I recently acquired the Laser 304 collection (https://www.sanwulasers.com/Green_Red_Violet_304_Laser_pointers/p3911805_15832422.aspx). I am satisfied with the product and I will order from Sanwu again soon. I do however wonder how to properly clean the Laser lens. I can see dust particles on the lens taking an effect on the beam. Is it an acrylic lens or a glass lens ? How do I clean it properly ?