bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and Epitaxy of Materials for Multilayer X-ray Optics
Authors: Slaughter Jon M. , Kearney Patrick A. , Ruffner Judith A. , Falco Charles M.
Published: February 2023

New material pairs are needed to provide useful mirrors at wavelengths where currently none exist, and to improve on performance at wavelengths where there are existing mirrors. In this paper we discuss our studies of selected new materials. Our studies take a surface analysis approach toward characterizing reactions at interfaces, the sharpness of interfaces, and the effect of the thin film growth mode on roughness. The studies were carried out in molecular beam epitaxy systems for two reasons: to study epitaxial growth of promising materials as a step toward single-crystal multilayer mirrors, and to exploit the powerful analytical tools available for surface analysis in a UHV environment. Growth of Be-, and B-based materials pairs have been studied with a wide variety of techniques including Auger, XPS, RHEED, LEED, and STM with the goal of determining interface structure, overlayer morphology, and crystal structure.
Multilayer X-Ray Mirror Absolute reflectivity, Energy Band Pass and Overlapping Order Determination Using an X-Ray tube and a SI(LI) Detector
Authors: Dhez P. , Duval H. , Malaurent J.C.
Published: February 2023

X-ray interference mirrors are a particular case of artificial multilayered media for which the wanted property is a high intensity of the diffraction phenomena itself. For such applications one needs to know the performance of the mirrors at different wavelengths. We would like to demonstrate here how such X-ray reflectivity tests can be achieved on a laboratory apparatus to get absolute reflectivity and without the need of a synchrotron source.
A Soft X-ray and Extreme U.V. Reflectometer Using a Laser Produced Plasma Source and a High Throughput Monochromator
Authors: Gullikson E. M. , Underwood J. H. , Batson P. C. , Nikitin V.
Published: February 2023

Measurements in the soft x-ray and extreme ultaraviolet regions of the spectrum have historically been hampered by the lack of a bright, tunable source. Although synchrotron radiation sources are gradually filling this need, such facilities are not sufficiently compact and inexpensive to be within the reach of an average laboratory. The commercial availability of compact, inexpensive pulsed lasers has changed this picture. The high temperature plasma produced when the light from such a laser is focused upon a suitable metal or dielectric target emits x-rays and extreme ultraviolet radiation that can either be a rich line spectrum or a smooth and intense continuum, depending upon the target material. Such a source needs only monochromatization to make it useful for a wide variety of measurements and calibrations.
Preliminary Survey of Material Pairs for XUV Multilayer Mirrors for Wavelengths Below 130 Å
Authors: Montcalm Claude , Kearneyt P. A. , Slaughtert J. M. , Chaker M. , Falco Charles M.
Published: February 2023

Remarkable progress, within limited wavelength ranges, has been made in the field of normal incidence XUV mirrors. High performance Mo/Si multilayer mirrors exist for wavelengths between 125 and ~250 Å, and reflectivities greater than 60% have been achieved around 130-140 Å.1-4 Good results were also obtained with C and B4C-based multilayer mirrors at wavelengths just above the C and the B K-absorption edges at 44 Å and 67 Å, respectively.5-7 However, there are wavelength regions such as the water window or just below the Si L-edge, where none of the well-established material pairs can achieve reflectivities adequate for many applications. The search for new material pairs to bridge these wavelength gaps has motivated the work that is briefly discussed here.
Roughness Correlations in Si/Mo Multilayers
Authors: Slaughter J. M. , Stearns G. D. , Falco Charles M.
Published: February 2023

Low-angle x-ray diffraction with hard x-rays is a standard technique for characterization of interface quality in multilayers. Although the specular reflectivity, measured by a θ-2θ scan, is very sensitive to interface roughness, it reveals little about the nature of the roughness. Fortunately, more information can be obtained from an analysis of the non-specular scattering of the x-rays. The theory of non-specular scattering of x-rays from multilayers only recently has been developed to a level which allows for comparison with experiment.1,2,3,4,5 A key feature of non-specular scattering from multilayers, explained clearly in reference 3, is that correlated roughness should give rise to resonant scattering in particular non-specular directions. Such a resonant intensity has been observed experimentally.2,6,7,8 It is clear from the theories referenced above that correlated roughness can account for the non-specular features we and others have observed. Having an appropriate theory now gives us the possibility to use non-specular measurements to compliment the standard specular characterization techniques.
Development and use of soft-x-ray multilayer polarizing elements
Authors: Yamamoto Masaki , Kimura Hiroaki , Mayama Kou , Furudate Minaji , Yanagihara Mihiro
Published: February 2023

