Laser Beam Steering Research Articles

Fast targeted gene transfection and optogenetic modification of single neurons using femtosecond laser irradiation

A prevailing problem in neuroscience is the fast and targeted delivery of DNA into selected neurons. The development of an appropriate methodology would enable the transfection of multiple genes into the same cell or different genes into different neighboring cells as well as rapid cell selective functionalization of neurons. Here, we show that optimized femtosecond optical transfection fulfills these requirements. We also demonstrate successful optical transfection of channelrhodopsin-2 in single selected neurons. We extend the functionality of this technique for wider uptake by neuroscientists by using fast three-dimensional laser beam steering enabling an image-guided “point-and-transfect” user-friendly transfection of selected cells. A sub-second transfection timescale per cell makes this method more rapid by at least two orders of magnitude when compared to alternative single-cell transfection techniques. This novel technology provides the ability to carry out large-scale cell selective genetic studies on neuronal ensembles and perform rapid genetic programming of neural circuits.

Monolithic QW laser beam steering and wavelength tunability

We demonstrate a monolithic tunable laser on a QW structure by integrating an optical beam steering section with an area-selectively intermixed QW gain section. Wavelength switching is achieved by steering the laser beam over an optical gain medium that consists of two laterally adjacent quantum well regions selectively intermixed to varying extents. The device output had a total of 10 nm wavelength tuning that was controlled by injecting separate electrical current values to each of the steering contacts and the amplifier contact.

Fast and precise Laguerre–Gaussian beam steering with acousto-optic deflectors

Novel fluorescence microscopy techniques and two-color laser direct imaging photolithography methods that enable resolution an order of magnitude beyond the diffraction limit require Laguerre-Gaussian beams and a fast and precise laser beam steering device to obtain images and produce microstructures. An acousto-optic deflector (AOD) is a suitable choice and provides high-speed random access beam positioning with subnanometer precision as well as beam intensity control in a single element. In high-resolution applications, the impact of an AOD on beam quality plays a major role. We study the transfer function of an AOD for a fundamental Gaussian and a doughnut-shaped Laguerre-Gaussian beam by measuring the beam quality as a function of the diffraction angle after passing through the device. It is demonstrated that an AOD introduces negligible distortion and degradation to the beam profile and is therefore highly suitable for use in super-resolution imaging and photolithography techniques where manipulation of Laguerre-Gaussian doughnut-shaped beams is required.

Raman and SERS microscopy for molecular imaging of live cells

Raman microscopy is a promising technology for visualizing the distribution of molecules in cells. A challenge for live-cell imaging using Raman microscopy has been long imaging times owing to the weak Raman signal. Here we present a protocol for constructing and using a Raman microscope equipped with both a slit-scanning excitation and detection system and a laser steering and nanoparticle-tracking system. Slit scanning allows Raman imaging with high temporal and spatial resolution, whereas the laser beam steering system enables dynamic surface-enhanced Raman imaging using gold nanoparticles. Both features enable mapping of the distributions of molecules in live cells and visualization of cellular transport pathways. Furthermore, its utility can be expanded to small-molecule imaging by using tiny Raman-active tags such as alkyne. For example, DNA synthesis in a cell can be visualized by detecting 5-ethynyl-2'-deoxyuridine (EdU), a deoxyuridine derivative with an alkyne moiety. We describe the optics, hardware and software to construct the Raman microscope, and discuss the conditions and parameters involved in live-cell imaging. The whole system can be built in ∼8 h.

Laser Beam Steering not only in Ophthalmology

AbstractLasers are versatile tools. Nowadays, they are just as indispensable in materials processing as in eye surgery or super high resolution microscopy. The different areas of application have similarities, however, since a precise positioning of the laser beam is always crucial. At the same time, this laser beam steering and focusing also requires the drive systems used to be dynamic, reliable and compactly dimensioned, in order to allow simple integration in applications. It is therefore hardly surprising that piezoelectric drive components often have no serious alternative for laser beam steering.

A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell

A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell (T-PNLC) is demonstrated. T-PNLC consists of three layers. Liquid crystal (LC) directors in the two layers near glass substrates are orthogonal to each other and those two layers modulate two eigen-polarizations of an incident light. As a result, two eigen-polarizations of an incident light experience the same phase shift. In the middle layer, LC directors are perpendicular to the glass substrate and contribute no phase shift. The phase shift of T-PNLC is electrically tunable and polarization-independent. T-PNLC does not require any bias voltage for operation. The phase shift is 0.28 π rad for the voltage of 30 Vrms. By measuring and analyzing the optical phase shift of T-PNLC at the oblique incidence of transverse magnetic wave, the pretilt angle of LC directors and the effective thickness of three layers are obtained and discussed. The potential applications are spatial light modulators, laser beam steering, and micro-lens arrays.

