An optical probe includes an optical window for transmitting light therethrough, an ultrasonic transducer for applying ultrasonic vibrations to the optical window for cleaning the optical window, and one or more light guides for transmitting light through the optical window to a measurement region and/or receiving light transmitted through the optical window from the measurement region. The ultrasonic transducer is coupled to the optical window via an elongate body adapted to transmit ultrasonic vibrations from the ultrasonic transducer to the window. The light guides communicate with the optical window adjacent the elongate body. An additional lens or light filter may be mounted adjacent the measurement window and/or the window itself may be adapted to incorporate a lens and/or light filter.