Soft-x-ray multilayer mirrors are well demonstrated with respect to their high reflectance at near normal incidence. Such multilayer mirrors can be used at other incidence angles off normal though the peak wavelength moves to shorter side as the angle of incidence increase. When we use a mirror at off-normal incidence, polarization dependence appears in the reflectance since p-reflectance generally differs from s-reflectance and decreases rapidly as the angle comes close to the pseudo Brewster angle at which p-reflectance takes minimum. In the soft-x-ray region, the complex refractive indices of material are very close to 1, which indicates the pseudo Brewster angles of multilayer mirrors are around 45°.
High resolution X-ray scatter studies from single films and multilayers
Authors: Christensen F. E. , Homstrup A. , Joensen K. D. , Abdali S. , Høghøj Peter , Joensen K. D. , Slane P. , Romaine S. E.
Published: February 2023

Metal coatings such as Au1 and Ir2 will be used as the reflecting surface in current X-ray telescope programs. Likewise, multilayers have been used3 in normal incidence soft X-ray telescopes and are suggested for future grazing incidence telescope projects both near 6-7 keV and in the hard X-ray regime4 (10-100 keV). The accurate evaluation of the imaging behaviour of telescopes based on these structures requires characterizing the surface/interface structure on lengthscales from Ångstrøms to mm's. In this paper we present high resolution X-ray scattering data from such surfaces obtained at Cu-Kα1 (8.048 keV), Fe-Kα1 (6.404 keV) and Al-Kα (1.487 keV). We demonstrate that the combination of low, high and ultrahigh resolution scatter measurements can be performed which is capable of detecting scattering from roughness over lenghtscales from a few thousand Å to ~10 mm. The sensitivity of these measurements allow one to detect scattering from roughness having r.m.s. roughness values as small as a few Å in the entire lenghtscale range listed above. The diffuse intensity is mapped completely in reciprocal space for the multilayer structures and the influence of the resolution function is accurately evaluated. The data have been analyzed using the most recent theoretical expressions for the diffuse X-ray scatter from single films and multilayers5.
X-Ray Ellipsometry: A Surface Sensitive Technique to Characterize Thin Films and Layered Materials
Authors: Ziegler E. , Doublet D.
Published: February 2023

As polarization sensitive experiments are an important trend in x-ray physics nowadays, a strong demand has arised for producing various polarization states and for measuring them, therefore, calling for polarizers for the x-ray domain. Intense x-ray sources exist or are under development; such as the ones produced by a laser plasma or by synchrotron radiation. In the latter case, the radiation is essentially linearly polarized on axis with an electric field parallel to the plane of the electron. If another state of polarization is desirable one can use either quarter and half wave plates[1] or exotic insertion devices, such as a crossed undulator[2], a planar/ helical undulator,[3] or an asymmetric wiggler. It is always important to know the amount of unpolarized light that is present. Quarter and half wave plates can be made of perfect crystals[4] and have effectively been used at energies higher than 7 keV[5]. In the soft x-ray region the property of phase retardation between s and p components were recently proven for multilayers both in the reflection[7,8] and the transmission[6][10] geometries. However, an upper energy limit of application seems to be about 400 eV when accounting for the minimum d-spacing that can be produced at present without sacrifying the multilayer performance. Other authors[7] have mentioned the carbon K-edge as an upper limit because of an increase in the absorption contribution.
Multilayered Diffractive Optics for X-Ray Focusing: Experimental results (1-10 keV) and theoretical predictions using dynamical theory.
Authors: Chevailier P. , Dhez P. , Erko A. , Ifdir M. , Legrand F. , Mirone A. , Soulli G.
Published: February 2023

We present results obtained on 1D and 2D X-ray focusing optics based on lamellar gratings prepared by ion etching of flat multilayers.
Low Light Level CCD Imaging in Astronomy
Authors: Tyson J. Anthony
Published: February 2023

Much of modern optical and IR astronomy is "photon starved". That is, to pursue current research in imaging and spectroscopy it is often necessary to integrate longer than several nights, for sufficient signal-to-noise ratio. Yet for such long integrations there are diminishing returns: low-level systematic error due to "weather" (night sky variations, clouds, etc.) limit the accuracy of photometry. Thus, this fractional error in night sky brightness translates into a limiting faintness for surface photometry of galaxies. Even worse, there are limiting upper-atmosphere generated systematics on the detector itself. The solution is to use the highest quantum efficiency detectors on the largest telescopes, and develop image acquisition and reduction techniques which cancel the systematics.
Pupil Plane versus Image Plane in Michelson Stellar Interferometry
Authors: Roddier Francois
Published: February 2023

