Abstract:
A semiconductor laser includes a multilayer semiconductor laser heterostructure including at least one active layer of a II-VI semiconductor material and is optically pumped by one or more indium gallium nitride (InGaN) diode-lasers. Group II elements in the II-VI semiconductor material are zinc, cadmium, magnesium, beryllium, strontium, and barium. Group VI elements in the II-VI semiconductor material are Sulfur, Selenium, and Tellurium. In one example of the laser an edge emitting heterostructure includes two active layers of zinc cadmium selenide, two waveguide layers of zinc magnesium sulfoselenide, and two cladding layers, also of zinc magnesium sulfoselenide. Proportions of elements in the cladding layer material and the waveguide layer material are selected such that the waveguide layer material has a higher bandgap than the material of the waveguide layers. In another example, a two dimensional array of InGaN diode-lasers is arranged to optically pump a one dimensional array of II-VI edge-emitting heterostructure lasers.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to semiconductor lasers. The invention relates in particular to semiconductor lasers grown from II-VI semiconductor materials and emitting in a blue region of the visible electromagnetic spectrum.  
       DISCUSSION OF BACKGROUND ART  
       [0002]     One potential application for semiconductor lasers is in the illumination of color display devices. In any such device wherein it was desired to provide an accurate color display, it would be necessary to provide at least one semiconductor laser emitting red light, at least one other semiconductor laser emitting green light and at least one further semiconductor laser emitting blue light.  
         [0003]     Most commercially available blue-light emitting diode-lasers are made from indium gallium nitride (abbreviated InGaN), a II-V semiconductor having a general formula In x Ga 1-x N, where x is equal to or greater than 0.0 and less than or equal to 1.0. The lasers can be made to emit at a particular wavelength in a spectral range from about 380 nanometers (nm) in the ultraviolet region of the electromagnetic spectrum to about 460 nm in the blue region of that spectrum by selecting an appropriate value for x.  
         [0004]     The blue region of the spectrum is defined as having a spectral range extending from about 425 nm (purplish blue) to about 490 nm (greenish blue). Accordingly, InGaN diode-lasers provide can provide light in only in the shortest 50% of the blue region of the spectrum. It would be advantageous to have a diode-laser capable of emitting light in at least the remaining 50% of the blue region of the spectrum.  
         [0005]     Diode-lasers grown from II-VI semiconductor materials such as zinc sulfoselenide ZnS x Se 1-x  and Zn x Cd 1-x Se (where x is equal to or greater than 0.0 and less than or equal to 1.0) are capable of providing light at wavelengths in a range from about 460 nm in the blue region of the spectrum to about 530 nm in the green region of the spectrum. These lasers, unfortunately, have been found to have relatively short lifetimes, for example less than 1000 hours. It is generally believed that the short lifetime is due to the growth of color centers in the II-VI material originating from doping sites in the material. Doping of the material is necessary to provide the p and n conductive layers which provide the “diode” of the diode-laser. The color centers develop as a result of the passage of current through the diode-laser. A lifetime of less than 1000 hours is at least an order of magnitude shorter than would typically be required for a diode-laser to be commercially viable. There is a need for a blue-light emitting, II-VI semiconductor laser that does not have the limited lifetime problem of prior-art II-VI semiconductor diode-lasers.  
       SUMMARY OF THE INVENTION  
       [0006]     In one aspect, a semiconductor laser in accordance with the present invention comprises a multilayer semiconductor laser heterostructure including at least one active layer of a II-VI semiconductor material having a formula A x B 1-x C y D 1-y , where x is equal to or greater than zero and less than or equal to one, y is equal to or greater than zero and less than or equal to one, where A and B are selected from a group of group II elements consisting of (Zn, Cd, Mg, Be, Sr, and Ba), and where C and D are selected from a group of group VI elements consisting of (S, Se, and Te). The laser includes an InGaN semiconductor light-emitting device arranged to optically pump the laser heterostructure.  
