned above the active region, and one or more facets, wherein at least one of the one or more facets includes a flared portion configured to increase an area of the facet.

Abstract: To suppress the amplification of spontaneous emission light in a principal plane width direction to thereby suppress a gain in directions other than a beam axis direction and output a high-power laser, in a solid-state laser element of a plane waveguide type that causes a fundamental wave laser beam to oscillate in a beam axis direction in a laser medium of a flat shape and forms a waveguide structure in a thickness direction as a direction perpendicular to a principal plane of the flat shape in the laser medium, inclined sections 12 are provided on both sides of the laser medium, the inclined sections 12 inclining a predetermined angle to reflect spontaneous emission light in the laser medium to a principal plane side of the flat shape, the spontaneous emission light traveling in the beam axis direction and a principal plane width direction as a direction perpendicular to the thickness direction.

Abstract: A heat capacity laser having a solid lasing medium, at least one pumping source that is able to emit a pumping radiation, and an optical cavity that can be characterized by having: at least one device able to homogenize the pumping radiation, a doped lasing medium having a body with a first and a second end and being stretched in the length by more than 6 cm and whose height in cross section is less than its stretching in the length of the lasing medium. The doping concentration in the lasing medium may vary axially. Also either the cavity can have beam forming optics and the doping concentration of the lasing medium is radially uniform, or the cavity can have no beam forming optics and the lasing medium has a doping concentration that may vary radially.

Abstract: The present invention provides a nano particle phosphor with superior luminous characteristic formed using nitride semiconductor material, a method of manufacturing the phosphor with high production yield, and a light emitting device using the phosphor. The phosphor is formed of a columnar crystal having a diameter of at most 3 nm, a light emitting region and a light absorbing region are defined in the columnar crystal, and the light emitting region and the light absorbing region are adjacent to each other along a longitudinal direction of the columnar crystal.

Abstract: A laser amplifier includes a laser active slab with a source of pump power to amplify an input laser beam, the laser active slab including a block of laser active material having opposed lateral faces defining a wedge lateral dihedral angle specified to minimize parasitic amplified spontaneous emission. The laser amplifier may include one or more external mirrors highly reflecting at the lasing wavelength positioned and oriented to provide for zig-zag passes through the gain sheet for the input laser beam to yield a multi-pass-amplified laser beam. The source of pump power may be one or more laser diode bars and microlenses producing a gain sheet in the laser active slab.

Abstract: The invention relates to a waveguide laser or amplifier material comprising a silica glass host material, one or more rare earth elements in total concentration CRE at. %, one or more network modifier elements selected from the group of tri- or penta-valent atoms of the periodic table of the elements in total concentration CNME at. %, wherein the ratio of atomic concentrations of the modifier elements to that of the rare earth elements CNWCRE is larger than or equal to 1, and wherein the total atomic concentration of rare earth and the tri-valent network modifiers, such as aluminium and/or boron, is substantially equal to the atomic concentration of the penta-valent network modifier, such as phosphorous. Such materials exhibit reduced risk of photo darkening.

Abstract: The invention concerns a device for longitudinal pumping of an amplifying laser medium comprising at least one laser diode capable of emitting at least one laser beam, means for focusing said laser beam onto said amplifying laser medium and means for collimating said laser beam capable of generating a collimated laser beam. The invention is characterized in that said focusing means comprise at least one mirror, said mirror being arranged such that said collimated beam is reflected towards the amplifying medium.

Abstract: Aspects of the present invention are directed to the use of optical gain structures that include alternating layers of gain medium and transparent heat conductors in which the gain medium itself functions as a correction optic. The gain medium changes to an optimum or desired shape because of the thermal changes occurring as the materials of the optical gain structure(s) reach a desired optical output condition. At the desired optical output conditions, the gain medium conforms to a desired shape. The desired shape may be, for example, that of an optical surface of a transparent heat conductor. By designing the initial shape of the gain medium such that the physical contact with the transparent heat conductor is maximized at the desired optical output conditions, conductive heat transfer between the gain medium and heat conductor(s) is maximized at the desired optical output condition.

Abstract: A tunable laser is provided, including: a multiple ring resonator that is formed by coupling ring resonant elements having different optical path length from each other; an input/output-side waveguide connected to one of the ring resonant elements; a reflection-side wave guide connected to another one of the ring resonant elements; a PLC substrate on which the multiple ring resonator, the input/output side waveguide, and the reflection-side waveguide are formed; a high reflection film provided to the reflection-side waveguide; an SOA connected to the input/output-side waveguide; film heaters and a phase control region of the SOA for changing the resonant wavelength of the multiple ring resonator; and a light-receiving element for detecting the resonant wavelength of the multiple ring resonator in a thru port of a directional coupler.

