Signal and response properties indicate an optoacoustic effect underlying the intra-cochlear laser-optical stimulation

Optical cochlea stimulation is under investigation as a potential alternative to conventional electric cochlea implants in treatment of sensorineural hearing loss. If direct optical stimulation of spiral ganglion neurons (SGNs) would be feasible, a smaller stimulation volume and, therefore, an improved frequency resolution could be achieved. However, it is unclear whether the mechanism of optical stimulation is based on direct neuronal stimulation or on optoacoustics. Animal studies on hearing vs. deafened guinea pigs already identified the optoacoustic effect as potential mechanism for intra-cochlear optical stimulation. In order to characterize the optoacoustic stimulus more thoroughly the acoustic signal along the beam path of a pulsed laser in water was quantified and compared to the neuronal response properties of hearing guinea pigs stimulated with the same laser parameters. Two pulsed laser systems were used for analyzing the influence of variable pulse duration, pulse energy, pulse peak power and absorption coefficient. Preliminary results of the experiments in water and in vivo suggesta similar dependency of response signals on the applied laser parameters: Both datasets show an onset and offset signal at the beginning and the end of the laser pulse. Further, the resulting signal amplitude depends on the pulse peak power as well as the temporal development of the applied laser pulse. The data indicates the maximum of the first derivative of power as the decisive factor. In conclusion our findings strengthen the hypothesis of optoacoustics as the underlying mechanism for optical stimulation of the cochlea. © SPIE 201

Scanning laser optical tomography for in toto imaging of the murine cochlea

The mammalian cochlea is a complex macroscopic structure due to its helical shape and the microscopic arrangements of the individual layers of cells. To improve the outcomes of hearing restoration in deaf patients, it is important to understand the anatomic structure and composition of the cochlea ex vivo. Hitherto, only one histological technique based on confocal laser scanning microscopy and optical clearing has been developed for in toto optical imaging of the murine cochlea. However, with a growing size of the specimen, e.g., human cochlea, this technique reaches its limitations. Here, we demonstrate scanning laser optical tomography (SLOT) as a valuable imaging technique to visualize the murine cochlea in toto without any physical slicing. This technique can also be applied in larger specimens up to cm3 such as the human cochlea. Furthermore, immunolabeling allows visualization of inner hair cells (otoferlin) or spiral ganglion cells (neurofilament) within the whole cochlea. After image reconstruction, the 3D dataset was used for digital segmentation of the labeled region. As a result, quantitative analysis of position, length and curvature of the labeled region was possible. This is of high interest in order to understand the interaction of cochlear implants (CI) and cells in more detail. © 2017 Nolte et al.This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.DFG/EXC/1077/1Ministry of Lower SaxonyVolkswagenStiftun

Interaction mechanisms of cavitation bubbles induced by spatially and temporally separated fs-laser pulses.

The emerging use of femtosecond lasers with high repetition rates in the MHz regime together with limited scan speed implies possible mutual optical and dynamical interaction effects of the individual cutting spots. In order to get more insight into the dynamics a time-resolved photographic analysis of the interaction of cavitation bubbles is presented. Particularly, we investigated the influence of fs-laser pulses and their resulting bubble dynamics with various spatial as well as temporal separations. Different time courses of characteristic interaction effects between the cavitation bubbles were observed depending on pulse energy and spatio-temporal pulse separation. These ranged from merely no interaction to the phenomena of strong water jet formation. Afterwards, the mechanisms are discussed regarding their impact on the medical application of effective tissue cutting lateral to the laser beam direction with best possible axial precision: the mechanical forces of photodisruption as well as the occurring water jet should have low axial extend and a preferably lateral priority. Furthermore, the overall efficiency of energy conversion into controlled mechanical impact should be maximized compared to the transmitted pulse energy and unwanted long range mechanical side effects, e.g. shock waves, axial jet components. In conclusion, these experimental results are of great importance for the prospective optimization of the ophthalmic surgical process with high-repetition rate fs-lasers

