Category: Interferometric detectors

source: © 2018 Light: Science & Applications

Originally developed for diagnostic ultrasound imaging, piezoelectric transducers are the most widespread technology employed in optoacoustic (photoacoustic) signal detection. However, the detection requirements of optoacoustic sensing and imaging differ from those of conventional ultrasonography and lead to specifications not sufficiently addressed by piezoelectric detectors. Consequently, interest has shifted to utilizing entirely optical methods for measuring optoacoustic waves. All-optical sound detectors yield a higher signal-to-noise ratio per unit area than piezoelectric detectors and feature wide detection bandwidths that may be more appropriate for optoacoustic applications, enabling several biomedical or industrial applications. Additionally, optical sensing of sound is less sensitive to electromagnetic noise, making it appropriate for a greater spectrum of environments. In this review, we categorize different methods of optical ultrasound detection and discuss key technology trends geared towards the development of all-optical optoacoustic systems. We also review application areas that are enabled by all-optical sound detectors, including interventional imaging, non-contact measurements, magnetoacoustics, and non-destructive testing.[Read More…]

Fig. 1 a Intensity-sensitive detection of refractive index. b Single-beam deflectometry. c Phase-sensitive ultrasound detection with a Schlieren beam. d Phase-sensitive ultrasound detection with a decoupled optoacoustic source. AL acoustic lens, CMOS CMOS camera, FP Fourier plane, L lens, LA laser, P prism, PD photodiode, QPD quadrant photodiode, SB Schlieren beam, SF spatial filter, US ultrasound

Georg Wissmeyer, Miguel A. Pleitez, Amir Rosenthal & Vasilis Ntziachristos ,”Looking at sound: optoacoustics with all-optical ultrasound detection”, in Light: Science & Applications volume 7, Article number: 53 (2018)

source: © 2018 Optical Society of America

In the optical detection of ultrasound, resonators with high Q-factors are often used to maximize sensitivity. However, increasing the Q-factor of a resonator may reduce the linear range of the interrogation scheme, making it more susceptible to strong external perturbations and incapable of measuring strong acoustic signals. In this Letter, a passive-demodulation scheme for pulse interferometry was developed for high dynamic-range measurements. The passive scheme was based on an unbalanced Mach–Zehnder interferometer and a 90° optical hybrid, which was implemented in a dual-polarization all-fiber setup. We demonstrated the passive scheme for detecting ultrasound bursts with pressure levels for which the response of conventional, active interferometric techniques became nonlinear. [Read More…]

Fig. 1. (a) Schematic drawing of the system used for pulse interferometry. (b) Active-demodulation scheme consists of an unbalanced Mach–Zehnder interferometer (MZI) stabilized to quadrature using a wideband feedback circuit. PZ is piezoelectric fiber stretcher, and FC is 50/50 fused fiber coupler. (c) Passive-demodulation scheme consists of a dual-polarization unbalanced MZI, implementing a 90° optical hybrid. PBS is polarization beam splitter.

Yoav Hazan and Amir Rosenthal, “Passive-demodulation pulse interferometry for ultrasound detection with a high dynamic range,” Opt. Lett. 43, 1039-1042 (2018)

source: © 2017 Optical Society of America

With recent advances in optical technology, interferometric sensing has grown into a highly versatile approach for ultrasound detection, with many interferometric detectors relying on optical waveguides to achieve high levels of sensitivity and miniaturization. In this Letter, we establish a practical model for assessing the sensitivity of silicon-photonics waveguides to acoustic waves. The analysis is performed for different polarizations, waveguide dimensions, and acoustic wave types. Our model was validated experimentally in the acoustic frequency band of 1–13 MHz by measuring the sensitivities of the two polarization modes in a silicon strip waveguide. Both the experimental results and theoretical prediction show that the transverse-magnetic polarization achieves a higher sensitivity and suppression of surface acoustic waves compared to the transverse-electric polarization for the geometries studied. [Read More…]

Fig. 2. Numerical calculation of normalized sensitivity ?? as a function of the waveguide width (??) and height (??) and polarization for (a), (b) the longitudinal acoustic wave in normal incidence and (c), (d) SAWs created in oblique incidence.

Shai Tsesses, Daniel Aronovich, Assaf Grinberg, Evgeny Hahamovich, and Amir Rosenthal “Modeling the sensitivity dependence of silicon-photonics-based ultrasound detectors”, Optics Letters Vol. 42, Issue 24, pp. 5262-5265 (2017)

source: © 2017 Optical Society of America

The addition of optoacoustic sensing to optical microscopy may supplement fluorescence contrast with label-free measurements of optical absorption, enhancing biological observation. However, the physical dimensions of many optoacoustic systems have restricted the implementation of hybrid optical and optoacoustic (O2A) microscopy to imaging thin samples in transmission mode or to ex-vivo investigations. Here we describe a miniaturized optoacoustic sensor, based on a ?-phase-shifted fiber Bragg grating embedded in an acoustic cavity, which is virtually invisible to the optical path and can be seamlessly integrated into any conventional optical microscope. The new sensor enables, for the first time to our knowledge, entirely optical O2A intravital microscopy in epi-illumination mode, demonstrated by label-free optoacoustic and second-harmonic generation images of a mouse abdomen and ear. Our technique greatly simplifies the integration of acoustic detection in standard microscopes and could therefore make optoacoustic microscopy more accessible to the biomedical community. [Read More…]