Abstract: A surface emitting semiconductor laser device, having at least one monolithically integrated pump radiation source (20), in which the pump radiation source (20) has at least one edge emitting semiconductor structure (9) that is suitable for emission of electromagnetic radiation whose intensity profile transversely with respect to the emission direction (z) of the semiconductor structure follows a predeterminable curve. Such a surface emitting semiconductor laser device emits electromagnetic radiation having a particularly good beam quality.

Abstract: Several methods are used in novel ways with newly identified and viable parameters to decrease the peak transition energies of the pseudomorphic InGaAs/GaAs heterostructures. These techniques, taken separately or in combination, suffice to permit operation of light emitting devices at wavelengths of 1.3 ?m or greater of light-emitting electro-optic devices. These methods or techniques, by example, include: (1) utilizing new superlattice structures having high In concentrations in the active region, (2) utilizing strain compensation to increase the usable layer thickness for quantum wells with appropriately high In concentrations, (3) utilizing appropriately small amounts of nitrogen (N) in the pseudomorphic InGaAsN/GaAs laser structure, and (4) use of nominal (111) oriented substrates to increase the usable layer thickness for quantum wells with appropriately high In concentrations.

Abstract: A semiconductor laser device capable of reducing the threshold current and improving luminous efficiency and a method of fabricating the same are obtained. This semiconductor laser device comprises a semiconductor substrate having a principal surface and a semiconductor element layer, formed on the principal surface of the semiconductor substrate, having a principal surface substantially inclined with respect to the principal surface of the semiconductor substrate and including an emission layer.

Abstract: A laser amplifier includes a laser active slab with a source of pump power to amplify an input laser beam, the laser active slab including a block of laser active material having opposed lateral faces defining a wedge lateral dihedral angle, opposed longitudinal faces, and opposed parallel transverse faces, the wedge lateral dihedral angle specified to minimize parasitic amplified spontaneous emission. The source of pump power may be one or more laser diode bars and microlenses producing a gain sheet in the laser active slab. The lateral faces may include optical coatings highly transmitting at a wavelength of the pump power and highly reflecting at a lasing wavelength to provide a folded path for the input laser beam though the gain sheet.

Abstract: A laser discharge, where the laser discharge can be formed by electrodes and at least one sidewall in a manner allowing a more compact structure than previously provided. Protrusions in the electrodes allow easier laser starts, and sectional sidewall(s) allow easier fabrication of sidewall(s), decreasing manufacturing costs.

Abstract: A laser system, which is used in material processing to produce a radiation line of small width and uniform high intensity in the longitudinal direction, produces radiation that has different mode numbers M2 perpendicular to the propagation direction.

Abstract: It is an object of the present invention to provide a method that can provide regions having different thicknesses of a laminated body containing an organic compound with a light-emitting property in the same element and also can apply an electric field uniformly in all the regions of the element without depending on the thickness of the laminated body containing an organic compound with a light-emitting property. One laser element of the present invention has a laminated body containing an organic compound with a light-emitting property between two electrodes, and the laminated body includes a mixed layer of a metal oxide and an organic compound, which has a thickness distribution. The laser element emits light having different wavelengths in regions having different thicknesses of the mixed layer of a metal oxide and an organic compound, by applying voltage between two electrodes to feeding a current.

Abstract: A process for fabricating lasers capable of emitting blue light wherein a GaN wafer is etched to form laser waveguides and mirrors using a temperature of over 500° C. and an ion beam in excess of 500 V in CAIBE, and wherein said laser waveguide has inwardly angled sidewalls.

Abstract: The basic gain medium enclosure for laser devices comprises two parallel lateral mirrors which geometrically define the extent of the gain medium enclosure and which allow the formation of lateral stationary sinusoidal waves.

Abstract: A distributed feedback laser having a conjugated dendrimer as the active lasing component, and a method for patterning conjugated dendrimers.

Abstract: Devices for generating a laser beam are disclosed. The devices include a silicon micro ring having at least one silicon optical waveguide disposed at a distance from the micro ring. The radius and the cross-sectional dimension of the microring, the cross-sectional dimension of the waveguide, and the distance between the micro ring and the waveguide are determined such that one or more pairs of whispering gallery mode resonant frequencies of the micro ring are separated by an optical phonon frequency of silicon. Methods of manufacturing a lasing device including a silicon micro ring coupled with a silicon waveguide are also disclosed.

