Abstract: A quantic cascade laser amplifier (12) having an active zone (20) includes a stack of raw layers of semi-conductor materials formed in an epitaxial manner on a substrate layer (16) of indium phosphide (InP) or gallium arsenide (GaAs) bearing the active zone (20), and a vertical anti-reflection coating (34) that covers an outlet face (28) of the laser radiation made of materials having given refraction indices and a predetermined thickness so that the entire laser radiation can flow through the outlet face. The anti-reflection coating (34) includes a first layer (36) having a first predetermined refraction index (n1) lower than the predetermined refraction index (nD), and at least a second layer (38) having a second refraction index (n2) higher than the predetermined refraction index (nD), characterised in that the first layer (36) of the anti-reflection coating (34) is made of yttrium fluoride (YF3).

Abstract: Quantum cascade laser especially comprising a gain region (14) formed from several layers (20) which each comprise: alternating strata of a first type (26) each defining a quantum barrier made of AlInAs and strata of a second type (28) each defining a quantum well made of InGaAs, and injection barriers (22), interposed between two of the layers (20). The layers of the gain region (14) each constitute an active region extending from one to the other of the injection barriers (22) which are adjacent to it. The strata (26, 28) are dimensioned such that: each of the wells comprises, in the presence of an electric field, at least a first upper subband, a second middle subband and a third lower subband and that the probability of an electron being present in the first subband is highest in the vicinity of one of the adjacent barriers, in the second subband in the middle part of the region and in the third subband in the vicinity of the other of the adjacent barriers.

Abstract: A quantum cascade laser comprising two electrodes (10, 18) for applying an electric control field and a waveguide placed between the two electrodes and which comprises: a gain region (14) consisting of several layers (20) which each comprise alternating strata (22) of a first type each defining a quantum barrier and strata (24) of a second type each defining a quantum well, and two optical confinement layers (12, 16) placed on each side of the gain region (14). According to the invention, each layer (20) of the gain region (14) is arranged so that the active region has three subbands, the potential differences between them being such that the transition of an electron between the two furthermost emits an energy (EGH, EHJ) corresponding to that needed for the emission of two optical phonons.