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Current Opinion in Neurobiology Feb 2012Optogenetics has been revolutionizing circuit neuroscience in the last few years. Optical methods combined with genetics and molecular techniques have provided new tools... (Review)
Review
Optogenetics has been revolutionizing circuit neuroscience in the last few years. Optical methods combined with genetics and molecular techniques have provided new tools for stimulation of neurons, which hold great promise to provide a solution to the circuit mapping problem and more generally provide us with the ability to artificially control the natural stimulus space. Nevertheless, until very recently almost all applications of optogenetics have been based on relatively simple optical schemes mainly used for inducing population activity in neuronal assembles. In this context, alternative optical schemes that enhance the spatial or temporal resolution of excitation and allow for flexible and arbitrary generation of light patterns have all synergetic impact on the development of new optogenetic actuators. In the following we discuss and compare the main new optical techniques that have become available in the recent years. Their respective strengths and limitations as well as their application to different biological contexts are illustrated.
Topics: Animals; Brain; Genetic Techniques; Humans; Molecular Biology; Neural Pathways; Optics and Photonics; Photons
PubMed: 22209216
DOI: 10.1016/j.conb.2011.11.011 -
Science Advances Sep 2016Photons carry linear momentum and spin angular momentum when circularly or elliptically polarized. During light-matter interaction, transfer of linear momentum leads to...
Photons carry linear momentum and spin angular momentum when circularly or elliptically polarized. During light-matter interaction, transfer of linear momentum leads to optical forces, whereas transfer of angular momentum induces optical torque. Optical forces including radiation pressure and gradient forces have long been used in optical tweezers and laser cooling. In nanophotonic devices, optical forces can be significantly enhanced, leading to unprecedented optomechanical effects in both classical and quantum regimes. In contrast, to date, the angular momentum of light and the optical torque effect have only been used in optical tweezers but remain unexplored in integrated photonics. We demonstrate the measurement of the spin angular momentum of photons propagating in a birefringent waveguide and the use of optical torque to actuate rotational motion of an optomechanical device. We show that the sign and magnitude of the optical torque are determined by the photon polarization states that are synthesized on the chip. Our study reveals the mechanical effect of photon's polarization degree of freedom and demonstrates its control in integrated photonic devices. Exploiting optical torque and optomechanical interaction with photon angular momentum can lead to torsional cavity optomechanics and optomechanical photon spin-orbit coupling, as well as applications such as optomechanical gyroscopes and torsional magnetometry.
Topics: Computer Simulation; Lasers; Optical Devices; Optical Tweezers; Optics and Photonics; Photons; Refractometry; Scattering, Radiation; Torque
PubMed: 27626072
DOI: 10.1126/sciadv.1600485 -
Scientific Reports Aug 2022Herein, we theoretically suggest one-dimensional photonic crystal composed of polymer doped with quantum dots and porous silicon. The present simulated design is...
Herein, we theoretically suggest one-dimensional photonic crystal composed of polymer doped with quantum dots and porous silicon. The present simulated design is proposed as a refractive index biosensor structure based on parity-time symmetry. Under the parity-time conditions, the transmittance of the resonant peaks is magnified to be 57,843% for refractive index 1.350, 2725% for 1.390, 2117% for 1.392, 1502% for 1.395, 1011% for 1.399, and 847% for 1.401. By magnification, we can distinguish between different refractive indices. The present design can record an efficiency twice the published designs as clear in the comparison table. Results clear that the sensitivities are 635 nm/RIU and 1,000,000%/RIU. So, it can be used for a broader range of detection purposes.
Topics: Biosensing Techniques; Optics and Photonics; Photons; Refractometry; Silicon
PubMed: 35961999
DOI: 10.1038/s41598-022-17676-0 -
Journal of the Optical Society of... Jul 2002The photon path distribution (PPD) is a measure that I have developed to express optical responses in inhomogeneous turbid media in the time and frequency domains. The...