         [0007]     In one embodiment of the inventive laser, the multilayer semiconductor laser heterostructure is a surface-emitting heterostructure including two mirror structures and a gain structure including a plurality of the active layers spaced apart by spacer layers, also of a II-VI semiconductor material. The two mirrors form a laser resonator with the gain structure being located in the resonator.  
         [0008]     In another embodiment of the inventive laser, the multilayer semiconductor laser heterostructure is a surface-emitting heterostructure includes one mirror structure and a gain structure including a plurality of the active layers. A separate mirror is spaced apart from the gain structure and arranged to form a laser resonator with the gain structure being located in the resonator.  
         [0009]     In yet another embodiment of the inventive laser, the heterostructure is an edge emitting heterostructure. Reflective facets of the heterostructure form a laser resonator. The InGaN semiconductor light emitting device includes a linear array of diode-lasers. The array of InGaN diode-lasers is spaced-apart from the heterostructure and aligned with a longitudinal axis of the laser resonator. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The accompanying drawings, which are incorporated in and constitute a part of the specification, schematically illustrate a preferred embodiment of the present invention, and together with the general description given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the present invention.  
         [0011]      FIG. 1  schematically illustrates one preferred example of an external cavity, InGaN diode-laser pumped, surface-emitting, II-VI semiconductor laser in accordance with the present invention.  
         [0012]      FIG. 2  schematically illustrates one preferred example of an InGaN diode-laser pumped, monolithic, surface-emitting, II-VI semiconductor laser in accordance with the present invention.  
         [0013]      FIG. 3  schematically illustrates details of one example of a multilayer semiconductor heterostructure including a mirror-structure surmounted by a gain structure in the laser of  FIG. 1 .  
         [0014]      FIG. 4  schematically illustrates one preferred embodiment of an InGaN diode-laser pumped, edge-emitting II-VI semiconductor laser in accordance with the present invention.  
         [0015]      FIG. 5  schematically illustrates details of one example of a multilayer semiconductor heterostructure in the laser of  FIG. 4 .  
         [0016]      FIG. 6  is a three-dimensional view schematically illustrating another preferred embodiment of a linear array of InGaN diode-laser pumped, edge-emitting II-VI semiconductor lasers in accordance with the present invention, including a planar waveguide arrangement for transporting pump light beams from a two dimensional array of InGaN diode-lasers to pump an array of edge-emitting II-VI semiconductor lasers.  
         [0017]      FIG. 7  schematically illustrates one example of an InGaN diode-laser array pumped, edge-emitting II-VI semiconductor laser in accordance with the present invention including an optical system projecting light from the InGaN diode-laser array to form a uniform strip of light on a II-VI semiconductor heterostructure the uniform strip defining the edge-emitting semiconductor laser. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Referring now to the drawings, wherein like components are designated by like reference numerals,  FIG. 1  schematically illustrates one embodiment  20  of a II-VI semiconductor laser in accordance with the present invention. Laser  20  includes a surface-emitting semiconductor heterostructure  22  including a mirror structure  24  surmounted by a gain-structure  26 . Heterostructure  22  is in thermal contact with a substrate, heat sink, or heat spreader  28 . Substrate  28 , optionally, may be a substrate on which the heterostructure is grown.  
         [0019]     Gain structure  26  includes a plurality of active layers of a II-VI semiconductor material having a formula A x B 1-x C y D 1-y , where x is equal to or greater than zero and less than or equal to one; y is equal to or greater than zero and less than or equal to one; where A and B are selected from a group of group II elements consisting of (Zn, Cd, Mg, Be, Sr, and Ba); and where C and D are selected from a group of group VI elements consisting of (S, Se, and Te). The selection of materials for A, B, C, and D and the values of x and y, inter alia, determines the emitting (lasing) wavelength of laser  20 . Examples of gain structure  26  and mirror structure  24  are presented hereinbelow. A concave mirror  32  forms a laser resonator  34  with mirror structure  24  of heterostructure  22 .  
