bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-Assisted Scanning Tunneling Microscopy
Authors: Völcker Martin , Krieger Wolfgang , Walther Herbert
Published: February 2023

The scanning tunneling microscope (STM) was the starting point for the development of numerous new methods to obtain atom-resolved surface information. In the usual mode the STM produces images of the local density of states at the surface. New modifications of the STM allow the generation of surface images with quantities such as atomic forces, photon emission, temperature, and ion conductance, as well as images with spectroscopic information. In some of these experiments new modes of operation have been introduced where the distance dependence of these quantities is used to control the width of the tunneling gap of the STM.
Optical Image Recognition System Implemented with a 3-D Memory Disk
Authors: Psaltis Demetri , Li Sidney , Qiao Yong , Curtis Kevin
Published: February 2023

We will discuss the use of non-linear optical materials for the implementation of memories and the use of such memories in image processing. Specifically, we will describe holographic 3-D disks constructed with photorefractive crystals or photopolymers. We will discuss how the material properties affect the performance of such memories and we will describe dynamic copying methods that can provide non-destructive read-out and selective erasure and replacement of information. Finally, we will describe the implementation of a face recognition system using the 3-D disk.
Bifurcating Neuromorphic Optical Pattern Recognition in Photorefractive Crystals
Authors: Liu Hua-Kuang
Published: February 2023

Pattern recognition methodology is extremely important for robotics vision applications especially in the present era of automation. Perhaps one of the most well-known and important class of techniques of pattern recognition is the Vander Lugt matched filter correlator1 and its related methods2-3. In the optical implementations of the matched filter correlator, the technique involves the storage of the Fourier transform, via a thin lens, of the amplitude and phase of an image in a recording medium and later addressing the stored information by the Fourier transform of a new input. When the inverse Fourier transform of the multiplication of the two Fourier transforms are taken, cross-correlation between the new input and the stored is obtained. The cross—correlation intensity is a measure of the similarity between the two images. In the digital implementations, the Fourier transform operation is accomplished sequentially by electronics instead of the parallel transformation of a thin lens. Although the matched filter method is effective in recognizing an input image with the advantage of shift invariant, the question of whether the process emulates biological vision process is difficult if not impossible to answer.
Multiphoton Ionization of Atoms and Molecules
Authors: Corkum P. B. , Dietrich P. , Laberge M.
Published: February 2023

Ionization of diatomic molecules should be described by the same basic theories as atomic ionization. For example, one might expect many common elements in a theory describing multiphoton ionization of HCl and of Argon. We will show that, for the first ionization step, atomic models require little or no modification to accurately describe molecular ionization, but we will also show that the large Stark shifts and large polarizability of molecular ions forces us to modify atomic models for higher charge states.
Quantum Noise and Its Reduction in Phase Conjugators
Authors: Wu Weishu , He Q. Byron , Yeh Pochi , Gu Claire
Published: February 2023

The fidelity of optical phase conjugation is an important issue in many applications. To increase the fidelity, it is necessary to understand the physical origin of the quantum noise and to develop techniques to reduce the fluctuation.
Formation of Spatial Structures in a Nematic Liquid Crystal Film with Single Feedback Mirror
Authors: Santamato E. , Tamburrini M. , Bonavita M. , Wabnitz S.
Published: February 2023

Spontaneous spatial instabilities have been predicted and observed in Kerr nonlinear media plugged into suitable optical resonator1. A similar effect was also reported in a nematic liquid crystal film.2
Optical Squeezing with Self-Phase-Stabilized Scheme
Authors: Shirasaki M. , Doerr C. R. , Bergman K. , Haus H. A.
Published: February 2023

A nonlinear symmetric Mach-Zehnder interferometer was proposed for optical squeezing1,2, and it was shown that a nonlinear ring reflector with optical pulses is a practical realization of this squeezer2 (see Fig.1). Noise suppression in a balanced homodyne detection using this squeezing scheme was observed experimentally3,4.
Numerical modelling of transverse SRS and SBS in large-aperture high-power optical components
Authors: Sacks R. A. , Dixit S. N.
Published: February 2023

As presently envisioned, the Nova Upgrade project will employ large aperture final optics that are exposed to multi-nanosecond pulses at several GW/cm2 intensities. Propagation of such high-power long-duration laser pulses through large-aperture optics can drive significant amounts of Raman and Brillouin scattering in the transverse direction within the optics. Such scattering can lead to energy loss from the pump and hence degradation of system performance. More critically, the scattered light can reach fluences sufficient to cause optical and/or mechanical damage to the optics. Transverse SBS has been observed on Nova and has been suppressed by adding a small amount of bandwidth to the pump [1].
Analysis of The Thick Medium Z-Scan
Authors: Hermann J.A.
Published: February 2023

An analytic solution of the propagation equation for a symmetrical optical beam has been obtained, in the situation where the beam is focused within an optically nonlinear medium having a thickness greater than the depth of focus. Previous related work by the author has concentrated upon finding solutions, in continued-fraction format, within the strongly self-focusing/defocusing limit [1]. In the present work, an expression is derived for the transmitted electric field envelope in the weakly nonlinear case. The result is described in terms of a linear superposition of Gaussian-Laguerre modes, the coefficients of which depend only upon the linear component of the accumulated optical phase on the optic axis. The medium that has been explored possesses a Kerr-type susceptibility with refractive and absorptive components.
Optical Didode Effect in Mn:KNSBN Crystal
Authors: She Weilong , Wu Qi , Li Qingxing , Yu Zhenxin , Zhang Qinglun , Chen Huanchu
Published: February 2023

