In this proceeding we discuss the recent work involving our developed optogenetic tool, where we use digital light processor (DLP) as a light-stimulation source of neuronal culture and microelectrode array (MEA) system as the sampling unit. In this work we aim at developing an integrated experimental platform which should assist in the study of the structure and the function of neuronal networks. In particular, the setup proposed in this work should serve as an optogenetic tool for in-vitro experiments, controlled by a feedback from electrophysiological signals from the network to address specific neuronal circuits. In this manuscript some of the recent results from experiments involving optical stimulation and electrophysiological recording of neuronal cultures are shown. Additionally, we have developed an AI-based model which is trained according the recorded electrophysiological signals and reproduces the functionality and the macro-structure of the culture under test. The description and some preliminary results of this model are also discussed in this proceeding.
To study the brain and the related neuronal network activity, many attempts were made to design and develop platforms able to induce and record neuronal signals. However, many brain processes - like memory formation and storage - and diseases - like amnesia or epilepsy - need more basic studies. For these, a bottom-up approach is needed, starting from 2D in-vitro neuronal cultures. In this work, we will present two experimental systems able to optogenetically interact with 2D neuronal networks with patternized light. One system consists in a Digital Light Projector (DLP) integrated in a microscope setup, which can illuminate neurons from the top; the other, is a compact and transportable photonic chip, properly designed to illuminate neurons plated on its surface.
We report on recent experimental and theoretical studies of cesium laser, where we focused on the beam propagation factor M2 in flowing-gas Cs DPALs with stable optical resonators and of its dependence on the resonator geometry. The measured results were modeled by multi-transverse-mode model [Auslender et al., Opt. Express 25, 19767 (2017)]. Conditions for substantial improvement of the output laser beam quality, reducing M2 to close to unity, are found. In particular we show how changing the length of the resonator, and/or the radius of curvature of the high reflection mirror, leaving all other parameters of the laser unchanged, makes it possible to control the beam quality.
The beam quality and efficiency of diode-pumped alkali lasers are strongly dependent on parameters such as the pump beam geometry, the resonator configuration, the gain length and other features. In the present work we studied experimentally and theoretically the dependence of some of these parameters on the laser performance. An optical model of multi-transverse mode operation of alkali vapor lasers [Auslender et al, Opt. Express 25, 19767 (2017)], modified for the current experiments, is applied to the experimental results. The values of the laser power and M2 predicted by the model are in good agreement with the experimental results for different shapes and powers of the pump beam.
KEYWORDS: Cesium, 3D modeling, Continuous wave operation, Semiconductor lasers, Temperature metrology, Diodes, Gas lasers, Mirrors, Chemical species, Reflectivity
We report on the results of ongoing work in our lab on flowing-gas Cs DPAL. Some of the results have been already reported [Yacoby et al, Opt. Express 26, 17814 (2018)] but we briefly describe them here again to give a full picture of the work. Experimental and theoretical study of continuous wave Cs DPAL with gas circulation (He and CH4), flow velocities of 1-4.5 m/s and pump powers of 30-65 W, is reported. For the theoretical part of the study we used a 3D computational fluid dynamics model, solving the gas dynamics and kinetics equations relevant to flowing-gas laser operation. Maximum CW output power of 24 W and slope efficiency of 48% were obtained. The experimental and theoretical dependence of the lasing power on the flow velocity are in good agreement. The gas temperature rise in the laser cell was measured. The lasing power was not affected by the flow velocity at this range of pump powers and flow velocities due to the fact that the gas temperature rise was only several degrees. It was estimated – using a “fitting” method – that the quenching cross-section of the excited levels of Cs to the ground state is ~ 0.05 Å2 .
Experimental and theoretical parametric study of static and flowing-gas diode-pumped Cs lasers is reported. In the static case dependence of the output laser power and the beam quality factor M2 on the power and spatial shape of the pump beam is studied. An optical model of multi-transverse mode operation of alkali vapor lasers [Auslender et al, Opt. Express 25, 19767 (2017)] is applied to the experimental results. The values of the laser power and M2 predicted by the model are in good agreement with the experimental results for different shapes and powers of the pump beam We also report, briefly, on our recently published work [Yacoby et al, Opt. Express 26, 17814 (2018)] on flowing-gas Cs-DPAL where the output power and gas temperature rise in the laser cell at different flow velocities were studied and the results analyzed by our three-dimensional computational fluid-dynamics) model.
In the present paper we use a simple optical model to describe multi-transverse mode operation of alkali lasers. The model is based on calculations of the pump and laser beam intensities in the gain medium, where the laser beam intensity is a linear combination of the azimuthally-symmetric Laguerre-Gaussian modes. The model was applied to optically pumped cesium vapor laser studied experimentally and theoretically previously [Cohen, T., Lebiush, E., Auslender, I., Barmashenko B.D., and Rosenwaks, S., Opt. Exp. 24, 14374 (2016)]. It was found in our calculations that for low pump power and small pump beam radii, only fundamental lasing mode oscillates, just as shown experimentally in this study. However, for higher pump powers and larger pump beam diameters, several transverse modes participate in oscillation. The number and intensities of the oscillating modes as a function of the pump beam power and radius are found. In order to check the validity of the model, it was applied to pulsed static Cs DPAL [Zhdanov, B. et al, Electron. Lett. 44, 582(2008)] with the pump beam radius much larger than that of the fundamental laser mode and constant gas temperature. The model predicts linear dependence of the laser power on the pump power, the values of the former being in agreement with the experimental results.
