Nonlinear Optics in Colloidal Crystals.
We have studied several nonlinear optical phenomena using periodic dielectric structures. We have used colloidal crystals as the nonlinear distributed feedback structure and have found that electrostriction is the largest intensity dependent effect which modifies the transmission of these structures. When the frequency of high intensity light was tuned near Bragg resonance of a face centered cubic colloidal crystal, the transmission exhibited optical power limiting, complex switching behavior and temporal fluctuations in the transmission. Optical power limiting was observed using colloidal crystals comprised of 86 nm diameter polystyrene spheres when the frequency of the laser beam was tuned to the high frequency edge of the stop gap. Optical switching was observed using colloidal crystals made from a suspension of 120 nm diameter spheres. When the frequency of light was tuned to near the low frequency edge of the stop gap, a nonlinear increase in the transmission was observed as the incident intensity was increased. We observed simple and bistable switching when light was tuned deeper into the stop gap. Multistable switching was observed when the frequency of the light was tuned near the high frequency edge of the stop gap. The spatial intensity distribution of the transmitted and reflected beam were modified when the transmission of the structure abruptly changed. A pump-probe experiment was used to measure the transmission spectrum of the colloidal crystal in the presence of a strong pump field. The results from the pump-probe measurements indicate the lattice compresses when the transmission switches to a high state. The results also show that a defect in the lattice may be created in certain cases when switching takes place. Finally, temporal oscillations were observed when the incident intensity was increased above the intensities where optical switching was observed. The frequency of these oscillations was studied as a function of intensity and wavelength.
- Pub Date:
- Physics: Optics