Optical tweezers technology is widely used to trap and manipulate particles, and the trapping mechanism generally accepted by researchers is due to the action of photophoretic force. In this paper, infrared microscopic observation of absorbing particles trapped in gaseous medium is first achieved. When the laser power is about 1.0 W, the temperature of trapped toner particles (diameter is about 7 μm) and toluidine blue particles (diameter is from 1 μm to 20 μm) rises by about 14 K, which provides strong evidence for the photophoretic force mechanism. In addition, the periodic oscillation of trapped particles is first observed by both optical microscope and infrared microscope, and the oscillation principle is analyzed.