referring to fig1 , there is shown several different types of color centers which can be produced in ionic crystals , including the f - center depicted by reference numeral 10 . the name f - center comes from the german word for color , farbe . f - centers can be produced by heating a crystal in excess alkali vapor or by x - irradiation . the central absorption band ( the f - band ) associated with f - centers in several alkali halides is well known . the f - center has been identified by electron spin resonance as an electron bound at a negative ion vacancy . the f - center 10 of fig1 is a negative ion vacancy with one excess electron bound at the vacancy . reference numeral 11 refers to a self - trapped hole , which essentially shows two vacancies where two holes are indicated by reference numeral 11 . there is also shown another f - center 12 in fig1 . as one can understand , the lattice vacancies are well known and reference is made to the above - noted patents . one can also understand that the simplest imperfection is a lattice vacancy , which is a missing atom or ion , which is also known as a schottky defect . a schottky defect in a perfect crystal can be created by transferring an atom from a lattice site in the interior to a lattice site on the surface of the crystal . in thermal equilibrium a certain number of lattice vacancies are always present in an otherwise perfect crystal , because the entropy is increased by the presence of disorder in the structure . referring to fig2 , there is shown a graph of energy versus displacement and depicts the energy gap between the ground state depicted by reference numeral 14 and the excited state 15 . this is depicted as it varies with the distance between surrounding anions . it can be seen that the energy of absorption 16 is greater than that of emission 13 . this is due to the shift in energy levels with the relaxation of the crystal after absorption . referring to fig3 , there is shown the energy absorption 17 and emission 18 in a kbr f - center . it can be seen that the energy of emission 18 is significantly lower than the energy of absorption . this means that the wavelength of the emitted light will be longer than that of the absorbed light . the peaks are spread out due to fluctuations in bond lengths at temperature . referring to fig4 , there is shown a table of energies of absorption and emission in many common ionic crystals . as one can see from fig4 , the crystal is depicted in the left - hand column with the cation and anion distance , the exciton energy and various other characteristics depicted . such tables are well known and many examples exist in the prior art . in any event , one can understand from fig1 through 4 how color centers are formed and basically they describe an indication of the nature of such centers . as will be explained subsequently , in the present invention there are two ways in which to create patterns of f - centers using ionic crystals . in the first way , collimated gamma rays are used to expose only certain areas of each crystal to the radiation necessary to produce crystal dislocation and therefore f - centers . the gamma radiation passes through both layers of crystals creating color centers in each crystal at the same location . as will be explained , because of the difference in absorption and emission wavelengths of each layer , the two crystals would activate at different wavelengths . such a device is used to create color center lasers capable of lasing at two unique discrete frequencies . referring to fig5 , there is shown the following structure . reference numeral 20 depicts a substrate upon which is grown a crystal such a nacl or kcl or another crystal as shown , for example , in fig4 . the crystal is grown on substrate 20 by known crystal growing techniques and substrate 20 may consist of silicon , a metal , plastic or another substrate material upon which a crystal could be grown . the substrate is an inorganic material . the ionic crystal thickness is on the order of a few milliinches , but the thickness is not critical . it can be deposited on the substrate by sputtering . on top of the crystal layer 21 is a metal layer 22 which is deposited either by cvd or other metal deposition techniques as sputtering and so on . the metal layer 22 has openings or holes 23 and 23 l . the metal layer is an inert metal as , for example , gold , platinum , or any other inert metal and is very thin as between 0 . 05 to 0 . 2 millimeters . deposited on top of the metal layer 22 is a second layer 24 , which is a thin layer of a different type of ionic crystal , which for example could be lif or naf . the layer 21 absorbs light at a wavelength different than the layer 24 . as seen , deposited on top of layer 24 is another metal layer 25 which has openings 26 , 26 b and 26 c . the openings 26 , as one can see , are in alignment with openings 23 , while opening 26 b is associated with layer 24 and therefore gamma rays 27 , which are directed through opening 26 b , do not in any manner impinge on layer 21 . whereas , for example in the event of gamma rays 27 l enter aperture 26 c and pass through aperture 23 c to impinge upon both layers 24 and layer 21 . as can be seen , gamma rays 28 are absorbed by metal layer 25 l and do not further enter the substrate . as indicated , and as seen in fig5 , the holes 26 and 23 allow gamma rays to pass through . therefore , the gamma rays 27 would pass through appropriate apertures 26 and impinge upon layer 24 . gamma rays will also pass through appropriate apertures 23 to impinge upon layer 21 . gamma rays 27 will pass through aperture 26 and be blocked by the metal layer 23 m to prevent them from passing to layer 21 . in a similar manner , gamma rays 27 r pass through aperture 26 c , to irradiate layer 24 and also impinge upon layer 21 as they pass through aperture 23 . the use of gamma radiation as shown in fig5 will produce the f - centers depicted in fig6 . in fig6 there is shown the laminate device of fig5 after being exposed to gamma rays . f - centers such as 30 , 31 , 32 , 33 and so on are present . essentially , fig6 shows f - centers located at all areas that were exposed to radiation . also shown in fig6 are light beams such as 40 , 41 , 42 and 43 . these light beams , for example , are light of the absorption wavelength of the lower ionic crystal . if the light beams 40 , 41 and 43 are at absorption wavelengths of those of the lower ionic crystal , then the lower ionic crystal based on