Optimization of particle trapping and patterning via photovoltaic tweezers: role of light modulation and particle size

Diffractive optical devices produced by light-assisted trapping of nanoparticles

“…It shows seven diffraction orders at angles Ѳn = nλ/Λ that perfectly correlate with those expected for the spatial period, Λ = 20 µm. By using particles of sufficiently small diameter (10-50 nm) grating periods down to around 4 µm can be achieved as previously reported [19]. As an example the diffraction pattern for a grating with Λ = 8.5 µm is also shown in Fig.…”

“…For 1D diffraction gratings we apply a sinusoidal illumination obtained by two beam interference on a X-cut Fe:LiNbO3 substrate [8,19], using the parallel photorefractive configuration with the K-vector along the ferroelectric c-axis. For 2D gratings, we use a twodimensional distribution of light intensity generated by a spatial light modulator (HOLOEYE, LC-R 1080).…”

“…After the pattern fabrication the initial bulk photorefractive charge grating is erased by thermal heating [18] during about 10 min at T ~ 250ºC to avoid its competition with the particle grating. The deposition and light-assisted patterning procedures are described in more detail in [8,19] and [20] for 1D and 2D, respectively. Finally, it is worthwhile remarking that the method can be considered reconfigurable in the sense that the same substrate can be reused by simply removing the particles and repeating the fabrication process.…”

“…It is convenient to use a high light contrast, i.e. m ~ 1, in order to enhance the PV fields and generate a well-defined particle pattern [19]. The periodicity of the final particle patterns coincide with that of the light.…”

Recent Achievements on Photovoltaic Optoelectronic Tweezers Based on Lithium Niobate

“…Initially, the fabricated fringe particle patterns had periods in the range of 50-500 µm that later were reduced down to a few microns. In reference [35] an analysis on this subject is provided. The minimum periodicity recently reported [22] of 2 micrometers was obtained for a fringe pattern of pollen fragments although submicrometric periods should be achievable by using smaller particles.…”