The photon path distribution (PPD) is a measure that I have developed to express optical responses in inhomogeneous turbid media in the time and frequency domains. The PPD is defined by local photon pathlengths of possible photons having total zigzag pathlengths I between the points of light input and detection. Such a distribution is independent of absorption and is uniquely determined for the medium under quantification. I show that the PPD is derived through the local photon count of the possible photons arising from an optical impulse incident on an imaginary medium having the same optical properties as the medium under quantification, except for the absence of absorption. The formulas derived can be used to calculate the PPD simultaneously with, for example, the numerical calculation of a diffusion equation.
Topics: Models, Theoretical; Optics and Photonics; Photons
PubMed: 12095206
DOI: 10.1364/josaa.19.001383 -
Optics Express Feb 2016We proposed the world's first flexible ultrathin-body single-photon avalanche diode (SPAD) as photon counting device providing a suitable solution to advanced...
We proposed the world's first flexible ultrathin-body single-photon avalanche diode (SPAD) as photon counting device providing a suitable solution to advanced implantable bio-compatible chronic medical monitoring, diagnostics and other applications. In this paper, we investigate the Geiger-mode performance of this flexible ultrathin-body SPAD comprehensively and we extend this work to the first flexible SPAD image sensor with in-pixel and off-pixel electronics integrated in CMOS. Experimental results show that dark count rate (DCR) by band-to-band tunneling can be reduced by optimizing multiplication doping. DCR by trap-assisted avalanche, which is believed to be originated from the trench etching process, could be further reduced, resulting in a DCR density of tens to hundreds of Hertz per micrometer square at cryogenic temperature. The influence of the trench etching process onto DCR is also proved by comparison with planar ultrathin-body SPAD structures without trench. Photon detection probability (PDP) can be achieved by wider depletion and drift regions and by carefully optimizing body thickness. PDP in frontside- (FSI) and backside-illumination (BSI) are comparable, thus making this technology suitable for both modes of illumination. Afterpulsing and crosstalk are negligible at 2µs dead time, while it has been proved, for the first time, that a CMOS SPAD pixel of this kind could work in a cryogenic environment. By appropriate choice of substrate, this technology is amenable to implantation for biocompatible photon-counting applications and wherever bended imaging sensors are essential.
Topics: Metals; Optics and Photonics; Oxides; Photons; Probability; Semiconductors
PubMed: 26907030
DOI: 10.1364/OE.24.003734 -
Computer Methods and Programs in... Feb 2015The Monte Carlo method for photon transport is often used to predict the volumetric heating that an optical source will induce inside a tissue or material. This method...
The Monte Carlo method for photon transport is often used to predict the volumetric heating that an optical source will induce inside a tissue or material. This method relies on constant (with respect to temperature) optical properties, specifically the coefficients of scattering and absorption. In reality, optical coefficients are typically temperature-dependent, leading to error in simulation results. The purpose of this study is to develop a method that can incorporate variable properties and accurately simulate systems where the temperature will greatly vary, such as in the case of laser-thawing of frozen tissues. A numerical simulation was developed that utilizes the Monte Carlo method for photon transport to simulate the thermal response of a system that allows temperature-dependent optical and thermal properties. This was done by combining traditional Monte Carlo photon transport with a heat transfer simulation to provide a feedback loop that selects local properties based on current temperatures, for each moment in time. Additionally, photon steps are segmented to accurately obtain path lengths within a homogenous (but not isothermal) material. Validation of the simulation was done using comparisons to established Monte Carlo simulations using constant properties, and a comparison to the Beer-Lambert law for temperature-variable properties. The simulation is able to accurately predict the thermal response of a system whose properties can vary with temperature. The difference in results between variable-property and constant property methods for the representative system of laser-heated silicon can become larger than 100K. This simulation will return more accurate results of optical irradiation absorption in a material which undergoes a large change in temperature. This increased accuracy in simulated results leads to better thermal predictions in living tissues and can provide enhanced planning and improved experimental and procedural outcomes.
