Types Of Optical Cavities Research Articles

(Invited) Dynamics of Light-Matter Interactions in Plasmonic Optical Cavities for Characterizing Nanostructures Relevant to Energy Conversion and Photocatalysis

Optical cavities are an established means to increase light-matter interactions with a wide range molecules, nanostructures and bulk materials. The use of an optical cavity to increase the likelihood of photon absorption by a material has clear potential for being of value for optical energy conversion and photocatalysis. Furthermore, optical cavities can significantly alter excited state dynamics due to the potential for Purcell effects that increase radiative rates of emission of a given material, molecule, or nanostructure. These dynamic changes can serve as a sensing mechanism of cavity impact to photoprocesses, making characterization tools such as transient absorption and time-resolved emission measurements an effective means to probe the degree of light-matter coupling. Taken a step further, these characterization tools can help establish the degree of light-matter coupling necessary to control excited state lifetimes for a particular purpose or application. Here, we explore the dynamics of nanostructured systems coupled to, or made out of, plasmonic materials. Importantly, plasmonic structures are well-known to serve as a type of optical cavity, and though plasmonic cavities are lossier than their dielectric counterparts, they can also confine light to a small mode volume which is very helpful for increasing photonic interactions with nanostructures. The focus of this talk is on materials and nanostructures of interest for solar energy conversion or photocatalysis, such plasmonic nanoparticles and semiconducting nanoparticles, which are interacting with or functioning as, a plasmonic cavity. The plasmonic cavity can be as simple as a thin metal film that supports a propagating surface plasmon polariton (SPP). We also explore refractory plasmonic systems due to their potential durability and reduced likelihood of melting under optical illumination as compared to noble metal nanostructures. The dynamics of nanostructure photoprocesses as a function of photon energy relative to the cavity resonance is explored in detail and impact on applications is described. Work performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Silicon-Based Light-Emitting Devices Based on Ge Self-Assembled Quantum Dots Embedded in Optical Cavities

Highly efficient light-emitting devices operating in 1.3-1.6 μm wavelength range are realized by combining optical cavities and Ge self-assembled quantum dots (QDs) grown on SOI wafers by molecular beam epitaxy (MBE). Different types of optical cavities, including photonic crystal (PhC) nanocavities, microdisks, and microrings, are fabricated to enhance the light emission efficiency at room temperature. Sharp resonant peaks with Q-factor on the order of 103 are observed in the micro-photoluminescence (μPL) spectrum. Through numerical simulation, these peaks are well identified as the corresponding cavity modes. The emission performances of these devices are also investigated by performing pumping-power- and geometric-parameter-dependent μPL measurements. The resonant wavelength, Q-factor, and emission intensity can be easily manipulated by these parameters.

Photonic Laser Propulsion: Proof-of-Concept Demonstration

T HE propulsion concept of photonic propulsion (i.e., the direct transfer of the momentum of photons to a spacecraft that emits them) has been around since the beginning of the 20th century [1]. According to special relativity, the largest velocity of any kind of rocket exhaust particles is the velocity of light, c 2:99 10 m=s. Photons are the propellant with the largest specific impulse Isp 3:06 10 s, but with the smallest thrust-to-power ratio T=P 3:34 10 9 N=W. Photonic propulsion is highly inefficient in thrust generation at a given power. Thus, the applications proposed for its implementation require high-power photon beams and extremely large space platforms, with power generation from large solar collectors [2], nuclear power generators [3], or from antimatter power generators [4]. Implementation of these large complex systems is many decades away. One approach to enhance practicality of photonic propulsion involves overcoming its inherent inefficiency through amplification of photon momentum transfer. This may be accomplished by bouncing or trapping photons between two high-reflectance (HR) mirrors that form an optical cavity between two space platforms. There have been two types of optical cavities considered for this purpose: 1) passive resonant optical cavities and 2) nonresonant optical cavities. In a passive resonant optical cavity, a laser beam is injected into the cavity. Because the passive resonant optical cavity requires a high-power single-frequency laser (which is itself inefficient) for efficient power injection into the cavity, and because the passive resonant optical cavity is highly sensitive to small changes in cavity length [5] and deterioration in mirror quality, it is impractical for photonic propulsion. The sensitivity to cavity length was exemplified in a gravitational detection system with a high Q passive optical cavity, in which even a 1-nm perturbation in cavity length thwarted the resonance condition and canceled the force exerted on mirrors [6]. The nonresonant optical cavity approach [7,8], as in Herriot cells, requires tightly focused laser beam spots on each mirror to avoid the beam interference that may result in optical resonance in the cavity. However, as the cavity length and the number of laser beam reflections increase, the laser beam focal spot diameter projected on mirrors increases, which requires extremely large mirrors to avoid beam interferences. Once the laser beam spots start to interfere, the nonresonant cavity becomes the passive resonant cavity that is impractical for photonic propulsion. An attempt to demonstrate an amplified photonic propulsion concept based on the nonresonant optical cavity was performed by Gray et al. [9]. They reported measurement of an amplified photon thrust of 0:4 N using a 300Wcontinuous-waveNd:YAG laser and a photon thrust amplification factor of 2:6. The much-lower-than-expected performance probably resulted from the previously mentioned technical difficulties. Therefore, the previously proposed photonic propulsion concepts seemed to be impractical, and the search for a new viable photonic propulsion concept continues. Photonic laser propulsion (PLP) is a new and innovative photonic propulsion concept [10,11] that is based on forming an active resonant optical cavity between two space platforms. The laser gain medium is located in the optical cavity, in contrast to the passive resonant cavity concept, in which the laser gain medium is located outside of the optical cavity. In PLP, the photon thrust FT produced on each mirror is given by