Resently, a kind of induced optical diode effect has been observed by using two colliding He-Ne laser beams in Mn doped KNSBN crystal[1]. In this paper, we report the time characteristic of optical diode effect.
Method of integral equations and extinction theorem in volumetric and surface phenomena in nonlinear optics
Authors: Ghiner A.V. , Surdutovich G.I.
Published: February 2023

The method of integral equations of molecular optics [1] is based on the representation of the medium as the system of discrete oscillators and gives self-consistent description of the electromagnetic phenomena in medium without using operation of averaging when one comes from micro to macro-scopic field. In [2] the attempt has been made to apply method of integral equations to the nonlinear optics within the limits of the conception of local (microscopic) field. For justification of the corner-stone assumption that non-lineal polarization satisfies the wave equation it is necessary to assume the number of rather strict restrictions — plane pumping wave, plane interface between the media, approximation of given field and so on. In [3] this problem was solved in a general case without the above-mentioned assumptions but only for nonmagnetic medium with dipole mechanism of nonlinearity.
Recent Advances in Ultra Long Distance Soliton Transmission
Authors: Mollenauer L. F.
Published: February 2023

The last few years have seen a veritable explosion of ideas for the better implementation of ultra long distance soliton transmission. Experimental proof is only just now beginning to catch up. For example, by using a recirculating loop, we have recently been able to demonstrate "error-free" (measured bit error rate ≤10–10) soliton transmission over more than 15,000 km at 5 Gbit/s, single channel, and over more than 12,000 km at 10 Gbit/s in a two-channel WDM (wavelength-division-multiplexing) [1]; see Fig. 1. These results, however auspicious, represent just a beginning. With the implementation of certain ideas, tested so far only in simulation, the bit rate for such error-free, ultra long distance transmission is expected soon to rise to several tens of Gbit/s.
Nonlinear Optical Properties of Narrow-Gap Type-II Superlattices
Authors: Youngdale E. R. , Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Wang W. I.
Published: February 2023

We report here the first experimental and theoretical investigation of free carrier nonlinear optical processes in Type-II superlattices with narrow energy gaps. A general analysis of the effects of semiconductor band structure on nonlinear response at long wavelengths shows that the most favorable nonlinearities may be achievable in heterostructures with an indirect band alignment, where the indirectness may be in either real or momentum space.1 One of the most relevant figures of merit for devices is An/a, where An is the nonlinear modulation of the index of refraction and a is the absorption coefficient. However, An is limited in narrow-gap materials such as Hgo.78Cdo.22Te because the large third-order nonlinear susceptibilities (y(3)) observed at CO2 wavelengths tend to severely saturate at high intensities due to the dynamic Burstein shift.2
Optical Parametric Oscillation with Intracavity Sum-Frequency Generation
Authors: Moore Gerald T. , Koch Karl
Published: February 2023

We present theoretical calculations of an optical parametric oscillator (OPO) containing, in addition to the OPO crystal, a crystal for intracavity sum-frequency generation (SFG). The latter crystal combines light at the pump frequency ω
p
with light at the OPO signal frequency ω
s
to produce the desired frequency ω
d
= ω
p
+ ω
s
. Only the frequency ω
s
oscillates in the cavity. This system is modeled in the plane-wave approximation for both spatial orderings of the crystals. The pump power is ultimately converted to the desired radiation, to idler radiation of frequency ω
i
=2ω
p
– ω
d
, and to cavity losses at frequency ω
s
. Since the ω
i
and ω
d
radiation grows from zero on each pass, changes in the cavity length do not produce interference effects. The choice of crystal for the OPO is limited by the requirement that this crystal transmit the long-wavelength idler. With proper choice of design parameters, little pump power remains unconverted by the two crystals over an extended range of the incident pump intensity. In steady-state operation the ratio η of the photon flux emitted at ω
d
to the photon flux incident at ω
p
can be nearly 0.5.
Ferroelectric-Liquid-Crystal Controlled Anisotropie Second-Harmonic Generation
Authors: Marowsky G. , Heinemann E. , Pinnow M. , Kreuzer F.H. , Leigeber H. , Miller A.
Published: February 2023

Due to their spontaneous polar order and high degree of alignment ferroelectric liquid-crystals have recently attracted great interest as promising nonlinear materials. In particular thin layers of chiral (smectic-C*) molecules sandwiched between two glass slides (cf. Fig. 1) are considered as practical device concepts exhibiting bulk nonlinear response. We have applied optical second-harmonic generation (SHG) to unravel the mechanism of alignment of the liquid-crystalline matrix - a commercial liquid crystal mixture - and its interaction with an added siloxane of high second-order nonlinearity /1/, whose chemical structure is also indicated in Fig. 1.
Four-Wave Mixing and Optical Modulation in Laser Diodes
Authors: Simpson T.B. , Liu J.M.
Published: February 2023

