Photoacoustic evaluation of surfaces via pulsed evanescent field interaction

Goldschmidt, Benjamin

doi:10.32469/10355/44173

Cited by 4 publications

(11 citation statements)

References 116 publications

(183 reference statements)

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“…21 In this form, ( 0 ) represents the permittivity of free space, (c 0 ) is the speed of light in a vacuum, (ω) is the phase of the light, (x) is the horizontal position along the waveguide, and (λ 0 ) is the wavelength of the light in a vacuum. For a sufficiently thick cladding layer, these equations hold true and describe the intensity of the field within the cladding medium.…”

Section: Frustrated Total Internal Reflectionmentioning

confidence: 99%

“…21 At the surface of an ultrasonic detector, where x = 0, the equation describes the recorded amplitude of the pressure wave as a function of time. As the wave approaches the detector surface, the pressure exponentially increases in amplitude followed by an immediate drop when the wave hits the detector.…”

Section: Photoacousticsmentioning

confidence: 99%

“…Utilized in a wide variety of applications ranging from the detection of circulating tumor cells and malarial indicators to the evaluation and optical characterization of surfaces and thin films, photoacoustics refers to the phenomenon wherein a laser beam of sufficiently short pulse duration is absorbed by a chromophore within a medium, causing the absorber to undergo a rapid thermoelastic expansion, which results in an ultrasonic pressure wave that propagates throughout the medium. 21,[29][30][31][32] This pressure wave can be described mathematically by equation (6):…”

Section: Photoacousticsmentioning

confidence: 99%

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Controlled laser delivery into biological tissue via thin-film optical tunneling and refraction

et al. 2015

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Due to the often extreme energies employed, contemporary methods of laser delivery utilized in clinical dermatology allow for a dangerous amount of high-intensity laser light to reflect off a multitude of surfaces, including the patient's own skin. Such techniques consistently represent a clear and present threat to both patients and practitioners alike. The intention of this work was therefore to develop a technique that mitigates this problem by coupling the light directly into the tissue via physical contact with an optical waveguide. In this manner, planar waveguides cladded in silver with thin-film active areas were used to illuminate agar tissue phantoms with nanosecond-pulsed laser light at 532nm. The light then either refracted or optically tunneled through the active area, photoacoustically generating ultrasonic waves within the phantom, whose peak-to-peak intensity directly correlated to the internal reflection angle of the beam. Consequently, angular spectra for energy delivery were recorded for sub-wavelength silver and titanium films of variable thickness. Optimal energy delivery was achieved for internal reflection angles ranging from 43 to 50 degrees, depending on the active area and thin film geometries, with titanium films consistently delivering more energy across the entire angular spectrum due to their relatively high refractive index. The technique demonstrated herein therefore not only represents a viable method of energy delivery for biological tissue while minimizing the possibility for stray light, but also demonstrates the possibility for utilizing thin films of high refractive index metals to redirect light out of an optical waveguide.

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Section: Frustrated Total Internal Reflectionmentioning

confidence: 99%

Section: Photoacousticsmentioning

confidence: 99%

Section: Photoacousticsmentioning

confidence: 99%

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Controlled laser delivery into biological tissue via thin-film optical tunneling and refraction

et al. 2015

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“…Many sources find it convenient to represent the Evanescent field in terms of irradiance, rather than Electric field intensity [91,144]. The relationship between Irradiance and the Electric field is derived from the Poynting vector, as shown below.…”

Section: Evanescent Fieldsmentioning

confidence: 99%

“…Consequently, the field extends into a third medium, where a percentage of the light is able to escape TIR and revert into a propagating photon within the third medium, as shown in Figure 3.9. This technique has been utilized in a variety of applications including prism couplers, optical filters and switches, biosensors, and in optically characterizing thin films [144,[146][147][148][149][150][151]. Moreover, it is also the basis upon which Photon Tunneling Microscopy functions [152].…”

Section: Frustrated Total Internal Reflectionmentioning

confidence: 99%

Paraxial application of auxiliary devices with waveguide mediated laser irradiation for applications in medical biophotonics

Whiteside¹

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Laser-based medical applications offer minimally-invasive alternatives to traditional procedures; however, the simplistic method of open-air laser transmission poses ocular hazards and negative side effects, along with a fundamentally limited efficacy for patients of darker complexion due to strong optical absorption in the epidermis. Additionally, the traditional irradiation method also inhibits the incorporation of additional technologies that might otherwise enhance therapeutic effects or provide diagnostic benefits, as doing so would otherwise occlude the laser beam path. The research presented herein addresses each of these considerations individually, first by transmitting laser light into tissue through direct contact with a selective-release waveguide, and thereafter incorporating auxiliary equipment on its rear face. Metal clad planar optical waveguides are demonstrated for the transmission of laser light into samples of porcine skin through direct transmission, governed by scaling evanescent leaking through a designated active area by controlling thin film thickness. In one manifestation, an ultrasonic pulser was incorporated to modulate tissue optical properties and thereby improve transmission of light through epidermal and dermal tissues by increasing forward anisotropy; whereas in another, a high frequency ultrasonic transducer was incorporated to detect photoacoustically generated pressure waves to determine depth profiles of chromophores in skin as a foundation for clinical backward-mode photoacoustic tomography.

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Characterization of MgF2 thin films using optical tunneling photoacoustic spectroscopy

Goldschmidt¹,

Rudy²,

Nowak³

et al. 2015

Optics & Laser Technology

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Photoacoustic evaluation of surfaces via pulsed evanescent field interaction

Cited by 4 publications

References 116 publications

Controlled laser delivery into biological tissue via thin-film optical tunneling and refraction

Controlled laser delivery into biological tissue via thin-film optical tunneling and refraction

Paraxial application of auxiliary devices with waveguide mediated laser irradiation for applications in medical biophotonics

Characterization of MgF2 thin films using optical tunneling photoacoustic spectroscopy

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