scholarly journals Interferometric imaging of thermal expansion for temperature control in retinal laser therapy

2021 ◽  
Author(s):  
David Veysset ◽  
Tong Ling ◽  
Yueming Zhuo ◽  
Daniel Palanker
Keyword(s):  
Thermal Expansion ◽  
Laser Therapy ◽  
Temperature Rise ◽  
Path Length ◽  
Optical Path Length ◽  
Optical Path ◽  
Laser Exposure ◽  
Interferometric Imaging ◽  
Tissue Phantom ◽  
Length Changes

Precise control of the temperature rise is a prerequisite for proper photothermal therapy. In retinal laser therapy, the heat deposition is primarily governed by the melanin concentration, which can significantly vary across the retina and from patient to patient. In this work, we present a method for determining the optical and thermal properties of layered materials, directly applicable to the retina, using low-energy laser heating and phase-resolved optical coherence tomography (pOCT). The method is demonstrated on a polymer-based tissue phantom heated with a laser pulse focused onto an absorbing layer buried below the phantom's surface. Using a line-scan spectral-domain pOCT, optical path length changes induced by the thermal expansion were extracted from sequential B-scans. The material properties were then determined by matching the optical path length changes to a thermo-mechanical model developed for fast computation. This method determined the absorption coefficient with a precision of 2.5% and the temperature rise with a precision of about 0.2°C from a single laser exposure, while the peak did not exceed 8°C during 1 ms pulse, which is well within the tissue safety range and significantly more precise than other methods.

Determination of Refractive Indices and Linear Coefficients of Thermal Expansion for Development of Athermal Glass

2011 ◽  
Vol 675-677 ◽  
pp. 1113-1116
Author(s):  
Yoshinao Kobayashi ◽  
Taiichi Shimizu ◽  
Rie Endo ◽  
Masahiro Susa
Keyword(s):  
Refractive Index ◽  
Thermal Expansion ◽  
Temperature Dependence ◽  
Path Length ◽  
Sessile Drop ◽  
Coefficient Of Thermal Expansion ◽  
Optical Path Length ◽  
Optical Path ◽  
Linear Coefficient ◽  
Optical Fibre Transmission

Recently, there has been a growing importance of development of ‘athermal glass’ having no temperature dependence in its optical path length and is expected to be used in optical devices for the optical fibre transmission system. The athermal characteristic is usually evaluated by temperature dependence of optical path length, (1/l)･(dS/dT) ( l : geometrical length, S : optical path length, T : temperature), which is the summation of nα and dn/dT (n: refractive index, α: linear coefficient of thermal expansion). In the present work, the refractive index and liner coefficient of thermal expansion have been determined for silicate glasses containing titanium oxides in the temperature range from room temperature to about 673 K, using ellipsometry and utilizing the sessile drop method. The values of nα and temperature coefficient of n ranged from 1.289×10-5 K-1 to 3.345×10-5 K-1 and from 0.270×10-5 K-1 to 1.467×10-5 K-1, respectively, depending on the glass composition. Consequently, only 80SiO2-5TiO2-15Na2O glass has shown almost the same degree of athermal characteristic as SiO2 glass, having more advantages in practice due to its lower melting temperature than SiO2.

scholarly journals In vivo optical imaging of physiological responses to photostimulation in human photoreceptors

2016 ◽  
Vol 113 (46) ◽  
pp. 13138-13143 ◽  
Author(s):  
Dierck Hillmann ◽  
Hendrik Spahr ◽  
Clara Pfäffle ◽  
Helge Sudkamp ◽  
Gesa Franke ◽  
...  
Keyword(s):  
Path Length ◽  
Ex Vivo ◽  
Optical Path Length ◽  
Optical Path ◽  
Clinical Diagnostics ◽  
Photoreceptor Outer Segment ◽  
Cellular Processes ◽  
Tomography System ◽  
Length Changes

Noninvasive functional imaging of molecular and cellular processes of vision may have immense impact on research and clinical diagnostics. Although suitable intrinsic optical signals (IOSs) have been observed ex vivo and in immobilized animals in vivo, detecting IOSs of photoreceptor activity in living humans was cumbersome and time consuming. Here, we observed clear spatially and temporally resolved changes in the optical path length of the photoreceptor outer segment as a response to an optical stimulus in the living human eye. To witness these changes, we evaluated phase data obtained with a parallelized and computationally aberration-corrected optical coherence tomography system. The noninvasive detection of optical path length changes shows neuronal photoreceptor activity of single cones in living human retina, and therefore, it may provide diagnostic options in ophthalmology and neurology and could provide insights into visual phototransduction in humans.

scholarly journals Correction for stress-induced optical path length changes in a refractometer cell at variable external pressure