         [0020]     Pump light is supplied by a InGaN light-emitting device  38 . Light-emitting device  38  preferably includes an InGaN diode-laser or an array of InGaN diode-lasers. InGaN light-emitting device  38 , alternatively, may include a plurality of InGaN light-emitting diodes (LEDs). Light delivered from light-emitting device  38  is directed by mirrors  40  and  42  along a path  44  into gain structure  26 , as indicated by solid arrowheads P. Pump light P is absorbed in the gain structure and optically pumps (energizes) the gain structure. In response to the optical pumping of gain structure  26 , laser radiation circulates in the resonator generally along a longitudinal resonator axis  37  as indicated by open arrowheads F. Mirror  32  is partially transparent to the wavelength of the laser radiation and allows the laser radiation to be delivered from resonator  34  as output radiation.  
         [0021]      FIG. 2  schematically illustrates another embodiment  21  of a II-VI semiconductor laser in accordance with the present invention. Laser  21 , is optically pumped by light from a InGaN light-emitting device  38 . Laser  21  includes a surface-emitting semiconductor heterostructure  23  including a mirror structure  24  surmounted by a gain-structure  26 . Gain structure  26  is surmounted by a second mirror structure  30 . Mirror structures  24  and  30  form a very short (only a few micrometers long) resonator  35  including the gain structure  26 . Mirror structure  30  is partially reflective and partially transmissive for the emitting wavelength of gain structure  26  and highly transparent, for example, greater than about 95% transparent, for the wavelength of the pump light P. Optical pump light from InGaN light-emitting device  38  is delivered to gain structure  26  through mirror structure  30 . Laser output radiation is delivered from resonator  35  through mirror  30 .  
         [0022]     Referring now to  FIG. 3 , one preferred II-VI semiconductor multilayer gain structure  26  of heterostructure  22  includes a plurality of active (quantum-well) layers  50  of a II-VI semiconductor material zinc cadmium selenide having a formula Zn x Cd 1-x Se. Layers  50  preferably have a thickness of about 150 nm or less. The layer thickness is exaggerated, relative to that of other layers in  FIG. 3 , for convenience of illustration. The value of x is selected according to the desired emission (laser radiation) wavelength. Active layers  50  are spaced apart by pump-light-absorbing spacer-layers  52  of another II-VI semiconductor material, zinc magnesium sulfoselenide, having a formula Zn r Mg 1-r Se s S 1-s , where 0.0≦r≦1.0, and 0.0≦s≦1.0. Each layer  50 , and an adjacent layer  52 , form a layer pair  54  having a total optical thickness of about one-half wavelength at the emitting wavelength. Gain structure  26  is completed by a cap layer  56 , also of Zn r Mg 1-r Se s S 1-s . Cap layer  56  preferably has a thickness of about one-half wavelength at the emitting wavelength. However, as this layer does not separate active layers, it may have some different thickness.  
         [0023]     A preferred number of layer pairs, i.e., a preferred number of active layers  50 , is between about 10 and 20. Values of r and s in the material of a spacer layer  52  are selected to provide a desired level of absorption of pump light P, and, accordingly, will depend, among other factors, on the wavelength selected for the pump light. It is possible, albeit time taking in practice, to systematically change the vales of r and s such that the absorption of layers  52  increases with increasing proximity of the layers to mirror structure  24 . This can be arranged such that most or all pump light is absorbed in the gain structure, and little or no pump light reaches mirror structure  24 .  
         [0024]     In the example of  FIG. 3 , mirror structure  24  is formed from a plurality of layer, pairs  58  each thereof including a layer  60 , and a layer  62  having a refractive index less than that of layer  60 . Layer  60  is formed from zinc magnesium sulfoselenide having a composition Zn u Mg 1-u Se v S 1-v  where 0.0≦u≦1.0, and 0.0≦v≦1.0. Layer  62  is formed from zinc magnesium sulfoselenide having a composition Zn w Mg 1-w Se z S 1-z , where 0.0≦w≦1.0, and 0.0≦z≦1.0. Preferably, layers  60  and  62  each have an optical thickness of about one-quarter wavelength at the emitting wavelength of gain structure  26 .  