Fig. 5. Schematic depiction of the O2A microscopy setup: A standard inverted microscope with laser sources for optoacoustic and non-linear optical imaging is combined with galvanometric mirrors for fast laser raster scanning. The sensor is mounted on the microscope objective, with a tunable CW laser coupled to the embedded ?-FBG. The inset shows the 3D printed platform supporting an anesthetized mouse and mounted on a ??? positioning stage. DM, dichroic mirror; BP, bandpass filter; PH, pinhole; ND, neutral density filter; BS, beam splitter; PMT, photomultiplier tube; OA, optoacoustic; DAQ, data acquisition card.

Authors: Rami Shnaiderman, Georg Wissmeyer, Markus Seeger, Dominik Soliman, Hector Estrada, Daniel Razansky, Amir Rosenthal, and Vasilis Ntziachristos, “Fiber interferometer for hybrid optical and optoacoustic intravital microscopy,” Optica 4, 1180-1187 (2017)

source:© 2016 Optical Society of America

Optical and optoacoustic (photoacoustic) microscopy have been recently joined in hybrid implementations that resolve extended tissue contrast compared to each modality alone. Nevertheless, the application of the hybrid technique is limited by the requirement to combine an optical objective with ultrasound detection collecting signal from the same micro-volume. We present an all-optical optoacoustic microscope based on a pi-phase-shifted fiber Bragg grating (?-FBG) with coherence-restored pulsed interferometry (CRPI) used as the interrogation method. The sensor offers an ultra-small footprint and achieved higher sensitivity over piezoelectric transducers of similar size. We characterize the spectral bandwidth of the ultrasound detector and interrogate the imaging performance on phantoms and tissues. We show the first optoacoustic images of biological specimen recorded with ?-FBG sensors. We discuss the potential uses of ?-FBG sensors based on CRPI.
[Read More…]

Fig. 1. Schematic of the all-optical optoacoustic microscope. ND, neutral density filter; L, lens; M, mirror; PH, pinhole; xyz, motorized translation stages; DAQ, data acquisition system; EDFA, erbium-doped optical amplifier; PZ, piezoelectric fiber stretcher.

G. Wissmeyer, D. Soliman, R. Shnaiderman, A. Rosenthal, and V. Ntziachristos, “All-optical optoacoustic microscope based on wideband pulse interferometry,” Opt. Lett. Vol. 41, pp. 1953-1956 (2016).

source: © 2016 Physical Review Letters

The interaction of magnetic nanoparticles and electromagnetic fields can be determined through electrical signal induction in coils due to magnetization. However, the direct measurement of instant electromagnetic energy absorption by magnetic nanoparticles, as it relates to particle characterization or magnetic hyperthermia studies, has not been possible so far. We introduce the theory of magnetoacoustics, predicting the existence of second harmonic pressure waves from magnetic nanoparticles due to energy absorption from continuously modulated alternating magnetic fields. We then describe the first magnetoacoustic system reported, based on a fiber-interferometer pressure detector, necessary for avoiding electric interference. The magnetoacoustic system confirmed the existence of previously unobserved second harmonic magnetoacoustic responses from solids, magnetic nanoparticles, and nanoparticle-loaded cells, exposed to continuous wave magnetic fields at different frequencies. We discuss how magnetoacoustic signals can be employed as a nanoparticle or magnetic field sensor for biomedical and environmental applications.
[Read More…]

Figure 1
Concept of magnetoacoustic signal induction. (a) Components of the magnetoacoustic setup. Power supply (PS), modulator (M), water chiller (W), driver (D). (b) Magnetoacoustic sensing using a PZT transducer. The sample comprises a steel rod located within the coil. (c) rf-free magnetoacoustic sensing employing a fiber-Bragg-based interferometric ultrasound sensor in a horizontally arranged solenoid (water tank not displayed). The optical sensor comprises optical filters (F), an erbium-doped fiber amplifier (EFDA), a 99/1optical splitter (S), a demodulator (Demod), and the π-shifted FBG sensing unit. (d) Magnetoacoustic sensing of a steel rod specimen using PZT based ultrasound detection. rf interference due to the nonlinearity of the rf amplifier (blue dotted line) and experimental confirmation of the second harmonic magnetoacoustic signal (red line) induced in conducting material at f_MA=2f_rf. Inset shows the quadratic increase of detected magnetoacoustic signal (red crosses) as a function of the linearly rising B field compared to the expected theory (dashed black curve) and a linear relationship (dotted green line).

Kellnberger, A. Rosenthal, A. Myklatun, G. G. Westmeyer, G. Sergiadis, and V. Ntziachristos, ” Magnetoacoustic sensing of magnetic nanoparticles,” Phys. Rev. Lett., Vol. 116, 108103 (2016).