of two different materials and the device has a fabry perot cavity region 14 that contains the active material for simplicity of manufacture the substrate most desirably is a semiconductive gallium arsenide wafer and the two different materials making up the quarter wave layers then may be aluminum gallium arsenide algaas and aluminum arsenide alas the cavity region of this microlaser may be composed of indium gallium arsenide quantum wells with gallium arsenide barriers it will be recognized however that other materials and combinations can be used without departing from the spirit of the invention part 16 of the top reflector is made up of p type gallium arsenide and a pair of current blocking regions 17 and 18 are formed by a deep proton implant to assure appropriate containment of the lasing action as is conventional an active region 19 for the lasing action is thereby defined in keeping with the invention the upper reflector differs from a conventional surface emitting laser structure in that it includes a freely suspended mirror layer 23 of a conductive material such as aluminum it the microlaser the mirror 23 and the remainder of the device can be formed by conventional epitaxial growth techniques such as molecular beam epitaxy mbe or chemical vapor deposition cvd the relative position of layer 23 to the rest of the structure is changeable by the application of an electrostatic field the result of this is that the effective optical distance between the two reflectors making up the cavity is adjustable that is the average position of the constituents of the second reflector relative to the cavity changes with a change in.