XVI National Symposium on Condensed Matter Physics, Sokobanja 2004 Analysis of Optical Gain of Intersubband Optically Pumped Mid-infrared Laser in Homogeneous Magnetic Field Marko Eric, Vitomir Milanovic Electro-technical faculty Belgrade, University of Belgrade, Belgrade, Serbia and Montenegro Zoran Ikonic and Dragan Indjin School of Electronic and Electrical Engineering, University of Leeds, LS2 9JT, Leeds, United Kingdom Abstract. Optically pumped mid-infrared intresubband lasers in magnetic field are considered. The rate equation model is set up to include electron scattering with acoustic and polar optical phonons in the magnetic field. A strongly non-monotonic gain vs. field dependence is found, with gain peaks occurring at fields which bring appropriate states into resonance with optical phonons, opening additional relaxation paths. These peaks exceed the gain achievable in the structure under zero-field conditions. INTRODUCTION Intersubband semiconductor lasers have been introduced in the 90s for creating laser beam with better qualities then ordinary semiconductor lasers. Among intersubband SC lasers the ones with electron injection as a pump are the most popular ones, but these type of laser has a huge fault, they are quite difficult to produce. In a response to this a new type of intersubband SC lasers have been proposed with the different pump, such as optically pumped intersubband lasers which radiate in mid-infrared domain which is in present days very interesting for industry and technology. Though, this type of laser has to use other laser for the pump, their big side is a great simplification of laser fabrication and design, and this is the main reason for develop of this type of laser. The reason for putting this type of laser in HMF (homogeneous magnetic field) is to attain the discrete energy levels instead of energy subband. With discrete levels the optical gain is going higher for some magnitudes of HMF then without it, and in the same time the laser beam monochromatic and coherency is a lot better then without HMF. To attain discrete energy levels without MF the 3D quantum structure would be needed, the quantum dot (QD) laser. The manufacture of OD laser is a lot more difficult then even quantum cascade laser. The laser structure for optically pumped lasers suggested by [5.] we shell simulate in HMF. THEORETICAL CONSIDARATION The structure considered here has been proposed by [5], and it is based on GaAs-AlGaAs hetero-junction. This structure is periodical and it consists out of highly asymmetrical coupled quantum wells and barrier 20 nm wide. Asymmetrical coupled quantum well (ACQW) is consisting out of two GaAs wells 7.8 nm and 4.9nm wide, and AlGaAs barrier 1.7 nm wide in between. Here, in this structure, there are 3 subbands, lower subband is ground state, and upper two are excited states. Energy deference between the bottom of first excited and ground subband is in resonance with energy of polar optical phonon (36 meV). Optical pumping is being preformed between ground and second excited subband using CO 2 laser. To attain population inversion necessary for lasing it is needed fast liberation of electrons in first excited subband, because lasing is being preformed between second and first excited state. The liberation of electrons from first excited subband is being preformed by nonradiative emission of phonons. Output photons have energy which is lower then the energy of input photons, causing the shift of laser spectrum to the higher wavelengths (mid- infrared domain). 141