Glancing angle deposited nanostructured film Fabry-Perot etalons for optical detection of ultrasound

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Journal titleOptics Express
Pages63916400; # of pages: 10
SubjectHigh refractive index; Nanostructured thin film; Optical detection of ultrasound; Photo-acoustic imaging; Photoacoustic signals; Titanium dioxides (TiO2); Transparent semiconductor; Ultrasound transducers; Acoustic impedance; Deposits; Fabrication; Reflection; Refractive index; Sensors; Ultrasonic propagation; Ultrasonic scattering; Ultrasonic testing; Ultrasonic transducers; Ultrasonics; Vapors; Fabry-Perot interferometers
AbstractIn this paper a new class of optical Fabry-Perot-based ultrasound detectors using low acoustic impedance glancing angle deposited (GLAD) films is demonstrated. GLAD is a single-step physical vapor-deposition (PVD) technique used to fabricate porous nanostructured thin films. Using titanium dioxide (TiO2), a transparent semiconductor with a high refractive index (n = 2.4), the GLAD technique can be employed to fabricate samples with tailored nano-porosity, refractive index periodicities, and high Q-factor reflectance spectra. The average acoustic impedance of the porous films is lower than bulk materials which will improve acoustic coupling, especially for high acoustic frequencies. For this work, two filters with high reflection in the C-band range and high transparency in the visible range (∼80%) using GLAD films were fabricated. A 23 μm Parylene C layer was sandwiched between these two GLAD films in order to form a GLAD Fabry Perot Interferometer (GLAD-FPI). A high speed tunable continuous wavelength C-band laser was focused at the FPI and the reflection was measured using a high speed photodiode. The ultrasound pressure modulated the optical thickness of the FPI and hence its reflectivity. The fabricated sensor was tested using a 10 MHz unfocused transducer. The ultrasound transducer was calibrated using a hydrophone. The minimum detectable acoustic pressure was measured as 80 ± 20 Pa and the -3dB bandwidth was measured to be 18 MHz. This ultra-sensitive sensor can be an alternative to piezoelectric ultrasound transducers for any techniques in which ultrasound waves need to be detected including ultrasonic and photoacoustic imaging modalities. We demonstrate our GLAD-FPI for photoacoustic signal detection in optical-resolution photoacoustic microscopy (OR-PAM). To the best of our knowledge, this is the first time that a FPI fabricated using the GLAD method has been used for ultrasensitive ultrasound detection. © 2013 Optical Society of America.
Publication date
AffiliationNational Research Council Canada (NRC-CNRC); Security and Disruptive Technologies
Peer reviewedYes
NPARC number21271847
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Record identifier0509825e-c87e-4005-86ea-9e86a764f8f1
Record created2014-04-23
Record modified2016-05-09
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