The paper is devoted to a numerical analysis of an influence of a pumping beam diameter on output power of optically pumped vertical-external-cavity surface-emitting lasers. Simulations have been carried out for a structure with a GaInNAs/GaAs active region operating at 1.32 urn. Various assembly configurations have been considered. Results obtained show that laser power scaling is strongly affected by thermal properties of the device.
 O. G. Okhotnikov, Ed., Semiconductor Disk Lasers: Physics and Technology. Weinheim: Wiley-VCH, 2010.
 S. Chatterjee, A. Chemikov, J. Herrmann, M. Scheller, M. Koch, B. Kunert, W. Stolz, S. W. Koch, T.-L. Wang, Y. Kaneda, J. M. Yarbor-ough, J. Hader, and J. V. Moloney, “Power scaling and heat management in high-power vecsels,” in Lasers and Electro-Optics Europe (CLEO EUROPE/EQEC), 2011 Conference on and 12th European Quantum Electronics Conference, May 2011.
 S. Lütgen, T. Albrecht, P. Brick, W. Reill, J. Luft, and W. Spth, “8-W high-efficiency continuous-wave semiconductor disk laser at 1000 nm,” Applied Physics Letters, vol. 82, no. 21, pp. 3620-3622, 2003.
 A. Chernikov, J. Herrmann, M. Scheller, M. Koch, B. Kunert, W. Stolz, S. Chatterjee, S. W. Koch, T.-L. Wang, Y. Kaneda, J. M. Yarborough, J. Hader, and J. V. Moloney, “Influence of the spatial pump distribution on the performance of high power vertical-external-cavity surface-emitting lasers,” Applied Physics Letters, vol. 97, no. 19, pp. 191 110191 110-3, Nov 2010.
 T.-L. Wang, Y. Kaneda, J. M. Yarborough, J. Hader, J. V. Moloney, A. Chernikov, S. Chatterjee, S. W. Koch, B. Kunert, and W. Stolz, “Highpower optically pumped semiconductor laser at 1040 nm,” Photonics Technology Letters, IEEE, vol. 22, no. 9, pp. 661-663, May 2010.
 J. M. Hopkins, S. A. Smith, C. W. Jeon, H. D. Sun, D. Burns, S. Calvez, M. D. Dawson, T. Jouhti, and M. Pessa, “0.6 W CW GalnNAs vertical external-cavity surface emitting laser operating at 1.32 urn,” Electronics Letters, vol. 40, no. 1, pp. 30-31, Jan 2004.
 R. P. Sarzała and W. Nakwaski, “Optimization of 1.3 um GaAs-based oxide-confined (GaIn)(NAs) vertical-cavity surface-emitting lasers for low-threshold room-temperature operation,” Journal of Physics: Condensed Matter, vol. 16, no. 31, p. S3121, 2004.
 S. L. Chuang, Physics of Optoelectronic Devices. New York: John Wiley & Sons, 1995.
 L. Piskorski, L. Frasunkiewicz, A. K. Sokol, and R. P. Sarzala, “A possibility to achieve emission in the mid-infrared wavelength range from semiconductor laser active regions,” in Transparent Optical Networks (ICTON), 2014 16th International Conference on, July 2014, pp. 1-4.  A. K. Sokół and R. P. Sarzała, “Numerical analysis of optically pumped VECSELs,” Proceedings of SPIE, vol. 8702, 2013.
 T. Leinonen, Y. A. Morozov, A. Harkonen, and M. Pessa, “Vertical external-cavity surface-emitting laser for dual-wavelength generation,” Photonics Technology Letters, IEEE, vol. 17, no. 12, pp. 2508-2510, 2005.
 M. Wasiak, “Mathematical rigorous approach to simulate an over-threshold VCSEL operation,” Physica E: Low-dimensional Systems and Nanostructures, vol. 43, no. 8, pp. 1439-1444, 2011.
 R. P. Sarzala, L. Piskorski, P. Szczerbiak, R. Kudrawiec, and W. Nakwaski, “An attempt to design long-wavelength (į2 um) InP-based GalnNAs diode lasers,” Applied Physics A, vol. 108, no. 3, pp. 521-528, 2012.
 R. Fehse, S. Tomic, A. R. Adams, S. J. Sweeney, E. P. O’Reilly, A. Andreev, and H. Riechert, “A quantitative study of radiative, auger, and defect related recombination processes in 1.3-um GaInNAs-based quantum-well lasers,” Selected Topics in Quantum Electronics, IEEE Journal of, vol. 8, no. 4, pp. 801-810, Jul 2002.
 R. P. Sarzała and W. Nakwaski, “Carrier diffusion inside active regions of gain-guided vertical-cavity surface-emitting lasers,” Optoelectronics, IEE Proceedings -, vol. 144, no. 6, pp. 421-425, Dec 1997.
 A. Amith, I. Kudman, and E. F. Steigmeier, “Electron and phonon scattering in GaAs at high temperatures,” Phys. Rev., vol. 138, pp. A1270-A1276, May 1965.
 S. Adachi, “GaAs, AlAs, and AlxGa1-xAs material parameters for use in research and device applications,” Journal of Applied Physics, vol. 58, no. 3, pp. R1-R29, 1985.
 W. Nakwaski, “Thermal conductivity of binary, ternary, and quaternary III-V compounds,” Journal of Applied Physics, vol. 64, no. 1, pp. 159166, 1988.
 A. K. Sokoł and R. P. Sarzała, “Comparative analysis of thermal problems in GaAs- and InP-based 1.3-umVECSELs,” Optica Applicata, vol. 43, no. 2, pp. 325-341, 2013.
 Y. S. Touloukian, R. W. Powell, C. Y. Ho, and P. G. Klemens, Thermophysical Properties of Matter Volume 1: Thermal Conductivity: Metallic Elements and Alloys. New York: IFI/Plenum, 1970.
 D. R. Lide, CRC Handbook of Chemistry and Physics. Boca Raton: CRC Press, 2005.
 S. Kasap and P. Capper, Eds., Springer Handbook of Electronic and Photonic Materials. Leipzig: Springer, 2007.
 S. Barman and G. P. Srivastava, “Temperature dependence of the thermal conductivity of different forms of diamond,” Journal of Applied Physics, vol. 101, no. 12, pp. 123 507-8, 2007.
 S. Gehrsitz, F. K. Reinhart, C. Gourgon, N. Herres, A. Vonlanthen, and H. Sigg, “The refractive index of AlxGa1-xAs below the band gap: Accurate determination and empirical modeling,” Journal of Applied Physics, vol. 87, no. 11, pp. 7825-7837, 2000.
 S. R. Adachi, Physical Properties of III-V Semiconductor Compounds, 1st edition. Chichester: John Wiley & Sons, 1992.
 W. K. Tan, H.-Y. Wong, A. E. Kelly, M. Sorel, J. H. Marsh, and A. C. Bryce, “Temperature behaviour of pulse repetition frequency in passively mode-locked InGaAsP/InP laser diode — experimental results and simple model,” Selected Topics in Quantum Electronics, IEEE Journal of, vol. 13, no. 5, pp. 1209-1214, Sept 2007.  T. Kitatani, M. Kondow, K. Shinoda, Y. Yazawa, M. Okai, and K. Uomi, “Extremely large refractive index of strained gainnas thin films,” in Indium Phosphide and Related Materials, 1998 International Conference on, May 1998, pp. 341-344.