*Article* **Focusing of a Laser Beam Passed through a Moderately Scattering Medium Using Phase-Only Spatial Light Modulator**

**Ilya Galaktionov \*, Alexander Nikitin, Julia Sheldakova , Vladimir Toporovsky and Alexis Kudryashov**

Institute of Geosphere Dynamics, Leninskiy Avenue 38, Bld. 1, Moscow 119334, Russia; geospheres@idg.chph.ras.ru or nikitin@activeoptics.ru (A.N.); sheldakova@nightn.ru (J.S.); topor@activeoptics.ru (V.T.); kud@activeoptics.ru (A.K.)

**\*** Correspondence: galaktionov@activeoptics.ru

**Abstract:** The rarely considered case of laser beam propagation and focusaing through the moderately scattering medium was researched. A phase-only spatial light modulator (SLM) with 1920 × 1080 pixel resolution was used to increase the efficiency of focusing of laser radiation propagated through the 5 mm layer of the scattering suspension of 1 µm polystyrene microbeads in distilled water with the concentration values ranging from 10<sup>5</sup> to 10<sup>6</sup> mm−<sup>3</sup> . A CCD camera with micro-objective was used to estimate the intensity distribution of the far-field focal spot. A Shack-Hartmann sensor was used to measure wavefront distortions. The conducted experimental research demonstrated the 8% increase in integral intensity and 16% decrease in diameter of the far-field focal spot due to the use of the SLM for laser beam focusing.

**Keywords:** laser beam focusing; scattering medium; spatial light modulator; Shack-Hartmann sensor