Nearly-degenerate four-wave mixing in laser oscillators has attracted much recent attention.[1-4] In laser diodes, the interaction has usually been described by models emphasizing the spatial dependence of the nonlinear coupling.[2] Alternatively, injection locking of laser diodes is most often described by models emphasizing the optical resonance of the laser cavity and the time dependence of the interaction.[5] Both situations, however, represent nearly identical experimental configurations and little effort has been made to connect the two pictures. Recent four-wave mixing experiments in an argon-ion laser have been modeled using the lumped-circuit rate-equation formalism[3] and an earlier rate-equation analysis was shown to be consistent with laser diode four-wave mixing data.[4]
Fundamental materials and device issues for digital holographic data storage
Authors: Hesselink Lambertus , Heanue John F. , Bashaw Matthew C. , Daiber A. J. , Snyder R.
Published: February 2023

The performance of digital holographic data storage (DHDS) systems is primarily limited by the recording medium, as other components have been developed for consumer applications. In this invited paper we review state-of-the-art DHDS systems, fixing issues, and fundamental tradeoffs between materials and device characteristics. Recent results, including stored and retrieved video clips will be presented.
Optical implementation of composite filters as volume holograms in LiNbO3 for pattern recognition
Authors: Hudson Tracy D. , Kransteuber Amy S. , McMillen Deanna K. , Yu Francis T. S. , Yin Shizhuo
Published: February 2023

The optical correlator originally proposed by Vander Lugt [1] has been extensively investigated as a laboratory novelty but not widely employed in application-specific pattern recognition systems. This result is due in part to the classical matched filter being sensitive to rotation and scale variations of the imagery. Two major avenues of approaching this image distortion limitation are currently being pursued.
Switchable Diffractive Elements and Applications to Holographic and Multi-layer Optical Storage
Authors: Domash Lawrence H. , Gomatam Badri N. , Leger James , Kilby Gregg
Published: February 2023

Electrically switchable holograms or diffractive optical elements have recently been demonstrated in a fine-grained polymer dispersed liquid crystal material, giving a basis for a new family of compact, nonmechanical wavefront control devices well suited for applications in optical data storage. Examples of potential applications for both holographic volume storage and multilayer disk storage systems will be presented, and current experimental status summarized.
Mobile Ion Compensation in Photorefractive Media for Multiplex Holography
Authors: Bashaw M. C. , Heanue J. F. , Hesselink L.
Published: February 2023

Volume holography is an important candidate for data storage and data processing applications. Its advantages lie in the inherent high capacity of volume memory, fast access due to optical addressing, and fast transfer rates due to the parallel nature of holography [1]. Multiple holograms, or data pages, may be stored using angular multiplexing, wavelength multiplexing, and related techniques. Capacity is determined by the angular bandwidth of the signal, the number of holographic pages, and the acceptable level of noise due to crosstalk and other sources present in the system. Volume holography is also an important candidate for optical interconnects and wavelength division multiplexing in communications and computing systems. Frequently, the same criteria required for data storage coincide with those required for other applications.
Distinction between lasing without inversion and parametric nonlinear optics
Authors: Mossberg Thomas W.
Published: February 2023

Many optical devices have the capacity to amplify light beams. Some of these devices are referred to as lasers. Some are referred to as wavemixing or parametric devices. Still others, such as driven two-level atoms, are frequently described as wavemixing devices but, in many instances, are actually lasers.
Nonlinear Optics Using Electromagnetically-Induced Transparency
Authors: Hakuta K.
Published: February 2023

Recently, there has been increasing interest on the idea of controlling optical responses using atomic-coherence or quantum-interferences. Typical example may be the concept of electomagnetically-induced transparency (EIT) [1]. The key idea of EIT is to apply a strong-coupling field between a metastable and upper states to dress them equivalently as two states decaying to a common level or continuum, and to induce the transparency at the split-center of Autler-Townes components. This idea of EIT may open new possibilities to various coherent processes, such as lasing without population inversion, enhanced refractive index without absorption], slow group velocity without absorption, enhanced nonlinearity without absorption, etc.
The Bright Future of Darkness in Nonlinear Optics
Authors: Swartzlander G. A. , Law C. T.
Published: February 2023

Dark solitons are often overshadowed by bright solitons when optical solitons are discussed, perhaps because they have proven more difficult to control and utilize. Whereas a single bright soliton is formed by a simple packet of light, a dark soliton requires a phase difference between two parts of the packet. The extra effort of controlling the phase, however, allows new and unexpected opportunities. For example, arrays of two-dimensional vortex solitons having no bright soliton analogy are possible. When used as bits of information, dark solitons may be more closely spaced than bright solitons in a one-dimensional system. What is more, dark solitons may, in principle, be observed in weakly nonlinear media because there is no threshold intensity. When consideration is given to light-controlling-light, dark solitons have the advantage that a bright signal may be guided or modulated in a dark region. Dark spatial solitons have been mostly investigated in nonlinear refractive media [1], although they have recently been reported in photorefractive media under a voltage bias.
Comparison of Wide-Band Electro-Optic Frequency Tuning in LiNbO3 and KNbO3 OPO's
Authors: Ewbank M. D. , Rosker M. J.
Published: February 2023