Metrologia ◽  
2018 ◽  
Vol 56 (1) ◽  
pp. 015001 ◽  
Author(s):  
Guido Bartl ◽  
Stephanie Glaw ◽  
Frank Schmaljohann ◽  
René Schödel
Keyword(s):  
Path Length ◽  
Optical Path Length ◽  
External Pressure ◽  
Optical Path ◽  
Length Changes

Nanometer-scale displacement sensing using self-mixing interferometry with a correlation-based signal processing technique

2006 ◽  
Vol 14 (2) ◽  
Author(s):  
J. Hast ◽  
M. Okkonen ◽  
H. Heikkinen ◽  
L. Krehut ◽  
R. Myllylä
Keyword(s):  
Signal Processing ◽  
Phase Difference ◽  
Laser Diode ◽  
Path Length ◽  
Spline Interpolation ◽  
External Cavity ◽  
Optical Path Length ◽  
Optical Path ◽  
Interference Signal ◽  
Length Changes

AbstractA self-mixing interferometer is proposed to measure nanometre-scale optical path length changes in the interferometer’s external cavity. As light source, the developed technique uses a blue emitting GaN laser diode. An external reflector, a silicon mirror, driven by a piezo nanopositioner is used to produce an interference signal which is detected with the monitor photodiode of the laser diode. Changing the optical path length of the external cavity introduces a phase difference to the interference signal. This phase difference is detected using a signal processing algorithm based on Pearson’s correlation coefficient and cubic spline interpolation techniques. The results show that the average deviation between the measured and actual displacements of the silicon mirror is 3.1 nm in the 0–110 nm displacement range. Moreover, the measured displacements follow linearly the actual displacement of the silicon mirror. Finally, the paper considers the effects produced by the temperature and current stability of the laser diode as well as dispersion effects in the external cavity of the interferometer. These reduce the sensor’s measurement accuracy especially in long-term measurements.

Investigation of particulate systems using optical pathlength spectroscopy

2000 ◽  
Vol 627 ◽  
Author(s):  
Gabriel Popescu ◽  
Aristide Dogariu
Keyword(s):  
Path Length ◽  
Random Media ◽  
Michelson Interferometer ◽  
Industrial Process ◽  
Optical Path Length ◽  
Industrial Applications ◽  
Optical Path ◽  
Interference Signal ◽  
Optical Length ◽  
Reference Mirror

ABSTRACTIn many industrial applications involving granular media, knowledge about the structural transformations suffered during the industrial process is desirable. Optical techniques are noninvasive, fast, and versatile tools for monitoring such transformations. We have recently introduced optical path-length spectroscopy as a new technique for random media investigation. The principle of the method is to use a partially coherent source in a Michelson interferometer, where the fields from a reference mirror and the sample are combined to obtain an interference signal. When the system under investigation is a multiple-scattering medium, by tuning the optical length of the reference arm, the optical path-length probability density of light backscattered from the sample is obtained. This distribution carries information about the structural details of the medium. In the present paper, we apply the technique of optical path-length spectroscopy to investigate inhomogeneous distributions of particulate dielectrics such as ceramics and powders. The experiments are performed on suspensions of systems with different solid loads, as well as on powders and suspensions of particles with different sizes. We show that the methodology is highly sensitive to changes in volume concentration and particle size and, therefore, it can be successfully used for real-time monitoring. In addition, the technique is fiber optic-based and has all the advantages associated with the inherent versatility.

scholarly journals Stray light characterization with ultrafast time-of-flight imaging

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
L. Clermont ◽  
W. Uhring ◽  
M. Georges
Keyword(s):  
Path Length ◽  
Imaging System ◽  
Time Of Flight ◽  
Optical Path Length ◽  
Optical Path ◽  
Stray Light ◽  
Laser Source ◽  
Space Telescopes ◽  
Characterization Methods ◽  
Instance Space

AbstractUnderstanding stray light (SL) is a crucial aspect in the development of high-end optical instruments, for instance space telescopes. As it drives image quality, SL must be controlled by design and characterized experimentally. However, conventional SL characterization methods are limited as they do not provide information on its origins. The problem is complex due to the diversity of light interaction processes with surfaces, creating various SL contributors. Therefore, when SL level is higher than expected, it can be difficult to determine how to improve the system. We demonstrate a new approach, ultrafast time-of-flight SL characterization, where a pulsed laser source and a streak camera are used to record individually SL contributors which travel with a specific optical path length. Furthermore, the optical path length offers a means of identification to determine its origin. We demonstrate this method in an imaging system, measuring and identifying individual ghosts and scattering components. We then show how it can be used to reverse-engineer the instrument SL origins.

Sign in / Sign up

Export Citation Format

Share Document