the f - centers in that layer will emit light as shown by reference numeral 50 . thus , light 40 which emanates and strikes layer 21 causes layer 21 to lase and emit light 50 at the emission wavelength of layer 21 due to the f - center . it is seen that light 41 , which is of the same frequency as light 40 , does not cause layer 24 to lase because of the different absorption frequency . fig7 depicts a same device a s shown in fig6 , except that the light 60 , 60 m and 60 r depicted in fig7 is of the absorption wavelength of the top crystal layer 24 . also shown in fig7 , only the top crystal layer emits light as , for example , rays 61 and 62 , when light 60 impinges thereon . light rays such as 60 r and 60 l which is the same frequency as light 60 impinge upon the metal surfaces 25 and 25 l and thereby do not cause lasing . the lasing is caused because the structure depicted has the access holes such as 26 and 23 to enable light to be directed to either the top ionic crystal 24 or the bottom ionic crystal 21 . referring to fig8 , there is shown still another embodiment of a device where essentially there is depicted a substrate 80 having deposited on a top surface a first ionic crystal layer 81 . deposited on top of first ionic crystal layer 81 is a second ionic crystal layer 82 . both ionic crystals have different absorption wavelengths as indicated above . in the embodiment of fig8 , collimated beams of gamma rays 83 l and 83 r are directed to both crystals at particular areas , which are selected spots . as can be seen , the difference between the structure in fig7 and fig8 is that the metal layers do not exist and therefore there are no particular holes , but a selected area of the device is now irradiated by collimated gamma rays , which essentially cause f - centers to appear . as seen in fig9 , the f - centers 85 and 86 will only appear where the collimated beams are incident . fig9 shows the results of the gamma irradiation of the crystal layers . when light 88 and 88 a of the absorption wavelength of the bottom layer 81 is directed on the crystal , the bottom crystal lases , producing output beam 89 and 89 a . since the wavelength of light is not the absorption wavelength of the top crystal 87 , there is no lasing of the top crystal . however , in fig1 , light 90 and 90 a , which has the characteristic absorption wavelength of the top layer 82 , the top layer 82 produces output beams 91 and 91 a . in this case , the f - centers of the top layer emit laser light 91 and 91 a indicative of the top layer &# 39 ; s emission wavelength . referring to fig1 , there is shown still another embodiment . in fig1 , a substrate 95 has deposited thereon a first ionic crystal layer 96 . deposited on ionic crystal layer is an anion layer 97 . the anion layer , when heated , an ionic crystal with f - centers ( fig1 ). the numerals f designate the f - centers , which are created when needed . as one can ascertain , there are f - centers as 99 a , 99 b and 99 n . these f - centers are distributed throughout the layers and therefore when light , again of a particular frequency indicative of the top layer 98 or the bottom layer 96 is incident upon the device , the device will emit or lase light based on the emission wavelength of the layers . thus , as one can ascertain from the present invention , f - centers are created by collimated gamma rays , which expose only certain areas of each crystal to the radiation necessary to produce crystal dislocation and therefore , f - centers . the gamma radiation passes through both layers of crystals , creating color centers in each crystal at the same location . however , because of the difference in absorption and emission wavelengths of each layer , the two crystals activate at different wavelengths . the device depicted is utilized to create color center lasers capable of lasing at two unique frequencies . the second way of producing patterns of f - centers is by masking each layer with a thin layer of metal . this is depicted , for example , in fig5 , 6 and 7 . a layer of metal is deposited on the first layer of crystal and then etched to form a pattern of holes before the second ionic layer is deposited . a final layer of metal is then deposited over the second layer of crystal . this second layer can also be patterned such that some of the holes coincide with the holes of the first layer and some of them are unique to the second layer . in this layer collimated gamma ray beams can be swept or scanned over various parts of the device . if the beam is aimed at a hole that is in both layers of metal , then both ionic crystals will be exposed and become colored . if the beam passes over a hole that is only in the top layer of metal , then the top crystal will be the only one with color centers at that location . in this way , the bottom crystal layer will have a pattern that is only part of the pattern contained on the top layer . this allows the device to display two different patterns , depending on the wavelength on light incident on the surface . another way of producing the f - centers in the two layers does not involve gamma rays . this is depicted , for example , in fig1 and 12 . it is known that if an ionic crystal is heated in the present of excess anions , f - centers can be formed in the material . in the present device , after each ionic layer is deposited , a thin layer of the anion alone , such as sodium in the case of sodium chloride , is deposited in the top . this material is then heated so that f - centers are formed in the crystal . then the second layer is added and another layer of different anion is deposited and the whole device is heated again . in this case , there is no need for a metal masking layer , as the entire ionic layer will generate f - centers . this technique will be useful in the creating of other layers in the two different lasing frequencies . it is , of course , understood that such a device having two different lasing frequencies is extremely useful and many applications , such as the transmission of information along optical fibers and other uses can be employed as well . the device can be used to create two color displays as reference numerals or other display by scanning with proper light beam . while the above - noted invention was described in terms of specific embodiments , it should be understood by those skilled in the art that many alternate embodiments could be employed as well without departing from the spirit and scope of this invention .