A NOVEL TYPE OF OPTICAL OSCILLATOR BASED ON A LIQUID CRYSTAL GAIN MEDIUM

A nonlinear optical medium results by the collective orientation of liquid crystal molecules tightly coupled to a transparent photoconductive layer made of a thin photorefractive BSO crystal. For this new kind of liquid crystal light-valve, we have recently demonstrated signal beam amplification and self-pumped phase conjugation. After giving a description of the device and its properties, we show here that the liquid crystal light-valve, when inserted in a ring optical cavity, has a gain large enough to overcome the losses, thus resulting in unidirectional field oscillation. The wide transverse size and the high nonlinearity of the liquid crystal medium allow us to explore dynamical regimes where a huge number of longitudinal and transverse modes are simultaneously amplified in the cavity. Up to date, such regimes have remained inaccessible for all the known types of optical cavities. In particular, we report the observation of high amplitude spatiotemporal pulses appearing in random space points and confined along the three space directions. Then, we present a theoretical model that takes into account the longitudinal dependence of the field in the liquid crystal optical oscillator, and show that spatiotemporal pulses confined in 3D space directions arise from the random superposition of many longitudinal and transverse modes oscillating at different frequencies.

Accurate three-dimensional modal solutions for optical resonators with periodic layered structure by using the finite element method

Accurate vector finite element solutions for three-dimensional (3-D) axisymmetric multilayered optical cavities are presented. Resonating wavelength and field profiles are shown for the fundamental and higher order modes for different types of optical cavities. The work has shown that for a narrow multilayered cylinder of diameter /spl les/0.5 /spl mu/m, for miniature vertical cavity surface emitting lasers (VCSEL), which is a popular class of laser showing favorable performance characteristics, the effect of waveguide dispersion is an important factor. This causes a blue shift of the output wavelength, requiring an adjustment to the layer thickness in the system design, to achieve the desired wavelength. The results of the simulation show close agreement with features obtained through experimental investigations.

Intracavity second-harmonic generation of chemical oxygen-iodine laser emission using a LBO crystal

Intracavity second-harmonic generation of continuous-wave chemical oxygen-iodine laser emission has been studied. A chemical oxygen-iodine laser with a maximum fundamental-wave output power of about 10 W in a concentric cavity was used. Experiments were performed for three types of optical cavities using an 1 cm LBO crystal. Second-harmonic output of 12.4 W, 6.2 W, and 5.2 W, effective extraction efficiencies of 155.0% 65.9%. and 55.3%, and single-pass conversion efficiencies of 0.615%, 0.685%, and 0.655% were obtained for the respective cavities. A comparison of these results of coupling by frequency doubling with the results of fundamental-wave output coupling of this system is also presented.

FELS, a 3-dimensional FEL simulation code including storage-ring operation of high-gain FELS

Abstract The free-electron-laser code FELS is a program to model a high-gain free-electron laser in the short-wavelength long pulse regime. The code can be run to describe the single-pass amplifier operation, and the oscillator configuration. Two different types of optical cavities are implemented, the nearly concentric and the ring resonator. Furthermore, the modelling not only of operation with linacs but also with storage ring devices is included. Two versions provide calculation with and without the harmonics of the spontaneous undulator spectrum included [1,2]. This paper will review the models of the FEL, the optical resonator, and the storage ring, and the implementation of the code, shortly. Furthermore, simulation results which point out the differences between ID, 2D and 3D calculations for the example of FELICITA II, the second FEL experiment at DELTA, are included [3,4].

Optical cavities for free electron lasers

Most early free electron laser (FEL) designs used simple optical cavities consisting of two concave dielectric mirrors. This type of optical cavity, though appropriate for proof of principle experiments, does not take advantage of the unique features of the FEL gain medium such as broadband tunability, high peak and average power and access to previously inaccessible wavelength ranges. This article will discuss various approaches which have been demonstrated or are under development to take advantage of these aspects of the FEL gain medium. The prospects and problems for each approach will be discussed. Broadband cavities have been demonstrated using holes in the mirrors, Brewster plate output coupling and a suspended intracavity mirror. High power designs using ring resonators and grazing incidence mirrors are now being developed. Access to the soft X-ray region may be accomplished using a whispering gallery ring resonator. The gain medium of the FEL does not store energy. Because of this fact, the peak power can only be increased by cavity dumping. Several techniques will be discussed which accomplish this. Interferometric and dispersive cavities are being studied to tailor the spectral or temporal behavior of the laser to a given specification. Finally, several new schemes will be presented which hold promise as future optical cavities for FELs.

Monolithically integrated transverse-junction-stripe laser with an external waveguide in GaAs/AlGaAs

This device consists of a five-layer transverse-junction-stripe laser structure monolithically integrated with an external three-layer waveguide. The transverse p-n junction within the laser cavity permits the use of a vertical p-n junction in the external waveguide for future implementation of a modulator without disturbing the laser operation. As a result, this structure allows for flexibility in the design of the external waveguide/modulator without resorting to complicated regrowth procedures. Design curves for two different types of optical cavities are presented, and the reflectivity and transmission of the etched facet as a function of active layer thickness is modeled in detail using an excitation field approach. Finally, integrated laser/waveguide devices are fabricated based on this design and are compared to the theoretical curves. Most devices had threshold currents between 60 and 80 mA, while laser-to-waveguide transmission coefficients were as high as 38%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Eigenmodes of Kerr-type phase-conjugate mirrors

The equivalence of the reflection-invariant modes of an imperfect phase-conjugate mirror to the transverse modes of a particular type of optical cavity is demonstrated. The reflection-invariant modes are shown to satisfy an approximate minimum-volume condition when the pump and the probe beams are well aligned.