Femtosecond laser-induced phase modulation based on KTP crystal

The femtosecond laser-induced phase modulation based on KTP crystal is demonstrated. The phase modulation in femtosecond laser irradiated area is deduced through Drude model and color centers model, and the phase shift was also measured by cyclic radial shearing interferometer. As a result, a phase modulator with 2π phase shift is achieved using a 2.5-mm-thick KTP crystal and femtosecond laser pulses, and the spatial distribution of phase shift was also given. Such approach will be of great potential values for optical cross-connect switching, laser beam steering, low-cost electro-optic sensor, adaptive optics, coherent beam combination.

A polarization independent liquid crystal phase modulation adopting surface pinning effect of polymer dispersed liquid crystals

A polarization-independent liquid crystal (LC) phase modulation using the surface pinning effect of polymer dispersed liquid crystals (SP-PDLC) is demonstrated. In the bulk region of the SP-PDLC, the orientations of LC directors are randomly dispersed; thus, any polarization of incident light experiences the same averaged refractive index. In the regions near glass substrates, the LC droplets are pinned. The orientations of top and bottom droplets are orthogonal. Two eigen-polarizations of an incident light experience the same phase shift. As a result, the SP-PDLC is polarization independent. Polarizer-free microlens arrays of SP-PDLC are also demonstrated. The SP-PDLC has potential for application in spatial light modulators, laser beam steering, and electrically tunable microprisms.

Note: High capacity digital laser beam steering system

The combination of liquid crystal cells with polarizing cube beam splitters has been used to direct a beam of light to multiple directions. The polarization at each beam splitter is controlled by applying a signal to a corresponding liquid crystal cell. Ten cascaded stages have deflected a HeNe laser beam to 1024 digitally selectable angles.

Neural network controller for Tunable Liquid Crystal Photonic Device work as Laser Beam Steering Device

In this paper, artificial neural network controller (NNC) was designed and used to adjust and control the work of the laser beam steering device consist of liquid crystals cell and other optical components. The target of the neurocontroller is to guarantee smooth deliver and exactly control the laser beam to a required location via control the liquid crystals cell and the optical components. Back propagation method is used to build up the neurocontroller, main artificial neurocontroller software is consists of three sub programs according to the three functions it proposed to administer. Trial results obtained after the execution of the neurocontroller affirmed the optimum performs in administrating, controlling and standardize the device while the value of the errors reached its minima, which coincidence with the approaches of the paper goals. Keyword Neural network; neurocontroller; Laser beam steering.

Third-order theory of the Risley-prism-based beam steering system

Nonparaxial ray tracing is performed to investigate the field scanned out by a single beam through two rotatable thick prisms with different parameters, and a general solution is obtained and then expanded into a power series to establish the third-order theory for Risley prisms that paves the way to investigate topics of interest such as optical distortions in the scan pattern and an analytical solution of the inverse problem of a Risley-prism-based laser beam steering system; i.e., the problem is concerned with how to direct a laser beam to any specified direction within the angular range of the system.

Two-Dimensional MEMS Stage Integrated With Microlens Arrays for Laser Beam Steering

A novel microelectromechanical stage with one uniaxial set of combs capable of 2-D actuation is presented. A polymer microlens array (MLA) is mounted vertically onto the stage. Driven at resonance, the stage deflects 124 μm out of plane and 34 μm in plane. Finally, laser beam steering is demonstrated using two cascaded MLAs.

Electronically Controlled Two-Dimensional Steering of In-Phase Coherently Coupled Vertical-Cavity Laser Arrays

Photonic crystal vertical-cavity surface-emitting laser arrays can be designed to lase only in the in-phase array supermode. By electronically addressing the array elements independently, the relative phases between the emission from each element can be altered. The shift in relative phase results in the angular deflection of the central peak of the in-phase array supermode. We demonstrate highly controllable steering of a coherent laser beam produced by a 2 2 array of emitters.

On the fabrication of three-dimensional silicon-on-insulator based optical phased array for agile and large angle laser beam steering systems

In this article, the authors present and discuss the fabrication of three-dimensional (3D) optical phased array (OPA) devices for large angle, two-dimensional optical beam steering. Fabrication of a single layer (one-dimensional) OPA prototype for one-dimensional beam steering on silicon nanomembrane is presented. The authors present different approaches, such as nanoimprint lithography, optical lithography, and self-aligned patterning of multibonded silicon-on-insulator wafers, for the realization of 3D OPA devices in particular and 3D photonic circuits in general. At the end, the authors discuss the challenges and potential solutions.

