Freespace 13
#Freespace 13 free#
5 Experimentally, significant improvements of sensitivity by mode-filtering were shown with the use of a single-mode fiber-coupled detector (FCD). This effect can be explained using different frameworks, either as rejecting more divergent components of the beam which carry lower contrast interference fringes 4 or removing higher-order spatial modes of the beam which carry spectrally shifted interference fringes which lower the contrast (and hence sensitivity) of the ITF. 8 An alternative method of aberration correction is based on spatial-mode-filtering 4, 5, 9 where a single-mode fiber 5, 9 or an optical pinhole 4 is used to reject part of the interrogation light to improve the measurement sensitivity. 4 It was previously shown that both beam and cavity aberrations, 5 surface roughness 6 as well as mirror non-parallelism 4, 7 can lead to severe deterioration of the optical sensitivity of the FPI and that this loss can be partially recovered by the use of aberration correction techniques including adaptive optics. Among different types of optical sensors, FP cavities are especially sensitive to aberrations as their sensing principle is dependent on the high spatial uniformity of the light beam to facilitate efficient interference. 2, 3Īs optical devices, FPIs are sensitive to light beam aberrations, which can have detrimental effects on their performance under certain conditions. In practice, this approach has allowed acoustic sensing in the range of 100 to 10 6 Pa with a very broadband frequency response (bandwidth ∼ 0.1 to 40 MHz). The sensor is then interrogated by tuning the laser wavelength to the point of maximum slope on the ITF (so-called bias wavelength) which translates the acoustic (pressure) waves into a modulation of an optical (interference) signal. This optical resonator has then the ability to elastically deform under pressure, modulating the FP interferometer’s transfer function (ITF), which is a function of the cavity thickness. For this application, a pressure-sensitive FP device is formed by sandwiching a thin layer (10 to 100 μ m) of elastomer (e.g., Parylene C) between two dichroic mirrors. Among them, Fabry–Pérot interferometer (FPI) sensors are particularly promising, as they combine the ability to measure acoustic waves with high spatial resolution and pressure sensitivity. 1 Multiple optical detector types and geometries are constantly being developed and improved with the overarching aim of matching the detection sensitivity of piezoelectric systems. Results: We found that fiber-coupled detectors are superior in terms of both signal level and image quality in realistic all-optical PA tomography settings.Ĭonclusions: Our study has important practical implications in the field of PA imaging, as for most applications and implementations fiber-coupled detectors are relatively easy to employ since they do not require modifications to the core of the system but only to the peripherally located detector.Īll-optical photoacoustic (PA) tomography is an emerging alternative to classical piezoelectric approaches.
#Freespace 13 free#
While spatial mode-filtering has been proposed to alleviate these problems in Fabry–Pérot-based pressure sensors, their real functional advantage has never been properly investigated.Īim: We rigorously and quantitatively compare the performance of free-space and fiber-coupled detectors for Fabry–Pérot-based pressure sensors.Īpproach: We develop and characterize a quantitative correlative setup capable of simultaneous PA imaging using a free space and a fiber-coupled detector. However, free-space optical detectors are prone to optical aberrations, which can degrade the pressure sensitivity and result in deteriorated image quality. Significance: Highly sensitive detection is crucial for all-optical photoacoustic (PA) imaging.
