Smart photogalvanic running-grating interferometer

Photogalvanic effect sPGEd or anomalous photovoltaic effect is a transport phenomenon producing high electric fields s,100 kV/cmd in ferroelectrics. PGE plays an important role in holographic-grating recording and was recently demonstrated for optical actuation and as high-voltage power supply. In this paper we demonstrate PGE generating highvoltage electrical pulses in atmosphere to apply this effect for optical trapping. Optical trapping is a technique for controlling and manipulating matter on the microand nanoscale. Originally suggested for cooling atomic beams, it has evolved into magneto-optical trapping, and finally arrived as an irreplaceable tool for optical tweezing and for neutral dielectric microparticles manipulation in 1986. The technique has produced a major impact in different fields of optics, such as holographic optical tweezing, photonic structures, and optical trapping in space. In biology, the concept of optical trapping offers a powerful procedure for manipulating biologically relevant particles, unzipping DNA molecules, laser micromanipulation of organic molecules for medical treatment, and for environmental cleansing. The optical field can also be used for microfluidic sorting or arrangement of biological particles. Thus a paradigm for noncontact control of microorganisms in biological as well as of small particles in the physical sciences has emerged. A simple method for trapping and transporting particles is through a slow interference pattern sIPd motion formed by two laser beams. Such a trapping was already demonstrated in both photosensitive laser materials and semiconductors through photoelectron holes and molecular fragments motion. This trapping ssometimes defined as holographic trappingd of charged particles through the generation of holographic photo-emf sRefs. 19 and 20d is a useful tool for the generation of electric current and for material characterization. The IP motion can be implemented by introducing a phase shift between two beams in a Mach– Zender interferometer, using holographic radial diffraction grating or electro-optic modulator sEOMd. However, all the existing methods require an additional power source for IP motion. We introduce theoretically and verify experimentally the conceptually smart interferometer that is suitable for physics and biophysics. An alternative procedure for IP motion, that we suggest, is based on the use of photogalvanic actuator as a mirror in one arm of the interferometer, and does not require an external power source. An experimental implementation of the interferometer is shown in Fig. 1. It consists of two mirrors, one adjustable photogalvanic actuator, based on photorefractive z-cut LN crystal, and a cuvette filled with a biological specimen sshown on insetd. The motion of the “smart” mirror produces the running light IP that traps and carries the biological particles inside the cuvette. It has been shown recently that continuous laser illumination of iron-doped sFe-LNd crystal pro-