         [0025]     Mirror structure  24  preferably has a reflectivity greater than 99% at the emission wavelength of gain structure  26 . About fifteen layer pairs  58  may be required to provide a reflectivity greater than 99% with the exemplified refractive index values.  
         [0026]     In one example of heterostructure  22 , for emitting at 460 nm, layer  50  preferably has a composition ZnSe (x=1.0), and spacer layers  52  preferably have a formula Zn 0.87 Mg 0.13 Se 0.85 S 0.15 . Mirror layer  60  preferably has a composition Zn 0.9 Mg 0.09 Se 0.88 S 0.12  and mirror layer  62  preferably has a composition MgSe 0.14 S 0.86 . In another example of a heterostructure  22 , for emitting at 488 nm, layer  50  preferably has a composition Zn 0.85 Cd 0.15 Se, and spacer layers  52  preferably have a formula ZnSe 0.925 S 0.075 . Mirror layer  60  preferably has a composition ZnSe 0.94 SO 0.0.06 , and mirror layer  62  preferably has a composition MgSe 0.14 S 0.86 . In yet another example of a heterostructure  22 , for emitting at 532 nm, layer  50  preferably has a composition Zn 0.7 Cd 0.3 Se; and spacer layers  52  preferably have a formula ZnSe 0.91 S 0.09 . Mirror layer  60  preferably has a composition ZnSe 0.94 S 0.0.06 , and mirror layer  62  preferably has a composition MgSe 0.14 S 0.86 .  
         [0027]     In a preferred method of growing a heterostructure  22 , gain structure  26  is grown on a GaAs substrate (not shown) beginning with cap layer  56  and mirror structure  24  is then epitaxially grown on the gain structure. After such mirror structure has been grown deposited, mirror structure  24  of heterostructure  22  can be bonded to a substrate  28  in the form of a heat sink, or a diamond or sapphire heat spreader, and original epitaxial growth substrate removed from gain structure  26  by selective etching.  
         [0028]     The epitaxial mirror structure of  FIG. 3  is preferred for optimally transferring heat developed in the heterostructure into substrate  28 . Such a mirror structure, however, can become highly stressed during the growth process and can cause the heterostructure to be mechanically unreliable. Mirror structure  24 , however, can then be formed on the gain structure by vacuum evaporation (non-epitaxial growth) of alternating, quarter-wave optical thickness layers of high and low refractive dielectric materials, such as tantalum oxide (Ta 2 O 5 ) and silicon dioxide (SiO 2 ), respectively. Only about eight layer pairs  58  of these materials would be required to achieve a reflectivity greater than 99%. The lesser total thickness of the dielectric mirror structure compared with the epitaxial structure of  FIG. 3  compensates somewhat for the poorer thermal conductivity of the dielectric materials compared with the semiconductor materials. Whichever of the above-described mirror structures  24  is used to form a heterostructure  22 , that heterostructure can be converted to the heterostructure  23  of the monolithic laser  21  of  FIG. 2  by vacuum depositing high and low refractive index dielectric layers to form mirror  30  on gain structure  26 .  
         [0029]      FIG. 4  schematically illustrates yet another embodiment  70  of a II-VI semiconductor laser in accordance with the present invention. Laser  70  includes an edge emitting heterostructure  72 . Heterostructure  72 , here schematically depicted in a basic form, includes a lower cladding (carrier confinement) layer  76 , a lower waveguide (optical confinement) layer  78 , an active (quantum-well) layer  80 , an upper waveguide layer  82  and an upper cladding layer  84 . Active layer  80  is formed from a II-VI semiconductor material as defined above for active layers  50  of laser  20 . It should be noted here that the terminology “upper” and “lower” as applied to layers of heterostructure  72  are used merely for convenience of description and do not necessarily relate to gravitationally determined “up” or “down”.  
