Ultrasound-modulated optical tomography uses a well focused ultrasound beam to modulate diffuse light inside soft
biological tissues. This modality combines the advantages of ultrasound resolution with optical contrast. However,
because of the low ultrasound modulation efficiency, the large background of un-modulated photons gives a low
signal-to-noise ratio. Here we report a technique for detection of ultrasound-modulated light using a phase conjugated signal
generated by four-wave mixing in a photorefractive polymer. The experimental results demonstrate the potential of this
method to detect ultrasound-modulated optical signals in a highly scattering media with an excellent signal-to-noise
We report the photorefractive properties of tetraphenyldiaminobiphenyl (TPD) based polymer composites
that have been developed for single pulse laser operation at 532 nm. With an optimized composite, we
demonstrate more than 50% diffraction efficiency using 4 mJ/cm2 single shot writing and 633 nm
continuous wave (cw) beam reading. The present devices showed a 300 μs fast response time. This
reveals the potential for these polymer devices in applications which require fast writing and erasure. Since
the writing pulse-width is in nanosecond time scale, the recording is totally insensitive to vibrations. These
devices can also be used as a stepping stone to realize all-color holography since they are sensitive to both
green (532nm) and red (633nm) wavelengths. The holograms can be written with either of these two
wavelengths and can be read by the same wavelength or the other wavelength with high diffraction
efficiency. This demonstrates that these devices have the advantage of performing two-color holography, a
step closer to a dynamic full-color holographic recording medium.
We propose and demonstrate a novel technique for efficient local fixing of photorefractive polymer hologram using a
laser beam. In the new technique, a CO2 laser beam is used to heat the sample and a local hologram can be fixed easily.
By using glass and sapphire with particular thickness as the substrates for the photorefractive device, the hologram can
be fixed efficiently and at much faster speed. The fixation efficiency can be greater than 80% and the hologram can be
fixed in a few seconds. This technique is critical for dynamic holographic 3D display and holographic data storage.
We have demonstrated an optical novelty filter based on the two-beam coupling effect in photorefractive polymers. The photorefractive polymer composition was optimized for response time and two-beam coupling gain by changing the ionization potential and polarizability of various components. In this study, a photorefractive polymer composition was simultaneously optimized for response time and gain, and employed as a key element in a two-beam coupling novelty filter with a high contrast ratio and a limiting frequency of 14Hz, considerably higher than any previously reported in a two-beam coupling photorefractive novelty filter.