switchable-acoustic-optical-resolution-photoacoustic-microscopy-for

Switchable Acoustic and Optical Resolution Photoacoustic Microscopy for <em>In Vivo</em> Small-animal Blood Vasculature Imaging

Photoacoustic microscopy (PAM) is a fast-growing invivo imaging modality that combines both optics and ultrasound, providing penetration beyond the ...

Nanyang Technological University

We study the shrinkage in acrylamide based photopolymer by measuring the Bragg detuning of transmission diffraction gratings recorded at different slant angles and at different intensities for a range of spatial frequencies. Transmission diffraction gratings of spatial frequencies 500, 1000, 1500 and 2000 lines/mm were recorded in an acrylamide based photopolymer film having 60 ± 5 μm thickness. The grating thickness and the final slant angles were obtained from the angular Bragg selectivity curve and hence the shrinkage caused by holographic recording was calculated. The shrinkage of the material was evaluated for three different recording intensities 1, 5 and 10 mW/cm2 over a range of slant angles, while the total exposure energy was kept constant at 80 mJ/cm2. From the experimental results it can be seen that the shrinkage of the material is lower for recording with higher intensities and at lower spatial frequencies.

Study of the shrinkage caused by holographic grating formation in acrylamide based photopolymer film.

An acrylamide based photopolymer doped with pure silica MFI-type zeolite (silicalite-1) nanoparticles has been characterized for holographic recording purposes. The concentrations of the silicalite-1 nanoparticles in the photopolymer layers were 1, 2.5, 5 and 7.5 wt. %. The inclusion of silicalite-1 nanoparticle in the photopolymer has resulted in an increase of the diffraction efficiency by up to 40%, and decrease of the shrinkage from 1.32% to 0.57%. The best results were obtained in layers doped with 5 wt. % silicalite-1 nanoparticles.

Nanozeolites doped photopolymer layers with reduced shrinkage.

Shrinkage of photopolymer materials is an important factor for their use in holographic data storage and for fabrication of holographic optical elements. Dimensional change in the holographic element leads to a requirement for compensation in the reading angle and/or wavelength. Normally, shrinkage is studied at the end of the polymerization process and no information about the dynamics is obtained. The aim of this study was to use holographic interferometry to measure the shrinkage that occurs during holographic recording of transmission diffraction gratings in acrylamide photopolymer layers. Shrinkage in photopolymer layers can be measured over the whole recorded area by real-time capture of holographic interferograms at regular intervals during holographic recording using a complimentary metal-oxide-semiconductor camera. The optical path length change, and hence the shrinkage, are determined from the captured fringe patterns. Through analysis of the real-time shrinkage curves, it is possible to distinguish two processes that determine the value of shrinkage in the photopolymer layer. These processes are ascribed to monomer polymerization and crosslinking of polymer chains. The dependence of shrinkage of the layers on the conditions of recording such as recording intensity, single or double beam exposure, and the physical properties of the layers, such as thickness, were studied. Higher shrinkage was observed with recordings at lower intensities and in thinner layers. Increased shrinkage was also observed in the case of single beam polymerization in comparison to the case of double beam holographic exposure.

Shrinkage during holographic recording in photopolymer films determined by holographic interferometry.

Photoacoustic microscopy (PAM) is a scalable bioimaging modality; one can choose low acoustic resolution with deep penetration depth or high optical resolution with shallow imaging depth. High spatial resolution and deep penetration depth is rather difficult to achieve using a single system. Here we report a switchable acoustic resolution and optical resolution photoacoustic microscopy (AR-OR-PAM) system in a single imaging system capable of both high resolution and low resolution on the same sample. Lateral resolution of 4.2 µm (with ~1.4 mm imaging depth) and lateral resolution of 45 μm (with ~7.6 mm imaging depth) was successfully demonstrated using a switchable system. In vivo blood vasculature imaging was also performed for its biological application.

Performance Characterization of a Switchable Acoustic Resolution and Optical Resolution Photoacoustic Microscopy System.

Photoinduced shrinkage occurring in photopolymer layers during holographic recording was determined by phase shifting electronic speckle pattern interferometry. Phase maps were calculated from the changes in intensity at each pixel due to the phase differences introduced between object and reference beams. Shrinkage was then obtained from the changes in phase as recording proceeded. The technique allows for whole field measurement of the dimensional changes in photopolymers during holographic recording.

Mohesh Moothanchery

School of Chemical and Biomedical Engineering

Nanyang Technological University

Switchable Acoustic and Optical Resolution Photoacoustic Microscopy for In Vivo Small-animal Blood Vasculature Imaging

Mohesh Moothanchery

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}School of Chemical and Biomedical Engineering

Nanyang Technological University

Switchable Acoustic and Optical Resolution Photoacoustic Microscopy for In Vivo Small-animal Blood Vasculature Imaging

School of Chemical and Biomedical Engineering