         [0030]     On one end or facet of heterostructure  72  is a reflective coating  86  configured to provide maximum reflectivity, for example, greater than 99% reflectivity at the emitting wavelength of the heterostructure. On an opposite end (facet) of heterostructure  72  is a (optional) partially reflective, partially transmissive coating  88 . Those skilled in the art to which the present invention pertains will recognize that should coating  88  be omitted the uncoated facet will have a reflectivity of about 21% due to the relatively high refractive index (about 2.7) of the layers of the heterostructure.  
         [0031]     Heterostructure  72  is optically pumped by an InGaN light-emitting device  38 , here, in the form of linear array  90  of diode-lasers  92 . The diode-lasers are electrically pumped via electrodes  94 . Diode-lasers  92  in array  90  are in thermal contact with a common heat sink  95 . Diode-lasers  92  are spaced apart from each other in array  90 , and array  90  is spaced apart from heterostructure  72  such that light beams from adjacent ones of the diode-lasers overlap in the slow axis (the X-axis, as depicted in Cartesian coordinate system  97 ). This is indicated by short-dashed lines  96 . An elongated cylindrical microlens  112  has positive dioptric power in the fast axis of array  9  (the Y-axis, as depicted in Cartesian coordinate system  97 ) and zero dioptric power in the slow axis of array  90 . Microlens  112  is aligned with the length thereof parallel to the slow axis of array  90  and spaced apart from the array such that light from the diode-lasers is collimated. As the microlens has zero optical power in the slow axis, the divergence of light from the diode-lasers in the slow axis is unchanged. This allows the separation of array  90  and heterostructure  72  to be adjusted to achieve a desired slow axis overlap while maintaining a constant beam dimension in the fast axis.  
         [0032]     The diode-laser array  90  illuminates a “stripe”  75  of heterostructure  72  having a width (designated in  FIG. 4  by long-dashed lines  100 ) about equal to the fast axis beam width of the diode-lasers at microlens  112 . The coatings (reflective facets)  86  and  88  form an elongated, gain guided, waveguide laser resonator in the stripe region. Laser radiation is emitted from an emitting aperture (hatched area  77 ) having a width about equal to the stripe width, as defined by short-dashed lines  102 , and a height about equal to the total thickness of quantum well layer  80  and upper and lower waveguide layers  82  and  78 . The resonator has a longitudinal axis (not explicitly shown) parallel to the Z-axis of Cartesian coordinate system  71  of  FIG. 4 . The emitted laser radiation has a relatively narrow divergence, for example about 10° half-angle, in the slow axis (X-axis of coordinate system  71 ) as indicated by rays  104 . The emitted laser radiation has a relatively wide divergence, for example about 35° half-angle, in the fast axis (X-axis of coordinate system  71 ) as indicated by rays  104 . Here, it should be noted that coordinate system  97  is specific to diode-laser bar  90  and emitters  92  thereof, while coordinate system  71  is specific to heterostructure  72  and emitter  77  thereof.  
         [0033]      FIG. 5  schematically illustrates one preferred II-VI semiconductor multilayer edge-emitting heterostructure  72 A for above-described laser  70 . Heterostructure  72 A is similar to heterostructure  72  with an exception that heterostructure  72 A includes two quantum well layers  80  separated by a barrier layer  79 . Layers  80  are formed from Zn x Cd 1-x Se. Layers  50  preferably have a thickness of about 150 nm or less. The layer thickness is exaggerated in  FIG. 5  for convenience of illustration. The value of x is selected according to the desired emission (laser radiation) wavelength as discussed above with reference to surface-emitting heterostructure  22 . Barrier layer  79  has about the same thickness as that of the quantum well layers and is formed from zinc magnesium sulfoselenide having a composition Zn p Mg 1-p Se q S 1-q , where 0.0≦r≦1.0, and 0.0≦s≦1.0.  
         [0034]     Upper and lower waveguide layers  82  and  78  preferably have a thickness of about 500 nm and are formed from zinc magnesium sulfoselenide having a composition Zn u Mg 1-u Se v S 1-v , where 0.0≦r≦1.0, and 0.0≦s≦1.0. Values of u and v are selected such that the waveguide layers have a higher bandgap than that of the quantum well layers.  