Typically, wavelength tuning in a birefringently phase-matched optical parametric oscillator (OPO) is accomplished by adjusting the angle of propagation in the nonlinear optical crystal. However, angle tuning is not the only way to alter the wavelength of an OPO; other physical mechanisms such as temperature, pressure or electric field1,2 that change the refractive indices (or more specifically, the birefringence) will induce a corresponding dispersion-compensating change in wavelength to maintain phase matching. Electro-optically tuning an OPO is particularly attractive since it is non-mechanical (does not involving any moving parts) and can be done rapidly. Previously, electro-optic tuning was used to compensate for the phase mismatch from self-heating in CD*A during second-harmonic generation.3 More recently, frequency stabilization in a doubly-resonant OPO configuration with KTP was accomplished using electro-optic tuning.4 Here, we describe the first demonstration of broadband wavelength tuning in an OPO via the electro-optic effect in LiNbO3. The method is then applied to KNbO3 since it has much larger electro-optic coefficients. A comparison of electro-optic tuning range and tuning rate for LiNbO3 and KNbO3 are also discussed.
Energy characteristics of a loop laser with a thermal holographic mirror using millisecond pulses at 1.06 μm
Authors: Betin A. A. , Matthews S. C. , Mangir M. S.
Published: February 2023

We report on experimental studies of a four-wave mixing thermal nonlinearity loop (TNL) conjugator for Nd: YAG laser operating at 1.06 μm with a 1 msec pulse format.
Experimental Demonstration of an Optical Neural Network Using Self-Defocusing Media
Authors: Skinner Steven R. , Cruz-Cabrera Alvaro A. , Steck James E. , Behrman Elizabeth C.
Published: February 2023

Artificial neural networks are becoming more common because they can do tasks that are difficult, or even impossible, for a common numerical processor. Their strength, compared with normal numerical processors, resides in the use of a very large number of simple processing elements that are highly interconnected. A typical artificial neural network mimics some behavioral characteristics of a brain, for example it is trained not programmed.
Non-Reciprocity of Polarization Rotatory Power
Authors: Bennett P.J. , Dhanjal S. , Svirko Yu. P. , Zheludev N. I.
Published: February 2023

It was commonly believed that polarization plane rotation in a non-magnetic, optically active media is reciprocal. Here we report, what is to the best of our knowledge, the first observation of nonreciprocal polarization plane rotation in an optically active, nonmagnetic crystal. We saw that a light wave which passed through the crystal, B12SO20, and which was then reflected exactly back through it, did not recover its initial polarization azimuth. The nonreciprocal component of rotation was of the order of 7×10-3 of the reciprocal rotation. The effect is unambiguous evidence of broken reversality of the light-matter interaction process. Our interest in this research was motivated by the fundamental importance of the topic, and because time non-reversal effects may be exploited in unidirectional valves for electromagnetic radiation.
Modeling CW, Bulk Periodically Poled LiNbC3 Optical Parametric Oscillators With Strong Idler Absorption
Authors: Lowenthal Dennis D.
Published: February 2023

An analytical model was developed to predict the performance of cw, singly resonant, optical parametric oscillators with strong idler absorption, strong pump depletion and thermally induced dephasing. Optimum beam sizes for a given crystal length are chosen consistent with the Boyd and Kleinman approach. Comparisons are presented with existing data and full diffraction code modeling with good agreement. In some cases idler absorption enhances the pump depletion by impeding back conversion.
Generalized Dispersion Equations for Nonlinear Waveguides with Kerr-type Films
Authors: Jeong Jong-Sool , Song Seok Ho , Lee El-Hang
Published: February 2023

The characteristics of planar waveguides with nonlinear layers has been extensively studied due to their potential application as all-optical switching and signal-processing element [1-3]. Here we present a generalized form of nonlinear dispersion equations for various nonlinear waveguide structures with Kerr-type films. By using the relation of the interface electric fields, we obtain the generalized form of nonlinear dispersion equations as an analytic form. The “generalized” means that the equation can represent most of nonlinear waveguide structures with up to five linear and/or nonlinear layers. For example, we apply the generalized dispersion equation to 4-types of nonlinear waveguide structures: I)the waveguides with a nonlinear core layer, II)the waveguides with two nonlinear core layers, III)the planar structures having a linear core with nonlinear surrounding media, and IV)the five-layer nonlinear waveguides having symmetric or asymmetric structures.
Coupled near field and radiation field interactions and coherent states in microcrystals
Authors: Fork R. L. , Jones M. W. , Dimmock J. O.
Published: February 2023

Coherent states in microcrystals are important as potential means for approaching the fundamental limits on speed and efficiency in optical switching. Workers are only now beginning to master means of preparing these coherent states at excitation levels of one or a few quanta. We have identified a mechanism that could explain some aspects of coherent state preparation in microcrystals having optical wavelength dimensions. Realization of this mechanism requires no unusual properties, other than satisfying certain precise dimensional requirements on the microcrystal, means of exciting the state, and a constraint on dephasing rates. Many real systems can satisfy these constraints.
Giant Kerr-type nonlinearities using electromagnetically induced transparency (EIT)
Authors: Schmidt H. , Imamoglu A.
Published: February 2023

Giant χ3 coefficients for cross-phase modulation are obtained in a scheme using EIT. Conditional phase shifts ≈ π occur at power levels corresponding to less than 1 photon/ns.
A powerful, diffraction-limited semiconductor laser using photorefractive beam coupling
Authors: MacCormack Stuart , Feinberg Jack , O'Brien Steve , Lang Robert J. , Klein Marvin B. , Wechsler Barry A.
Published: February 2023