Following Michelson [1] original experiment, the beams from a stellar interferometer are generally combined in the image plane [2]. Interference fringes are observed when the images produced by each aperture are superimposed. The fringe spacing is set by the apparent angular distance between the apertures as seen from the image. It can be set to any value and is insensitive to image motion or guiding errors. A Fourier analysis of the image gives the energy at the fringe spatial frequency as an estimate for the square of the fringe visibility, filtering out the noise at all other spatial frequencies [3,4]. A drawback of this design is that the images do not always exactly coincide due to turbulence induced image motion or guiding errors thus randomly reducing the apparent fringe visibility and therefore decreasing the signal-to-noise ratio.
Fundamental Statistical Limitations to X-Ray Quantum Detection
Authors: Shaw Rodney , Rabbani Majid
Published: February 2023

A model for the detective quantum efficiency (DQE) of a screen-film system has recently been developed1,2 which includes all the principle inefficiencies of both screen and film. Subsequent comparison of this model with detailed practical measurements has confirmed its power of prediction.3
Strip Beam Digital Radiography Using a Kinestatic Charge Detector
Authors: DiBianca F. A. , Wagenaar D. J. , Fetter J. E. , Tenney C. R. , Bolz M. J. , Vance J. E. , McDaniel D. L. , Granfors P.
Published: February 2023

The past decade has seen a marked increase in research on digital electronic detectors for x-radiographic imaging systems. This paper summarizes recent work on scanning strip detectors with emphasis on a new technique known as kinestatic charge detection (KCD). Principles of operation, theory and early experimental results are presented.
The Use of Optical Dead-Time Effects for the Generation of Anti-Bunched and Sub-Poissonian Photo-Electron Statistics
Authors: Jakeman E
Published: February 2023

A great deal of effort has been devoted during the last decade to the theory of nonclassical states of the radiation field. From a practical point of view some of the most interesting predictions of these theories concern the generation of light with sub-Poissonian photon counting statistics for which Such light is evidently less noisy than laser radiation with obvious implications for the improved performance of optical systems. When the temporal autocorrelation function of the photon counts increases as the delay time increases from zero the light is also said to be antibunched.
Restoration of Photon-Limited Images
Authors: Frieden B. Roy
Published: February 2023

Modern image detectors have attained the ultimate in sensitivity, enabling single-photon events to be seen. An array of such detectors may be used to form a "photon count" image, such as on the left in Fig. 1. If such a photo also suffers from blur, how well can it be restored to the ideal object on the right? We shall take a Bayesian1 view and seek the maximum probable (m.a.p.) and mean probable (m.m.s.e.) estimates of the object. This approach marries the known physics of photon image formation to estimation theory, a match which the Rev. Thomas Bayes himself might have blessed. As will be seen, it allows ultimate questions to be asked on object structure, even in cases of severe photon depletion.
Sub-Shot Noise Interferometry and Quantum Imaging
Authors: Slusher R. E. , La Porta A. , Grangier P. , Stepnoski R. , Kleinfeld D.
Published: February 2023

Optimizing the sensitivity for interferometric measurement of optical phase involves maximizing the intensity of the illuminating light source and minimizing any noise sources. Limits to the light source intensity may arise from the availability of a stable high-power laser or from damage to the system being measured. For example, we describe here a scanning confocal polarization microscope designed to image the dynamics of nerve networks. In this case the light intensity limit is set by several factors, including the scanning rate, the required response time and damage limits of the biological system. Assuming a stable experimental configuration for the interferometer and light source, the limiting noise source for visible light interferometry is shot-noise associated with the quantum state of the light inputs to the interferometer. Shot-noise can be thought of as arising from vacuum fluctuations entering the dark input port of the interferometer.(1) These vacuum field fluctuations combine with the light entering the other port to cause shot-noise in the detected photocurrent at the output ports of the interferometer. This shot-noise current normally limits the measured phase variance Δϕ to a value of
1/N where N is the average number of photons detected in a measurement interval. We describe an experiment which demonstrates that this shot-noise limit can be improved by injecting squeezed vacuum into the normally dark input port.(2) In this case the phase variance is reduced below the
1/N limit by the degree of squeezing. In contrast to early experiments,(2) we are now operating the interferometer in a dark fringe mode(3–5) in order to avoid setting a limit to the light level caused by detector saturation (near 1 mW).
Photon-Limited Pattern Recognition
Authors: Morris G. Michael
Published: February 2023