Topics: Hot Temperature; Monte Carlo Method; Optics and Photonics; Photons
PubMed: 25488656
DOI: 10.1016/j.cmpb.2014.11.007 -
Methods in Cell Biology 2003
Review
Topics: Animals; Electronics; Fluorescent Dyes; Humans; Image Processing, Computer-Assisted; Microscopy, Fluorescence; Optics and Photonics; Photobleaching; Photons; Time Factors
PubMed: 14719344
DOI: 10.1016/s0091-679x(03)72021-4 -
Optics Express Jun 2022We propose an approach to generate neuron-like spikes of vertical-cavity surface-emitting laser (VCSEL) by multi-frequency switching. A stable temporal spiking sequence...
We propose an approach to generate neuron-like spikes of vertical-cavity surface-emitting laser (VCSEL) by multi-frequency switching. A stable temporal spiking sequence has been realized both by numerical simulations and experiments with a pulse width of sub-nanosecond, which is 8 orders of magnitude faster than ones from biological neurons. Moreover, a controllable spiking coding scheme using multi-frequency switching is designed and a sequence with 20 symbols is generated at the speed of up to 1 Gbps by experiment. Furthermore, we investigate the factors related to time delay of spiking generation, including injection strength and frequency detuning. With proper manipulation of detuning frequency, the spiking generation delay can be controlled upto 60 ns, which is 6 times longer than the delay controlled by intensity. The multi-frequency switching provides another manipulation dimension for spiking generation and will be helpful to exploit the abundant spatial-temporal features of spiking neural network. We believe the proposed VCSEL-neuron, as a single physical device for generating spiking signals with variable time delay, will pave the way for future photonic spiking neural networks.
Topics: Lasers; Neural Networks, Computer; Neurons; Optics and Photonics; Photons
PubMed: 36224875
DOI: 10.1364/OE.456583 -
Optics Express Feb 2008We investigate nonlinear mid-infrared detection via two-photon transitions involving two bound subbands and one continuum resonance in an n-type multiple quantum well....
We investigate nonlinear mid-infrared detection via two-photon transitions involving two bound subbands and one continuum resonance in an n-type multiple quantum well. By varying the excitation energy, we have tuned the two-photon transition from resonant, yielding optimum resonant enhancement with a real intermediate state, to nearly-resonant, with a virtual but resonantly enhanced intermediate state. For autocorrelation purposes, the latter configuration improves time resolution whilst partially retaining a resonant enhancement of the two-photon transition strength.
Topics: Equipment Design; Equipment Failure Analysis; Infrared Rays; Microwaves; Optics and Photonics; Photons; Spectrum Analysis; Statistics as Topic; Transducers
PubMed: 18542228
DOI: 10.1364/oe.16.001523 -
Optics Express Jun 2010We demonstrate a method to improve the measurement sensitivity of two-photon frequency-domain lifetime measurements in poor signal to background conditions. This...
We demonstrate a method to improve the measurement sensitivity of two-photon frequency-domain lifetime measurements in poor signal to background conditions. This technique uses sinusoidal modulation of the two-photon excitation source and detection of the second harmonic of the modulation frequency that appears in the emission. Additionally, we present the mathematical model which describes how the observed phase shift and amplitude demodulation factor of two-photon phosphorescence emission are related to the phosphorescence lifetime and modulation frequency. We demonstrate the validity of the model by showing the existence of new frequency terms in the phosphorescence emission generated from the quadratic nature of two-photon absorption and by showing that the phase shift and demodulation match theory for all frequency components.
Topics: Energy Transfer; Equipment Design; Fluorescence; Luminescence; Luminescent Measurements; Nonlinear Dynamics; Optics and Photonics; Photons
PubMed: 20588496
DOI: 10.1364/OE.18.013631