Abstract: An intrinsic GaAs waveguide layer is formed on a p-type AlGaAs cladding layer, a quantum dot active layer is formed further thereon. An n-type AlGaAs cladding layer is formed on the center portion of the quantum dot active layer. Thus-configured semiconductor laser is allowed to successfully suppress the area of the p-n junction plane to a small level, and to obtain a high level of reliability, because there is no need of processing the center portion of the quantum dot active layer, contributive to laser oscillation.

Abstract: A laser apparatus has a multipath solid-state slab laser rod and an excitation source that excites it, and uses a solid-state slab laser rod that has a trapezoid or parallelogram-shaped cross section along the optical path, that is provided with six or more faces and that has a light amplifying effect or a nonlinear optical effect. The light that is incident to the laser rod is totally reflected at the incident-light end face and exit end face of the laser rod, passes back through the interior of the laser rod a plurality of times, e.g., three times, and then exits. For light amplification, excitation light is irradiated from the side face. In addition, for nonlinear optical effects, the z-axis of a nonlinear optical crystal is disposed so as to be orthogonal to the plane of the optical path, and the temperature of the solid-state slab laser rod is kept at the phase-matching temperature.

Abstract: A slab laser amplifier with parasitic oscillation suppression has a plurality of angled pump faces related to one another in order to decrease likelihood of parasitic oscillations, with internal beam incidence angles at total internal reflection that alleviate need for reflective coatings. No polished surfaces of gain material comprising the amplifier are parallel to one another. A beam path within the gain material is such that all incident angles of the beam path upon the two main faces and the common end face are greater than a critical angle required for total internal reflection, thereby alleviating need for reflective coatings. Based on an index of refraction of the gain material, and based on a diameter of the laser beam, dimensions of the gain material are selected to maximize beam overlap in a pumped volume of the gain material.

Abstract: As a composite laser rod capable of satisfying the positional stability and output stability of a laser beam, a laser rod in which a laser active element is doped is intimately inserted into a hollow portion of a non-doped ceramic pipe that has a crystal structure the same as the laser rod followed by baking so as to remove a gap and strain at an interface between the laser rod and the ceramic pipe after the baking further followed by polishing a surface of the ceramic pipe to form a ceramic skin layer, and thereby a composite laser rod is formed. In the composite laser rod, an influence due to fluctuation in the cooling capacity of cooling water or a heat sink is averaged by a non-doped skin layer, temperature fluctuation of the laser rod is suppressed, and an influence of vibration from the cooling water or a cooling fan can be suppressed.

Abstract: A spherical laser includes a transparent or semi-transparent outer spherical vessel having an internal cavity, an amplifying medium in the cavity, and means to excite the amplifying medium. The sphere is provided with a partially reflective coating to act as a spherical optical resonator. Excitation of the amplifying medium produces an optical gain. When the gain exceeds cavity losses and threshold conditions are met, lasing is supported. This creates a three-dimensional, spherically radiating emission, emulating a point source. The output is radially diverging, but is harnessed by enclosing the sphere within a mirrored ellipse to image the output to a point, or within a mirrored parabola to columinate the emission. A concentric, reflective inner sphere may be disposed in the cavity, with the amplifying medium lying between the two spheres. A voltage potential is applied between the spheres to excite the medium.

Abstract: A square micro-cavity laser with an output waveguide comprises: a substrate; a resonator, which has a square shape and is fabricated on the substrate; a stripe output waveguide, which is fabricated on the substrate and is connected to the midpoint of one side face of the resonator; wherein the area of the resonator or the stripe output waveguide is less than that of the substrate.

Abstract: A method is described to improve and produce purer Cr4+-doped laser materials and lasers with reduced co-incorporation of chromium in any other valence states, such as Cr3+, Cr2+, Cr5+, and Cr6+. The method includes: 1) certain crystals of olivine structure with large cation (Ca) in octahedral sites such as Cr4+:Ca2GeO4, Cr4+:Ca2SiO4, Cr4+:Ca2GexSi1-xO4 (where 0<x<1), and/or 2) high-temperature solution growth techniques that enable the growth of the crystals below the temperature of polymorphic transitions by using low melting point solvent based on oxide, fluoride and/or chloride compounds. Purer Cr4+-doped laser materials are characterized by a relatively high concentration of Cr4+-lasing ion in crystalline host that makes these materials suitable for compact high power (thin disk/wedge) NIR laser applications.