Semiconductor flared amplifiers now routinely emit ~1 watt of light in a diffraction-limited, single-frequency beam when driven at currents of a few amps.1 However, if driven at higher currents, the output beam breaks into filaments that spread light into higher-order modes.2 Here we present a simple method for extracting a diffraction-limited beam from the highly-filamented output of a semiconductor amplifier. With this method we can now operate the amplifiers at currents 3-4 times their diffraction-limited range and still obtain a diffraction-limited beam. By combining the outputs of multiple amplifiers, this method should produce very high power diffraction-limited beams from semiconductor lasers.
Demonstration of 3-D Image Reconstruction Using a Photorefractive Storage Media
Authors: Anderson Richard J. , Ketchel Brian P. , Wood Gary L. , Salamo Gregory J.
Published: February 2023

Photorefractive crystals have been used for a long time for holographic storage of two dimensional (2-D) images. In this paper we report the use of strontium barium niobate (SBN) crystal to store and project three dimensional (3-D) images.
Self-Compensating Laser-Based Ultrasound Sensors Using Photo-Induced EMF Detection
Authors: Pepper D.M. , Dunning G.J. , Mitchell P.V. , Klein M.B. , O’Meara T.R.
Published: February 2023

Laser ultrasonics [1] offers a technique for nondestructive, noncontact ultrasonic inspection, with the potential for in-factory closed-loop control and quality assurance of the manufacturing process. Progress has been made [1,2,3] which may enable this novel diagnostic to find its way into the manufacturing arena. However, the technology has yet to be cost-effective for most industrial end-users. In particular, the need to compensate for workpiece vibrations, relative platform motion, and optical distortions has driven up the system cost, including active stabilization and costly optics. Compensation techniques including optical phase conjugation [4,5], double-pumped phase conjugation [6,7,8], and two-wave mixing [9,10,11] can potentially enhance the performance of laser ultrasonic diagnostics. These schemes enable wavefront-matching of the beams for efficient coherent detection. However, in some cases, expensive electronic post-processing is required to track out residual mechanical vibrations.
Study of Thermal Nonlinear Refraction in the Transient Regime
Authors: BROCHARD Pascale , GROLIER Valérie , CABANEL Régis
Published: February 2023

Development of passive optical limiters for eye and sensor protection has led to the search for mechanisms that involve large optical nonlinearities in organic materials. Photo-induced thermal effects appear to be a major mechanism in defocusing optical limiters, based on nonlinear refraction[1][2]. Until now, their efficiency has been demonstrated in the quasi steady-state regime, when pulse duration is larger than the thermal lens build-up time. In this paper, we demonstrate the influence of experimental parameters and material physical properties on the efficiency of thermal nonlinear effects in the nanosecond regime.
Electrostrictive Intensity-Dependent Refractive Index of Silica Fibers
Authors: Buckland Eric L. , Boyd Robert W.
Published: February 2023

Generally, it has been assumed that the non-resonant electronic response is the origin of the intensity-dependent refractive index in silica fibers. However, electrostriction has recently been shown to be the source of long range soliton interactions1 through a time-dependent refractive index change. Additionally, recent experimental work has identified a discrepancy between cw cross-phase-modulation (XPM) measurements of the nonlinear refractive index and measurements made using self-phase-modulation (SPM) of 100 ps modelocked pulses2. In the present work we identify electrostriction as the origin of this discrepancy and demonstrate that electrostriction makes a significant time-dependent contribution to nonlinear refraction in optical fibers.
Nonlinear Liquid Crystal Optical Fiber Array
Authors: Khoo I. C. , Lee M. , Wang K. , Wood M. , Guenther B. D.
Published: February 2023

Liquid crystals [LCs] in their various ordered and disordered phases have been shown to possess large optical and electro-optical nonlinearities over wide temporal [cw to picosecond] and spectral [visible to infrared] ranges [1]. Because of their unique physical properties, various novel liquid crystalline structures, such as thin films or pixels with, slab waveguides, LC cored fibers and fiber arrays, could be constructed that will provide superior performance in specific optical switching, imaging and processing applications. In particular, we have previously reported observation of low-threshold stimulated backscattering and optical limiting effects in an isotropic liquid crystal [ILC] cored fibers of centimeters in length [2].
Ultrashort Pulse Second-Order Frequency Resolved Optical Gating with Thin Poled Nonlinear Polymers
Authors: Taft G. , Murnane M. M. , Kapteyn H. C. , Yankelevich D.R. , Knoesen A. , Twieg R. J.
Published: February 2023