         [0035]     Upper and lower cladding layers  84  and  76  preferably have a thickness of about 1.0 micrometers (μm) or greater and are formed from zinc magnesium sulfoselenide having a composition Zn x Mg 1-x Se y S 1-y , where 0.0&lt;r&lt;1.0, and 0.0&lt;s&lt;1.0. Values of x and y are selected such that the cladding layers have a higher bandgap than that of the waveguide layers.  
         [0036]     In one example of heterostructure  72  for emitting at 460 nm, quantum well layers  80  preferably have a composition ZnSe (x=1.0); waveguide layers  78  and  82  preferably have a composition Zn 0.87 Mg 0.13 Se 0.85 S 0.15 ; and cladding layers  76  and  84  preferably have a composition Zn 0.78 Mg 0.22 Se 0.79 S 0.21 . In another example of a heterostructure  72  for emitting at 488 nm, quantum well layers  80  preferably have a composition Zn 0.85 Cd 0.15 Se; waveguide layers  78  and  82  preferably have a composition ZnSe 0.94 S 0.06 ; and cladding layers  76  and  84  preferably have a composition Zn 0.91 Mg 0.09 Se 0.88 S 0.0.12 . In yet another example of a heterostructure  72  for emitting at 532 nm, quantum well layers  80  preferably have a composition Zn 0.7 Cd 0.3 Se; waveguide layers  78  and  82  preferably have a composition ZnSe 0.94 S 0.06 ; and cladding layers  76  and  84  preferably have a composition Zn 0.91 Mg 0.09 Se 0.88 S 0.0.12 .  
         [0037]      FIG. 6  schematically illustrates another preferred embodiment  130  of a linear array of InGaN diode-laser pumped, edge-emitting II-VI semiconductor lasers in accordance with the present invention. Laser  110  includes an elongated II-VI edge-emitting semiconductor heterostructure  72 A. Heterostructure  72 A has a layer structure similar to that structure described above with respect to  FIG. 5  and to laser  70  of  FIG. 4 .  
         [0038]     Pump light is supplied by an InGaN light emitting device  38  including linear arrays  90 A-E of InGaN diode-lasers  92 . Diode-lasers in each array are mounted on common heatsink  95 . Each diode-laser bar  90  is provided with a cylindrical microlens  112  arranged to collimate fast axis rays from diode-lasers  92  in the diode-laser array. Each diode-laser array is intended to irradiate a particular stripe  75  on heterostructure  72 A.  
         [0039]     An array  132  of strip or planar waveguides  134  serves to transport light from the InGaN diode-laser bars  90  to heterostructure  72 A. Input ends  134 A of the planar waveguides are parallel to each other, and are spaced apart to correspond to the fast-axis spacing of the diode-laser bars. Waveguides  134  are variously shaped along the length thereof such that exit ends  134 B are spaced apart according to a desired spacing of stripes  77  and individual emitters  77  in heterostructure  72 A. Proximate the output end  134 B of each waveguide  134  is a cylindrical microlens  136  configured and arranged to collimate light emitted from the waveguides. Here, five separate collimated beams  140  (indicated in  FIG. 6  by single arrows only) pump the five spaced-apart parallel elongated regions or “stripes”  75  of heterostructure  72 A.  
         [0040]     Waveguides  134  are preferably formed from ultraviolet (UV) grade fused silica. Individual waveguides can be cut from a ground and polished sheet of a desired thickness. Edges, entrance faces and exit faces of the waveguides can be polished by temporarily blocking together a number of the cut waveguides, polishing the edges, and the entrance and exit faces of the waveguides, then dismantling the block to release individual polished waveguides. The individual polished waveguides can then be shaped longitudinally, if necessary. By way of example, shaping of a waveguide can be accomplished by heating the waveguide to a softening temperature and “slumping” the waveguides onto a mandrel including a surface having the desired waveguide shape.  
