We describe new light-driven actuators based on films of polymer polyvinylidene fluoride, known as PVDF. The actuators employ the photomechanic bending of the polymer film caused by low-power (10 mW and less) laser radiation. The photomechanic effect combines various physical mechanisms, such as thermal expansion, the converse piezoelectric mechanism, and the photovoltaic and pyroelectric mechanisms, while the mechanism of thermal expansion is dominant. The force applied by the actuators to external objects is measured with a torsion balance. It is proportional to the power of laser beam and could be as high as 10(-4) N for a 50-mu m film illuminated with a 10-mW laser beam. We demonstrate mechanical vibrations of a 1 x 7-mm strip actuator at a frequency of 0.3 kHz. As examples of possible applications, a photonic switch and an actuator with a closed-loop motion that could drive the inner workings of a conventional mechanical clock were demonstrated. The proposed actuators have a potential of being used as propulsion components of future light-driven micro/nano systems. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

We describe new light-driven actuator based on films of the polymer polyvinylidene fluoride known as PVDF. The actuator employs the photomechanic effect of bending of the polymer film caused by low power (10 mW and less) laser radiation. The photomechanic effect combines various physical mechanisms, such as thermal expansion, converse piezoelectric along with photogalvanic and pyrolelectric, while the thermal mechanism is prevailing. The force applied by the actuator to external objects was measured with a torsion balance. It is proportional to the power of laser beam and could be as high as 10(-4) N for a 50-micron film illuminated with a 10-mW beam. We demonstrated mechanical oscillations of a 1-mm by 10-mm actuator at a frequency of 0.3 kHz. The frequency could reach 1 MHz and higher for actuators of micron size. The actuators could be easily made of various shapes. Illumination could be in multiple regions of the actuator body with various time delays between laser pulses in different regions. All this can provide a lot of flexibility in terms of the trajectory of mechanical motion. As an example, we demonstrated an actuator with elliptical motion that could drive inner workings of a conventional mechanical alarm clock. The proposed actuator has a potential of being used as a core element of future optical micro- and nanomotors.

Photothermal bending of strips of polyvinylidene fluoride was initiated by a laser beam with a power of a few milliwatts. A bending strip generated a force of 10−4N that propelled a 1 g oscillating wheel of a mechanical clock. The frequency of photomechanical resonance at pulsed illumination was inversely proportional to the length of the strip. The proposed model explained bending as a result of uneven thermal expansion on opposite sides of the strip. The model predicted, in agreement with experiment, that the force is proportional to beam power and does not depend on the shape or position of the beam in the strip.

All-optical actuators based on static or moving holographic gratings could have an advantage over current actuators because of their smaller size, less power and less RF interference. Instead of an ultrasonic wave produced by an electrically driven piezoelectric actuator as in ultrasonic motors, the wave resulted from mechanical deformation of the crystal caused by photo-generated electric charge distribution due to the converse piezoelectric effect. The charge distribution was periodical since it was produced by a holographic grating generated by two interfering coherent laser beams. Surface gratings associated with holographic volume gratings in photorefractive crystals of iron-doped lithium niobate have been studied using diffraction of a reflected probe beam and high-resolution phase-shifted interferometric profilometry. Both techniques show that the surface gratings do in fact exist in the form of periodical corrugations of the same period as that of the volume grating. The maximum amplitude of the surface grating measured by both techniques was close to 6.5 nm. We also demonstrated that the periodical electric forces on the surface were capable of assembling polystyrene microspheres along the fringes of the grating.

Surface gratings associated with holographic volume gratings in photorefractive crystals of iron-doped lithium niobate have been studied using diffraction of a reflected probe beam and high-resolution phase-shifted interferometric profilometry. Both techniques show that the surface gratings exist in the form of periodical corrugations of the same period as that of the volume grating. The maximum amplitude of the periodical surface relief measured by both techniques is close to 6.5 nm. We also demonstrated that the periodical electric forces on the surface were capable of assembling polystyrene microspheres along the fringes of the grating. Large amplitude of the periodic electric field (1.6×104 V/cm) is associated with the photogalvanic effect.

Generating a moving holographic grating in a slab of photorefractive crystal can turn it into a smart optical material making up an optically driven actuator. Actuation occurs as a result of mechanical deformation of the crystal caused by photogenerated electric charge distribution due to piezoelectric effect. The charge distribution is periodical since it is produced by a holographic grating generated by two interfering coherent laser beams. In case of static grating with oscillating amplitude or grating vibrating near the static position the effect results in appearance of a surface acoustic wave or in bending bulk crystal as has been recently demonstrated for BSO. In this paper we focus ourselves on periodical surface deformation moving synchronously with running holographic grating. This running surface wave of deformation is similar to that being used to push a rotor pressed by its surface against a vibrating stator in so-called ultrasonic motors. It can be potentially used in optically driven actuators, which could be small in size (nanometers), less power consuming, and less affected by RF interference. We report on an appearance of a periodical surface deformation in photorefractive crystals of iron doped lithium niobate that is produced by a holographic grating. The amplitude of the deformation is of the order of 10 nm. We also report light-induced mechanical motion of micron-size particles associated with self-diffraction of weak laser beams in strongly absorbing solutions of phthalocyanines. These results might find some applications in new types of all-optical and electrooptical actuators.