The pump-to-laser beam overlap and the cell length of static diode-pumped Cs lasers are crucial parameters for optimization of these lasers. In a previous publication we modeled the influence of the pump-to-laser beam overlap on the performance of Ti:Sapphire pumped cesium vapor laser (T. Cohen, E. Lebiush, I. Auslender, B.D. Barmashenko and S. Rosenwaks, Opt. Exp. 24, 14374 (2016)). In the present paper we report on experiments and modeling in progress on diode pumped cesium vapor laser.
We present the results of an experimental study of Ti:Sapphire pumped Cs laser and theoretical modeling of these results, where we focused on the influence of the pump-to-laser beam overlap, a crucial parameter for optimizing the output laser power. The dependence of the output laser power on the incident pump power was found for varying pump beam cross-section widths and for a constant laser beam. Maximum laser power > 370 mW with an optical-to-optical efficiency of 43% and slope efficiency ~55% was obtained. Non monotonic dependence of the laser power and threshold power on the pump beam radius (at a given pump power) was observed with a maximum laser power and minimum threshold power achieved at the ratio ~0.7 between the optimal pump beam and laser beam radius. A simple optical model of the laser, where Gaussian spatial shapes of the pump and laser intensities in any cross section of the beams were assumed, was compared to the experiments. Good agreement was obtained between the measured and calculated dependence of the laser power on the incident pump power at different pump beam radii and of the laser power, threshold power and optimal temperature on the pump beam radius. The model does not use empirical parameters such as mode overlap efficiency but rather the pump and laser beam spatial shapes as input parameters. This model can be applied to different optically pumped alkali lasers with arbitrary spatial distributions of the pump and laser beam widths.
We report on the results of an experimental study of Ti:Sapphire pumped Cs laser and theoretical modeling of these
results, where we focused on the influence of the pump-to-laser beam overlap, a crucial parameter for optimizing the
output laser power. Non monotonic dependence of the laser power (optimized over the temperature) on the pump beam
radius was observed with a maximum achieved at the ratio ~ 0.7 between the pump and laser beam radii. The optimal
temperature decreased with increasing pump beam radius. Maximum laser power > 370 mW with an optical-to-optical
efficiency of 43% and slope efficiency ~ 55% was obtained. A simple optical model of the laser, where Gaussian spatial
shapes of the pump and laser intensities in any cross section of the beams were assumed, was compared to the
experiments. Good agreement was obtained between the measured and calculated dependence of the laser power on the
pump power at different pump beam radii and also of the laser power, threshold pump power and optimal temperature on
the pump beam radius. The model does not use empirical parameters such as mode overlap efficiency but rather the
pump and laser beam spatial shapes as input parameters. The present results combined with results of the application of
the model to K DPAL and Ti:Sapphire pumped Cs laser, indicate that the model can describe the operation of different
optically pumped alkali lasers with arbitrary spatial distributions of the pump and laser beam widths.
Modeling of static and flowing-gas subsonic, transonic and supersonic Cs and K Ti:Sapphire and diode pumped alkali lasers (DPALs) is reported. A simple optical model applied to the static K and Cs lasers shows good agreement between the calculated and measured dependence of the laser power on the incident pump power. The model reproduces the observed threshold pump power in K DPAL which is much higher than that predicted by standard models of the DPAL. Scaling up flowing-gas DPALs to megawatt class power is studied using accurate three-dimensional computational fluid dynamics model, taking into account the effects of temperature rise and losses of alkali atoms due to ionization. Both the maximum achievable power and laser beam quality are estimated for Cs and K lasers. The performance of subsonic and, in particular, supersonic DPALs is compared with that of transonic, where supersonic nozzle and diffuser are spared and high power mechanical pump (needed for recovery of the gas total pressure which strongly drops in the diffuser), is not required for continuous closed cycle operation. For pumping by beams of the same rectangular cross section, comparison between end-pumping and transverse-pumping shows that the output power is not affected by the pump geometry, however, the intensity of the output laser beam in the case of transverse-pumped DPALs is strongly non-uniform in the laser beam cross section resulting in higher brightness and better beam quality in the far field for the end-pumping geometry where the intensity of the output beam is uniform.
We report on a model of highly efficient static, pulsed K DPAL [Zhdanov et al, Optics Express 22, 17266 (2014)], where
Gaussian spatial shapes of the pump and laser intensities in any cross section of the beams are assumed. The model
shows good agreement between the calculated and measured dependence of the laser power on the incident pump power.
In particular, the model reproduces the observed threshold pump power, 22 W (corresponding to pump intensity of 4
kW/cm2), which is much higher than that predicted by the standard semi-analytical models of the DPAL. The reason for
the large values of the threshold power is that the volume occupied by the excited K atoms contributing to the
spontaneous emission is much larger than the volumes of the pump and laser beams in the laser cell, resulting in very
large energy losses due to the spontaneous emission. To reduce the adverse effect of the high threshold power, high
pump power is needed, and therefore gas flow with high gas velocity to avoid heating the gas has to be applied. Thus, for
obtaining high power, highly efficient K DPAL, subsonic or supersonic flowing-gas device is needed.
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