Frequency Resolved Optical Gating (FROG) [1] is a newly-developed technique for determining both the amplitude and phase of an ultrashort pulse.[2] Although there are several variations of the FROG technique which use different nonlinear processes, second harmonic generation (SHG) FROG is particularly well suited for measuring un-amplified nJ pulses directly from a modelocked Ti:sapphire oscillator, since SHG produces a much larger signal than the higher order nonlinear processes. In order for SHG FROG to accurately characterize ultrashort pulses, care must be taken to insure the second harmonic signal is not distorted by the nonlinear material, in phase-matched frequency doubling crystals for example, the group velocity mismatch (GVM) can cause severe distortion of the generated pulses over long interaction lengths. Since this finite phase matching bandwidth becomes less of a problem as the crystal thickness is reduced, the thinnest possible crystals (≈ 50 μm) are generally used for ultrashort-pulse measurement applications.[3] However, even using such short crystals, the crystal has to be optimally oriented to achieve proper phasematching for a given center frequency. Furthermore, fabricating such phasematched, polished, ultra-thin crystals is extremely difficult. Thus, an ideal SHG material for short pulse diagnostics is one that can generate an adequate signal intensity while being thin enough to avoid pulse broadening and precise angle tuning.
Nonlinear Optical Effects in the Bulk and at the Surface of Acentric Liquids Demonstrating Natural Optical Activity
Authors: Koroteev N.I. , Makarov V.A. , Shkurinov A.P. , Pakulev A.V. , Angelutc A.A. , Resniansky A.Yu. , Balakin A.V.
Published: February 2023

Recent experimental results and theoretical investigations are reported concerning sum- and difference frequency generation in the bulk of acentric optically - active liquids comprised of chiral molecules (chiral liquids) as well as SHG and THG of femtosecond pulses reflected from the surface of such liquids. Frequency dependence of second-order optical nonlinearity was studied, for the first time. Dramatic resonant enhancement (more than two orders of magnitude) of multiple - wave mixing processes due to excitation of surface electromagnetic waves at the metallic diffraction gratings are also detected and theoretically explained. Several novel nonlinear optical effects are investigated which are characteristic for the acentric isotropic liquids and solids with natural optical activity, including magnetic field induced SHG, optical rectification, photo-galvanic and photo-refractive effects, BioCARS process.
Annealed proton exchange domain inversion erasure in electric-field poled LiNbO3
Authors: Elhadi K. , Sundheimer M. , Baldi P. , Aschieri P. , DeMicheli M. , Ostrowsky D.B. , Webjörn J.
Published: February 2023

The Quasi-Phase-Matching technique (QPM) [1], in which the
ferroelectric domains of a nonlinear material are periodically
inverted in order to compensate for dispersion, has become widely used
for a number of nonlinear processes [2,3,4]. While bulk experiments in
such structures have yielded results close to theoretical predictions,
waveguided versions, which offer additional possibilities (higher
theoretical efficiencies, electrooptic tuning, etc.) have not attained
the predicted efficiencies. In this paper we compare the parametric
fluorescence efficiency in both bulk and Annealed Proton Exchange
(APE) waveguide configurations in an electric-field poled
LiNbO3 sample, in which the inverted domains exist
throughout the entire sample thickness.The results indicate, that even
after annealing, the proton exchange process appears to erase the
periodic domain inversion, to a depth comparable to that of the
exchanged structure, leading to a lack of QPM in that region. Such an
effect had already been proposed by Webjorn [5] concerning domains
inverted by Ti diffusion at the surface of LiNbO3. He also
noted however, that if an inverted "seed" remained below the surface,
annealing could permit regrowth of the inverted structure above the
seed. This model would have led one to expect that in materials poled
throughout their entire thickness, as in E-field poled
LiNbO3, the seed would always be present allowing
appropriate regrowth of the domains during annealing. However, we
shall demonstrate that this does not appear to be the case.
Electric Field Thermopoling of High Dipole Guests when Considered as Ellipsoids
Authors: Cross G.H. , Healy D.
Published: February 2023

It has become common practice to neglect both the molecule's shape and the features of its polarisability anisotropy when applying local field correction factors to studies of the nonlinear optics of dissolved chromophores.
Electro-Optic Coefficients of Thin Layers of BaTiO3
Authors: Niesten M.J.H. , Pulsford N.J , Cillessen J.F.M.
Published: February 2023

Integrated optics require electro-optic materials with high non-linear coefficients. Oxidic materials have strong electro-optic coefficients and do not deteriorate under high process temperatures or due to aging as e.g. polymers do. Much attention has been paid to the growth of oxidic layers for ferroelectric applications as solid state memories. Layers have been grown by radio frequent sputtering [1], metalorganic vapour deposition [2] and pulsed laser deposition [3]. Some layers have been characterized electro-optically by measuring the birefringence [4] and the effective electro-optic coefficient rc has been determined from such measurements [5]. In this contribution we present the electro-optic coefficients r13 and r33 of a layer of BaTiO3 that we measured with ellipsometry.
High Value of χ(3) in Fluorine-Phosphate Glass Doped with CdSxSe1-x
Authors: Vaynberg B. , Matusovsky M. , Rosenbluh M. , Lipovskii A.
Published: February 2023

The non-linear optical properties of semiconductor-doped glass with high semiconductor concentration has been investigated and compared to the optical properties of commercially available color filters(1, 2). We measured the third order nonlinear susceptibility of this new material by observing four wave mixing. We also identify and measure in this glass the onset of competing higher order nonlinear processes, such as six wave mixing. The optical characteristics of all the semiconductor doped glasses are determined by the microcrystals embedded in the glass matrix. The linear and non-linear optical constants of the material can thus be controlled by the proper choice and concentration of the semiconductor dopants, and the size of the microcrystals. Therefore the synthesis of glasses with high concentration of semiconductor microcrystals is important, since this is expected to produce higher optical nonlinearities. The semiconductor concentration is limited by its solubility in the glass. By using a fluorine-phosphate glass matrix(3) we were able to increase this concentration over that of silicate glass color filters, by more than an order of magnitude.
Waveguide-Mode Intersubband Second-Harmonic Generation with Separate Active and Phase-Matching Regions
Authors: Vurgaftman I. , Meyer J. R. , Ram-Mohan L. R.
Published: February 2023