         [0041]     One advantage of using a waveguide to transport radiation from an InGaN diode-laser bar to pump an edge-emitting, II-VI semiconductor laser in accordance with the present invention is that the waveguide will tend to homogenize the light output from the InGaN diode-laser bar along a direction corresponding to the X-axis (slow axis) thereof. This will tend to provide uniformity of pumping along the Z-axis (longitudinal axis) of the II-VI semiconductor laser. The actual uniformity obtained will depend, inter alia, on the width and spacing of emitting apertures of the InGaN diode-laser bar and the length, width and height of the waveguide.  
         [0042]     Another means of achieving uniformity of pumping along the Z-axis of an edge-emitting, II-VI semiconductor laser in accordance with the present invention is to project the light from an InGaN diode-laser bar using an optical system configured to project a line or strip of light in which light from each individual emitter in the bar contributes to illuminating the entire length of the projected strip. A brief description of an embodiment of the inventive edge-emitting, II-VI semiconductor laser optically pumped in this manner is set forth below with reference to  FIG. 7   
         [0043]     Here, a laser  142  includes an InGaN light-emitting device  38 , in the form of an InGaN diode-laser array  90  including a plurality of diode-lasers  92 . The diode-laser bar is mounted on a heat sink  95 . Diode-laser array  90 , in this example, includes four diode-lasers but this should not be construed as limiting the present invention.  
         [0044]     The X, Y and Z-axes (fast, slow and propagation axes respectively) of diode-laser bar  90  are indicated in  FIG. 7  generally by a coordinate system  97 . An optical system  144  combines light from all diode-lasers in diode-laser bar  90  to form a line or strip of light  75  (indicated in  FIG. 9  as a hatched area bounded by dotted lines  100 ) on heterostructure  72 . Light strip  75  is aligned with the longitudinal axis (Z-axis or propagation direction) of an emitter  77  in heterostructure  72 .  
         [0045]     Optical system  144  has X, Y, and Z-axes (fast, slow, and longitudinal axes respectively) corresponding to the X, Y, and Z axes of diode-laser bar  90 . It should be noted that these axes correspond, generally, to the Z, X and Y axes of emitter  77  of heterostructure  72  as in other above-discussed embodiments of the inventive edge emitting lasers. Rays traced through optical system in the X-Z plane thereof (slow axis rays) are designated by solid lines. Rays traced through optical system in the Y-Z plane thereof (fast axis rays) are designated by dashed lines.  
         [0046]     Optical system includes a positive cylindrical lens  112  that collimates fast-axis rays from diode-lasers  92  of the diode-laser bar. An array  146  of positive cylindrical lenses  148  includes one cylindrical lens  148  for each diode-laser  92  in diode-laser bar  90 . The cylindrical lenses focus slow-axis rays through an intermediate pupil (not shown) of optical system  144  between lens array  146  and a negative cylindrical lens  150 . These rays are then diverging on reaching lens  150 . Lens  150  causes collimated fast-axis rays from lens  112  to diverge. The diverging fast-axis rays are focused by a combination of a positive, spherical doublet lens  152  and a positive cylindrical lens  154  and define the width of strip  75  (the height of the strip in terms of optical system  144 ). The diverging slow-axis rays are collimated by a combination of lenses  152  and  154  and define the length of strip  75 .  
         [0047]     It should be noted here that light-strip projecting optical systems in other configurations are known in the art to which the present invention pertains. Accordingly, only sufficient description of optical system  144  is provided herein to illustrate optically pumping the inventive II-VI semiconductor laser with a line or strip of light projected by such an optical system. A detailed description of an optical system similar to optical system  144  is provided in U.S. patent application Ser. No. 10/667,675, filed Sep. 22, 2003, the complete disclosure of which is hereby incorporated by reference. The diverging fast-axis rays are focused by a combination of a positive, spherical, doublet lens  152  and a positive cylindrical lens  154 . The focused fast-axis rays define the width of strip  75  (the height of the strip in terms of optical system  144 ).  
         [0048]     In summary, the present invention is described above in terms of preferred embodiments thereof. The invention however, is not limited to the embodiments described and depicted. Rather the invention is limited only by the claims appended hereto.