Often input scenes contain a vast amount of information, which tends to make pattern-recognition decisions laborious and time consuming. In traditional digital pattern recognition methods, one digitizes the input scene using a two-dimensional detector, e.g. a solid-state photodiode array and a frame store. If the detector consists of, say, a 1000 x 1000 array of detection elements, then one has to process a million points of data. This is too much information for even very large computers to process in real time, so one generally transforms the input information into some sort of feature-space representation, e.g. through the use of edge-enhanced images, and makes the recognition decision based on this reduced data set.
Deconvolution of turbulence-degraded images from wavefront sensing
Authors: Primot J. , Rousset G. , Marais T. , Fontanella J.C.
Published: February 2023

The angular resolution of ground-based large telescopes is essentially limited by atmospheric turbulence. The optical resolution limit is of the order of one arc-second however large the aperture diameter may be. The turbulent atmosphere induces randome spatial and temporal fluctuations in the wavefront coming from the object and drastically degrades the image.
First Room Temperature CW Operation of GaInAsP/InP Surface Emitting Laser
Authors: Baba T. , Yogo Y. , Suzuki K. , Koyama F. , Iga K.
Published: February 2023

We have achieved the room temperature cw lasing operation in GaInAsP/InP vertical cavity surface emitting laser diodes for the first time. By employing a buried heterostructure with a 1.3 μm range circular active region1 and a thermally conductive MgO/Si heat sink mirror, the cw lasing operation was obtained up to 14 °C, as shown in Fig. 1.
Pros and Cons of Reduced Energy Relaxation at Low Dimensions for Optoelectronics Devices
Authors: Benisty H.
Published: February 2023

Unlike the early recognition of the improved performances of quantum
wells in optoelectronic devices, there is still no clear demonstration
of similar gains from quantum wires, as one would expect from this
further step in the spectral concentration of the oscillator strength.
It is even far worse for quantum boxes where a universal collapse of
the photoluminescence (PL) yield is observed for lateral sizes below
~100 nm, i.e. for quantization energies way below the ~20 meV required
for improved room-temperature operation.
Threshold Reduction of 1.3 μm GaInAsP/InP Surface Emitting Laser by a Maskless Circular Planar Buried Heterostructure Regrowth
Authors: Baba T. , Suzuki K. , Yogo Y. , Iga K. , Koyama F.
Published: February 2023

By a maskless PBH (planar buried heterostructure) LPE regrowth technique, we improved the hetero-interface of GaInAsP/InP circular BH structure. In this report, we demonstrate a low threshold 1.3 μm BH type surface emitting laser using this technique. We call this type of device circular PBH surface emitting laser (CPBH-SELD).
Pixels Consisting of a Single Vertical-Cavity Laser-Thyristor and a Double Vertical-Cavity Phototransistor
Authors: Kosaka Hideo , Ogura Ichiro , Saito Hideaki , Sugimoto Mitsunori , Kurihara Kaori , Numai Takahiro , Kasahara Kenichi
Published: February 2023

Bi-directionally cascadable optical pixels comprising low-threshold (1mA) high-efficiency (0.25W/A) surface-emitting laser-thyristors and wide-bandwidth (50Å) high-photocurrent-gain (230A/W) double vertical-cavity phototransistors are described.
Intensity Modulation Bandwidth Limitations of Vertical-Cavity Surface-Emitting Laser Diodes
Authors: Peters M.G. , Majewski M.L. , Coldren L.A.
Published: February 2023

Vertical-Cavity Surface-Emitting Lasers (VCSELs) are seen as major candidates for optical interconnections. This is due to their extremely low threshold currents, easy on-chip integration of multiple devices, and high-efficiency fiber coupling. Important to most practical applications of VCSELs is the ability to operate these devices at high data rates (up to several Gbit/sec) which requires their intensity modulation bandwidths to be in the GHz frequency range.
High Contrast, All-Optical GaAlInAs/AlInAs Multiple Quantum Well Reflection Modulator at 1.3 μm
Authors: Krol M.F. , Boncek R.K. , Ohtsuki T. , Khitrova G. , McGinnis B.P. , Gibbs H.M. , Peyghambarian N.
Published: February 2023

Recently, there has been considerable research interest in multiple quantum well (MQW) light modulators which utilize reflective nonlinear asymmetric Fabry-Perot etalons to achieve extremely high contrast ratios with both electrical and optical control.1-3 Here, we demonstrate the first all-optical, high-contrast GaAlInAs MQW asymmetric reflection modulator for operation at 1.3 μm.
Time Resolved Optical Orientation Used to Examine Coulomb Screening and Phase Space Filling in Quantum Well Excitonic Saturation
Authors: Snelling M. J. , Perozzo P. , Bambha R. , Miller A. , Hutchings D. C.
Published: February 2023