We have performed an analysis of the conversion efficiency for waveguide-mode second-harmonic generation (SHG) with detuned intersubband transitions in asymmetric double quantum wells (ADQW). The modeling includes the effects of absorption, saturation of the absorption and SHG, pump depletion, carrier heating, mode confinement, and the loss of phase coherence due to waveguide, bulk and resonant intersubband contributions to the mismatch of the refractive indices at the pump and second-harmonic frequencies. ADQW designs with the optimum detuning of intersubband transition energies from resonance with the pump and second-harmonic photon energies have been derived from a balance between low absorption losses, sufficient nonlinear susceptibility, and adequate compensation of the refractive index mismatch to maintain phase coherence. These have been determined for structures employing the GaAs/AlGaAs, InGaAs/InAlAs and GaSb/InGaSb/AlGaSb material systems, all subject to the constraint that the epitaxial growth thickness should not exceed 10 μm. In the best GaAs/AlGaAs ADQWs, the maximum attainable conversion efficiency at high intensities is limited by the electron transfer to X-valley states whenever the Γ-valley offsets are large enough to permit optimal detuning. Since GaAs-based waveguides also require a thick bottom cladding to isolate the active region from the substrate, the large waveguide dispersion limits the peak conversion efficiency to 2.6%.
Optimization of Rhodium-Doped BaTiO3 for High-Power Photorefractive Applications in the Near Infrared
Authors: Wechsler B.A. , Bacher G.D. , Nelson C.C. , Klein M.B. , MacCormack S. , Feinberg J.
Published: February 2023

Phase conjugation and two-wave mixing in photorefractive crystals are used for frequency locking, power combining and beam cleanup of laser diodes. One requirement for these processes is a high gain or coupling coefficient, which implies a high trap density. For use at high power levels, another important requirement is low absorption, to minimize insertion loss and heating of the crystal. In order to increase the trap density, researchers have doped crystals to higher and higher concentrations.1,2 Unfortunately, this almost always leads to an undesirable increase in absorption coefficient. In this presentation we describe the use of Rh doping3,4 followed by post-growth annealing to produce BaTiO3 crystals with both high trap density and low absorption at 860 nm.
Nonlinear Optics of Semiconductor Microcavities
Authors: Gibbs Hyatt M. , Lyngnes Ove , Berger Jill D. , Prineas John , Park Sahnggi , Khitrova Galina
Published: February 2023

When the cavity mode of a high-finesse semiconductor microcavity is tuned toward a sharp quantum-well exciton absorption line, the dipole coupling between these two oscillators results in a normal-mode coupling (NMC) anticrossing curve [1], When the two oscillators have the same frequency there are two transmission peaks (see Fig. 1 inset) and two reflection dips corresponding to two new eigenfrequencies of the coupled system. The nonlinear transmission and reflection of 150-fs modelocked pulses incident on an NMC microcavity are reported.
Coherent Phonons as an Ultrafast Probe of Optical Nonlinearities in Semiconductors
Authors: Kurzn H. , Cho G.C. , Dekorsy T. , Hunsche S. , Bakker H.J.
Published: February 2023

Since the first time-resolved observation of coherent phonons in semiconductors [1], the excitation of coherent lattice vibrations in solid states has attracted considerable interest due to the information, which can be obtained from these kind of experiments not accessible by other experimental techniques. We discuss two recent achievements on the observation of the nonlinear dynamics of the coupled phonon-carrier system by pump-probe reflectivity spectroscopy using femtosecond laser pulses.
Nonlinear Optical Susceptibilities; Beyond the Local Field Approximation
Authors: Mukamel Shaul , Knoester Jasper
Published: February 2023

The Bloch-Maxwell equations are usually derived for isolated molecules interacting with an external electromagnetic field. This is justified in the limit of low molecular density, where intermolecular forces may be neglected. The problem which we address in this work is how to extend these equations in a systematic way to incorporate properly intermolecular forces. We thus develop a systematic microscopic basis for the calculation of nonlinear response functions and susceptibilities. Such a theory is essential for relating microscopic, single-molecule, polarizabilities to the macroscopic susceptibilities of optical materials. The local field approximation [1,2] is a mean-field procedure which is widely used in the calculation of molecular susceptibilities at finite densities, when intermolecular forces are important. The local field model provides a simple way to relate the polarizabilities of isolated molecules to the macroscopic susceptibilities. It is clear, however, that this procedure is not rigorous. It fails to take properly into account the correlated dynamics of the interacting many-body system, i.e., correlations among the molecules, as well as correlations between the molecules and the radiation field. Short-range forces (e.g., exchange) are totally neglected in this procedure. Moreover, even the dipoledipole forces are not fully taken into account. The resulting susceptibilities do not depend at all on the wavevectors (apart from the local field contribution) but just on the frequencies. This indicates that processes such as exciton migration and energy transfer and transport (e.g., the Forster transfer) are neglected in this procedure. Such processes are often added phenomelogically in order to interpret transient grating spectroscopy[3], which is a four-wave mixing technique that measures transport processes by following the wavevector dependence of the susceptibilities. The common derivation of the local field approximation cannot be extended to include these processes, since it is intrinsically a mean-field single molecule theory.
Nonlinear Optical Processes in Lower Dimensional Conjugated Structures
Authors: Wu J. W. , Norwood R. A. , Heflin J. R. , Wong K. Y. , Zamani-Khamiri O. , Garito A. F.
Published: February 2023