Abstract: An optically active element, such as a photonic crystal, is formed by creating a matrix (1) in which an optically active material is dispersed, and generating one or more void structures (2, 3) in the matrix. The matrix (1) may comprise polymer dispersed liquid crystal. The void structures (2, 3) may be generated by laser ablation. Properties of the optically active element may be tuned by thermal effects, or via the application of electric, magnetic, or polarised electromagnetic fields. The element may be adapted for use in beam steering, fluid detection, tunable lasers, polarisation multiplexing, and optical switching.

Abstract: An improved tube solid-state laser (SSL) is provided utilizing diode pumping, microchannel cooling, optics, and/or new coating and bonding processes. In one example, an amplifier module for the SSL includes a tube of laser gain material, a first substrate and a second substrate including microchannels adjacent an interior and exterior surface of the tube, respectively, and a plurality of diode bars arranged exterior to the second substrate. Advantageously, thermal lensing effects, birefringence, bifocussing, and alignment problems associated with typical tube SSLs are eliminated or reduced while providing high beam quality and high average power levels.

Abstract: In a symmetrically stable optical resonator, a first reference plane is set at an arbitrary position between the end face (102), opposing a partial reflector (2), and the neutral point (101) of a rod type solid state laser medium (1), and an aperture (5) having a diameter substantially equal to that of the rod type solid state laser medium (1) is arranged at a position optically symmetric to the reference plane with the partial reflector (2) as a neutral point using a relay lens (6) and a coupling lens (7) arranged between the aperture (5) and an optical fiber (8), the first reference plane is transfer-relayed onto the incident end face of the optical fiber (8), and the aperture (5) is transferred onto the coupling lens (7) through the relay lens (6).

Abstract: A light source device includes a plurality of light emission sections disposed in parallel with an interval, wherein the interval for the light emission sections near each end portion in an array of the light emission sections is narrower than the interval near a center portion in the array.

Abstract: Corner pumping method and gain module for high power slab laser are disclosed. In one embodiment, said method comprises directing a pump light from one or more pump light sources each consisting of a high power diode array and its coupling system into a laser slab through prior cut slab corners of said laser slab without restriction to the incident angle or the polarization state of the pump light, wherein said laser slab includes an undoped circumambient portion and one or more doped central portions; propagating said pump light within the laser slab by total internal reflection (TIR), wherein said pump light firstly pass said undoped circumambient portion, secondly pass said doped central portion, thirdly pass said undoped circumambient portion again, and fourthly take inner reflection at the surface of said undoped circumambient portion, and by repeating these steps, achieve multi-pass absorption; and substantially absorbing the pump light during propagating.

Abstract: A semiconductor laser comprises two optical cavities, each comprising an optical waveguide bounded by two partially reflecting elements. The two optical waveguides are disposed on a substrate to form a substantially V-shaped geometry with substantially no cross-coupling at the open end and a predetermined cross-coupling at the closed end for achieving an optimal single-mode selectivity of the laser. The first cavity has a length such that its resonant wavelengths correspond to a set of discrete operating channels. The second cavity has a slightly different length so that only one resonant wavelength coincides with one of the resonant wavelengths of the first cavity over the operating spectral window. The lasing action occurs at the common resonant wavelength. In operation, at least a portion of the optical waveguide in each of the first and the second cavities are forward biased to provide substantially equal round-trip optical gains.

Abstract: A solid state pump cavity comprising a laser rod encased by diffusion bonding inside an outer cladding. The outer cladding provides the ability to efficiently conduct heat away from the laser rod. The outer cladding is also configured to absorb spontaneous laser radiation that would otherwise be re-amplified by the laser rod. Diffusion bonding of the outer cladding to the laser rod forms a seamless optical boundary between the outer cladding and the laser rod. An alternative embodiment of the pump cavity comprises multiple segments of laser rod and outer cladding assemblies coupled together with undoped sections that are diffusion bonded to the ends of the laser rod and outer cladding assemblies.

Abstract: An optical structure that reduces the effects of spontaneous emissions from the active region of a laser. An optical structure includes optimizations to reduce the effects of spontaneous emissions. The optical structure includes a VCSEL with top and bottom DBR mirrors and an active region connected to the mirrors. The optical structure further includes a photodiode connected to the VCSEL. One or more optimizations may be included in the optical structure including optically absorbing materials, varying the geometry of the structure to change reflective angles, using optical apertures, changing the reflectivity of one or more mirrors, changing the photodiode to be more impervious to spontaneous emissions, and using ion implants to reduce photoluminescence efficiency.

Abstract: An optical semiconductor device includes a semiconductor laser chip, a base for mounting the semiconductor laser chip and a solder layer sandwiched between the top surface of the base and the bottom surface of the semiconductor laser chip. The semiconductor laser chip is warped in upward convex shape.