Modeling of photoluminescence in laser-based lighting systems

The development of laser-based lighting systems has been the latest step towards a revolution in illumination technology brought about by solid-state lighting. Laser-activated remote phosphor systems produce white light sources with significantly higher luminance than LEDs. The weak point of such systems is often considered to be the conversion element. The high-intensity exciting laser beam in combination with the limited thermal conductivity of ceramic phosphor materials leads to thermal quenching, the phenomenon in which the emission efficiency decreases as temperature rises. For this reason, the aim of the presented study is the modeling of remote phosphor systems in order to investigate their thermal limitations and to calculate the parameters for optimizing the efficiency of such systems. The common approach to simulate remote phosphor systems utilizes a combination of different tools such as ray tracing algorithms and wave optics tools for describing the incident and converted light, whereas the modeling of the conversion process itself, i.e. photoluminescence, in most cases is circumvented by using the absorption and emission spectra of the phosphor material. In this study, we describe the processes involved in luminescence quantum-mechanically using the single-configurational-coordinate diagram as well as the Franck-Condon principle and propose a simulation model that incorporates the temperature dependence of these processes. Following an increasing awareness of climate change and environmental issues, the development of ecologically friendly lighting systems featuring low power consumption and high luminous efficiency is imperative more than ever. The better understanding of laser-based lighting systems is an important step towards that aim as they may improve on LEDs in the near future. © 2017 SPIE

Schematic depiction of the adjustment of subsequent generated cavitation bubbles.

<p>The first bubble is induced on the left side at a time defined as t₁ = 0.0 µs. The second cavity is generated at t₂ after a constant delay of 10.0 µs. The bubble size is characterized as its radius R_Cav while the distance between the focal spots amounts to Δr.</p

Overview of the analyzed sample media with adapted spot separation.

<p>Overview of the analyzed sample media and the applied laser parameters pulse energy E_pulse (also in multiple of the threshold E_th for de-ionized water, the given values lie within the precision of the threshold determination) and spot separation Δr. By adapting these for the different media spatial overlap parameters η_r within the same range as for water are achieved. In this case, the observable interaction mechanisms correspond.</p><p>Overview of the analyzed sample media with adapted spot separation.</p

Overview of the analyzed sample media with constant spot separation.

<p>Overview of the analyzed sample media and the applied laser parameters pulse energy E_pulse (also in multiple of the threshold E_th for de-ionized water, the given values lie within the precision of the threshold determination) and spot separation Δr, which are constant here for all media. However, the resulting spatial overlap parameter η_r as well as the observable interaction mechanism vary for different mechanical properties.</p><p>Overview of the analyzed sample media with constant spot separation.</p

Cavitation bubble dynamics of different observable interaction mechanisms.

<p>The first cavitation bubble occurs at about 0.0 µs for every image series. Its single bubble dynamics is shown in two more frames at 5.0 µs and 9.0 µs. The second cavity with defined temporal and spatial separation appears at 10.0 µs next to the first one. Afterwards the dynamics of the cavitation bubble interaction is shown at selected points in time. A more detailed depiction with equidistant time steps can be seen in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114437#pone.0114437.s002" target="_blank">S2 Figure</a>. Especially, the jet formation of interaction mechanism 7 is shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114437#pone-0114437-g004" target="_blank">Fig. 4</a> for the whole duration of oscillation and for the total jet length.</p

Contour depiction of the jet characteristics scaled with the applied laser pulse energy.

<p>Jet length within the parameter space of (<b>a</b>) focus separation and pulse energy (scaling the temporal overlap) as well as (<b>b</b>) spatial overlap parameter η_r and temporal overlap parameter η_t, and jet velocity as a function of (<b>c</b>) focus separation and pulse energy as well as (<b>d</b>) the overlap parameters η_r and η_t. The cross signs the maximum impact on the untreated medium (here water) at a maximum value for jet length and velocity at the same time. The dashed and dotted lines show supposed borders between the previously introduced interaction scenarios for visual assistance.</p

Detailed bubble dynamics of two cavities in the observable interaction mechanism 7.

<p>The parameters to observe mechanism 7 were here a focus separation of Δr = 71.8 µm and a laser pulse energy of E_pulse = 10.7-times E_th. The image series begins with the occurrence of the second cavity at 10 µs. Afterwards, the dominating jet formation in laser scanning direction is shown with the overall jet length by composing two images covering different imaging regions within the cuvette at the same time delay. A more detailed time evolution of the effects and the whole dynamics in equidistant time steps is shown in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114437#pone.0114437.s003" target="_blank">S3 Figure</a>).</p