Strong correlation between π-electrons in effectively reduced spatial dimensions[1] is a guiding concept in designing organic materials possessing large nonlinear optical responses. Microscopic descriptions of second βijk(-ω3;ω1,ω2) and third γijkl(-ω4;ω1,ω2,ω3) order π-electron virtual excitation processes are required in order to understand at a fundamental level the physical properties and behavior of βijk and γijkl and to provide guidelines for molecular designs of new material structures. The purpose of this paper is to report recent developments concerning the origin and mechanisms for γijkl of quasi-1D conjugated structures and recent observations of optical bistability in quasi-2D structures.
Material Parameters Study in Barium Titanate Using a Laser-induced Grating Spectroscopic Probe Technique
Authors: Ditman L. S.
Published: February 2023

Material parameters, including refractive index modulation depth, space charge field, and trap charge density, in photorefractive barium titanate are determined using a novel laser-induced grating spectroscopic probe technique. In this method, shown in Fig. 1, coherent laser beams (grating writing beams) intersect inside the crystal and induce (write) a refractive index grating via the photorefractive effect. A laser probe beam is applied to the crystal parallel to the grating planes (i.e. at normal incidence to the plane of the grating writing beams, in a Raman-Nath type configuration) and is diffracted into higher order modes (|m|≥1) located symetrically at angles ±θDm about the undiffracted (m=0) mode. The crystal is in air and is supported by an optical flat attached to a rotating platform (not shown in Fig. 1) which allows us to rotate the crystal about the z-axis, thus varying the intersection angle of the grating writing beams in the crystal (for fixed writing beams in air), thereby varying the grating spacing, Λg, in the crystal. Additionally, the platform provides for tilt adjustment of the x-y plane in order to precisely align the induced phase grating planes and the probe beam to obtain symmetry in the intensities of the positive and negative modes (orders) of diffraction.
Picosecond Photorefractive and Free-Carrier Nonlinearities in Semiconductors
Authors: Smirl Arthur L. , Dubard J. , Valley George C. , Boggess Thomas F.
Published: February 2023

A variety of picosecond time-resolved two-beam coupling, transient grating and degenerate-four-wave mixing techniques are used to investigate the nonlinear loss and to measure the strength, formation and decay of photorefractive gratings written in GaAs and InP:Fe and of free-carrier gratings written in Si, GaAs, and InP by 43-ps pulses at a wavelength of 1 μm. We present data and numerical calculations as a function of fluence, time delay, pump-to-probe ratio, pump polarization, analyzer angle and crystal orientation. We observe photorefractive gains of a few percent at fluences of a few pJ/μm2 (0.1 mJ/cm2) in GaAs and InP, and we identify two sources for the photorefractive space-charge field. It is principally between mobile free carriers and stationary single-photon ionized donors at low fluences and between mobile electrons and holes produced by two-photon absorption at high fluences. We also observe strong transient energy transfer from the nominally "unshifted" free-carrier index gratings written in GaAs and InP by two-photon absorption and in Si by single-photon indirect absorption. We have demonstrated optical switches based on the pump-induced photorefractive rotation of the probe polarization in GaAs with on/off ratios of >2/1 at fluences as low as 400 fJ/μm2 and optical switches based on free-carrier transient-energy-transfer with on/off ratios >20,000/1 at 200 pJ/μm2. We have also used transient-energy-transfer to construct weak beam amplifiers with gains >25 at 30 mJ/cm2. Finally, these techniques have been used to obtain information about the properties of the deep-level (mid-gap) states in GaAs (EL2/EL2+) and InP (Fe2+/Fe3+), such as the cross sections and number densities.
Darkening and clearing and light by light modulation in semiconductor-doped glass
Authors: Ruddock I.S. , Illingworth R. , Zheludev N.I.
Published: February 2023

Semiconductor-doped glasses (SDGs), consisting of small (~100Å) inclusions of CdSxSel-x in silicate glass and commercially available as sharp cut-off filters, are the subject of intensive investigation. They are materials with large effective third order susceptibilities at wavelengths near the band-edge and are suitable for optical phase conjugation and four wave mixing [1]. Data on their nonlinear optical properties and relaxation parameters have previously been obtained by means of pulsed nano-, pico- and femto-second lasers [2,3,4]. For this reason relatively slow optical nonlinearities of SDGs and their dynamics have not been examined. This paper presents the results of an experimental study of a SDG light by light modulator using a pump-probe technique. Laser induced darkening and clearing with a millisecond relaxation time have been observed and are shown to lead to complex structure in the subharmonic band of the modulation frequency and a near chaotic response. These processes and their interaction must be understood before SDGs can be used in optoelectronic devices.