Abstract: In a first embodiment, the invention makes use of a Neodymium doped YAG (Nd: YAG) gain medium placed in an optical resonant cavity formed by two mirrors. Power extraction is maximized for a specific laser cavity. In particular the concave curvature on the rod ends contributes a negative lensing component to modify the strength of the thermal lens. In a second embodiment the present invention uses an amplifier rod medium with curved ends to act as lensing elements to collect emission from the laser gain medium and/or oscillator described in the first embodiment of the invention. The combination of thermal lens and curved rod ends produces a lensing effect which allows light to be directly coupled from a laser. In addition, variation of the input pump power allows for control of the thermal lens formed within the amplifier rod.

Abstract: The present invention relates to a microdisk laser with a unidirectional generation property, and more particularly, to a microdisk laser designed in the form of a triangle, wherein the incident angles of portions of a laser beam at two upper sides of the triangle are greater than a critical angle to cause total reflection, so that the laser beam generates with directionality toward the base of the triangle. To this end, in the microdisk laser with the unidirectional generation property, the laser takes the shape of a triangle with two upper sides and the base and the two upper sides have their lengths greater than or equal to that of the base. Respective vertexes of the triangle or some of the vertexes are curved, and incident angles of portions of a laser beam at the two upper sides of the triangle are greater than a critical angle to cause total reflection, so that the laser beam generates with directionality toward the base of the triangle.

Abstract: An optical semiconductor device includes a semiconductor laser chip, a base for mounting the semiconductor laser chip and a solder layer sandwiched between the top surface of the base and the bottom surface of the semiconductor laser chip. The semiconductor laser chip is warped in upward convex shape.

Abstract: Provided are an optical active device and optical module using the same The optical active device includes first face through which light received emitted, second face facing the first face third face adjacent the first face and the second face, and fourth face facing the third face which width between the first face and the second face equal greater than distance between the third face and the fourth face

Abstract: A thin layer of ionic crystal is grown on a substrate. The crystal could be any type of ionic crystal, such as sodium chloride or potassium chloride. The crystal is a pure form of the chosen compound and may contain contaminants which would shift the wavelength of created color centers. On top of the first crystal layer, a second thin layer of a different type of crystal is deposited, such as lithium fluoride or sodium fluoride. When these two layers are radiated with gamma rays, they will each form color centers at the spots radiated. Because of the difference in crystalline properties of the two different ionic crystal centers, their color centers would be at different wavelengths. Each of the two separate ionic crystals will emit light at different characteristic wavelengths when illuminated at their unique absorption frequencies. Each layer can be made to lase separately.

Abstract: Laser light generating solutions are provided that use one or more light emitting diodes to optically pump a laser light generating structure. The laser light generating structure can include organic or inorganic laser material. The light emitting diodes can be located on the same substrate as the laser light generating structure or on a separate substrate that is connected to the substrate with the laser light generating structure. Various other features can be included to enhance the optical pumping and/or enable electrical pumping of the active structure when it includes an inorganic laser material.

Abstract: The present invention provides a semiconductor optical device 1 that includes a photodiode capable of monitoring front light of the light-emitting device. The optical device 1 includes a photodiode 3, which is formed on a substrate 7 and has an absorption layer 9 and a semiconductor layer 11, and an optical waveguide 5 also formed on the substrate 7. The optical waveguide 5 includes, in addition to the active layer 13, two semiconductor layers 15 and 17. A portion of the light from the active layer 13 enters the photodiode 3 reflected by the end surface 5a of the waveguide 5 and the rest portion of the light passes through the end surface 5a and outputs therefrom. In the present invention, the photodiode 3 and the waveguide 5 are integrally formed on the substrate 7.

Abstract: A laser beam source has a laser element provided with a thin crystal disk as a laser active medium. The laser beam source has improved mechanical stability and improved thermal contact with respect to a cooling element on the flat side of the crystal disk that is disposed opposite the cooling element. A cooling disk is disposed between the crystal disk and the cooling element.

Abstract: In the present invention, methods and apparatus for making efficient cladding pumping fiber lasers is disclosed. In particular, new fiber cladding geometry and new method of coupling pumping laser into an optical fiber are disclosed. Both aspects of the present invention will facilitate the realization of high-efficiency and high-power fiber lasers. In the present invention, cladding boundary geometry structures that can prevent the formation of local modes are disclosed. Besides the cladding geometry, methods for efficient coupling of diode lasers into a laser fiber for high power injection are also disclosed. Essentially, the new methods make it possible to transmit diode laser beams for a long distance with substantially the same brightness.