Beam Pointing Precision Control by Using a Liquid Crystal Optical Phased Array

For laser beam steering, a pure optical-electric system without mechanical or inertial parts is used. The new device is a Liquid Crystal Optical Phased Array (LCOPA). Supplying electric field to liquid crystal cell with electrodes, the extraordinary refractive index changes, which results in phase shift that modulates the direction of incident beam. The advantages of this device are small size, less energy consuming, programmable and addressable control. A one dimensional device is designed and tested. The resolution of the steering angle is 20 μrad, the range is ±2o. The effect of flyback region and phase valley on diffraction efficiency is also discussed briefly.

Ultra-Compact Laser Beam Steering Device Using Holographically Formed Two Dimensional Photonic Crystal

In this paper, we report the theoretical study of polymer-based photonic crystals for laser beam steering which is based on the superprism effect as well as the experiment fabrication of the two dimensional photonic crystals for the laser beam steering. Superprism effect, the principle for beam steering, was separately studied in details through EFC (Equifrequency Contour) analysis. Polymer based photonic crystals were fabricated through double exposure holographic interference method using SU8-2007. The experiment results showed a beam steering angle of 10 degree for 30 nm wavelength variation.

High-resolution laser lithography system based on two-dimensional acousto-optic deflection

We present an advanced high-resolution, compact laser lithography system for fast prototyping of complex integrated optics devices comprising microring resonators and photonic crystal structures. Precise and flexible structuring of photoresist patterns is achieved by combing three linear stages (xyz) for sample positioning and a two-dimensional acousto-optical deflector for laser beam steering and intensity control. A continuous wave diode laser operating at a wavelength of 375 nm is used to illuminate all types of photoresists including SU-8. Using a microscope objective with a numerical aperture of 1.40, structure widths of approximately 200 nm can be obtained. The write-field covered by acousto-optic deflection can be as large as 200x200 microm(2) when using an objective with a focal length of 4.5 mm. With a two-step lithography process, gaps as small as 150 nm between adjacent structures have been achieved, yielding superior photoresist masks for microring resonators with coupling ports.

Multiplexed broadband beam steering system utilizing high speed MEMS mirrors

We present a beam steering system based on micro-electromechanical systems technology that features high speed steering of multiple laser beams over a broad wavelength range. By utilizing high speed micromirrors with a broadband metallic coating, our system has the flexibility to simultaneously incorporate a wide range of wavelengths and multiple beams. We demonstrate reconfiguration of two independent beams at different wavelengths (780 and 635 nm) across a common 5x5 array with 4 micros settling time. Full simulation of the optical system provides insights on the scalability of the system. Such a system can provide a versatile tool for applications where fast laser multiplexing is necessary.

Polarisation‐independent liquid crystal devices

Liquid crystal (LC) devices can be used as amplitude modulators and phase modulators. Most LC devices are polarisation‐dependent and require at least one polariser. As a result, the optical efficiency is greatly reduced. In this paper, we review some of our recently developed polarisation‐independent LC devices. For amplitude modulation, we report two polariser‐free devices which combine light scattering with dye absorption: dye‐doped polymer‐dispersed liquid crystal (PDLC) and dye‐doped LC gels. For phase modulation, we also present two examples: residual phase type, e.g., voltage‐biased PDLC, Polymer‐Stabilised Cholesteric Texture (PSCT), and homeotropic LC gels; and double‐layered structure, such as thin polymer film‐separated orthogonal LC layers, and double‐layered LC gels. Potential applications of these polarisation‐independent LC devices for displays, laser beam steering and adaptive optics are emphasised.

Air-coupled laser vibrometry: analysis and applications

Acousto-optic interaction between a narrow laser beam and acoustic waves in air is analyzed theoretically. The photoelastic relation in air is used to derive the phase modulation of laser light in air-coupled reflection vibrometry induced by angular spatial spectral components comprising the acoustic beam. Maximum interaction was found for the zero spatial acoustic component propagating normal to the laser beam. The angular dependence of the imaging efficiency is determined for the axial and nonaxial acoustic components with the regard for the laser beam steering in the scanning mode. The sensitivity of air-coupled vibrometry is compared with conventional "Doppler" reflection vibrometry. Applications of the methodology for visualization of linear and nonlinear air-coupled fields are demonstrated.