Picosecond pulses from a mode locked dye laser were used in an
excite-probe configuration (figure 1) with excite and probe beam
powers of 200uW and 20uW respectively. Both beams were polarised to
produce either mutually orthogonal linear polarisations
(linear-linear), the same circular polarisation (same-circular), or
opposite circular polarisation (opposite-circular). The sample was
fabricated by MBE with a p-type background doping of
1016cm-3, etched to remove the GaAs substrate,
and consisted of 120 periods of 65Å quantum wells with
212Å AI0.4Ga0.6As barriers.
Combined Quantum Effects for Electron- and Photon-Systems in Semiconductor Microcavities
Authors: Yamanishi Masamichi , Lee Yong
Published: February 2023

One of most important conclusions in cavity-quantum-electrodynamics is that spontaneous emission of an atom can be controlled by squeezing zero-point fluctuations of the photon fields surrounding the atom in both spatial and frequency domains1). As for quantum optoelectronic device application, in addition to quantum control of photon system, it is of great important to dynamically control electron system as well in order to alter spontaneous emissions. This can be easily realized in semiconductor systems by a combined use of distributed Bragg reflectors (DBRs) and the quantum confined Stark effect (QCSE) for control of photon and electron systems, respectively. The main purpose of this talk is to demonstrate our experimental results on physical phenomena originating from quantum control of electron-and photon-systems2)3), and its implications for device-applications4) involving the possibility of a novel scheme for the generation of photon-number squeezed state5).
Controlled Atomic-like Spontaneous Emission from Implanted Erbium in a Si/SiO2 Microcavity
Authors: Vredenberg A.M. , Hunt N.E.J. , Schubert E.F. , Jacobson D.C. , Poate J.M. , Zydzik G.J.
Published: February 2023

Since the advent of vertical cavity surface-emitting lasers, a renewed interest has also emerged for the spontaneous emission from Fabry-Pérot microcavities. Changes in spontaneous emission characteristics in a 1D microcavity were predicted long ago,1 but have been demonstrated only recently in the optical domain for solid-state, e.g. semiconductor, structures where changes in spectral purity, lifetime, and emission intensity were observed.2 However, the interpretation of these effects is somewhat obscure, because these structures are highly absorbing and often involve band-to-band, rather than atomic, transitions. In the present study, we use optically transparent Si/SiO2 cavities, consisting of two coplanar Si/SiO2 distributed Bragg reflectors (DBR) around a (λ/2) SiO2 active region, which was doped with ~0.2 at.% Er3+ ions through MeV ion implantation. The Er3+ ions in SiO2 exhibit a sharp, atomic-like, intra-4f transition around λem=1.54 μm, which is effectively shielded by the outerlying filled 5s2 and 5p6 shells. Recently, we reported on the considerable enhancement of the spontaneous emission intensity out of such an Er-doped microcavity.3 In this paper, we present a more detailed study of the modified spontaneous emission, including fluorescence decay measurements to study the effect of the cavity on the spontaneous emission rate.
Threshold Dependence on Cavity Length and Mirror Reflectivity in Fabry-Perot Microcavity Semiconductor Lasers with High Contrast Mirrors
Authors: Huffaker D.L. , Deppe D.G. , Pinzone C.J. , Rogers T.J. , Streetman B.G. , Dupuis R.D.
Published: February 2023

There is currently a great deal of interest in the use of small optical cavities to control the spontaneous emission characteristics from semiconductor light emitting diodes and lasers. Predictions of the magnitude to which the effect may be realized range from novel forms of lasers having "zero-threshold", to skepticism as to whether controlled spontaneous emission may impact practical devices at all since it simply represents "filtering". Therefore, experimental investigations which elucidate the role controlled spontaneous emission may play in present day realizable device structures are needed.
Interleaved-contact electroabsorption modulator using doping-selective electrodes with 25 °C to 95 °C operating range
Authors: Goossen K.W. , Cunningham J.E. , Jan W.Y. , Miller D.A.B.
Published: February 2023

As the number and bandwidth requirements of connections to integrated circuit chips approach thousands and hundreds of megahertz, respectively (which is occurring now), the capability of standard electrical chip input/output becomes strained. For this reason optical input/output to chips is being explored by a number of groups.1 In modulator systems, an off-chip laser would be split into an array of beams that illuminates an array of surface-normal modulators. The modulators would be switched by the on-chip electronics to imprint information on the reflected beams. Multiple quantum well (MQW) modulators are attractive because they can produce large enough absorption changes in surface-normal devices with good yields, low intrinsic power dissipation and apparently good reliability. Since the modulators are p-i-n type devices they are also efficient input detectors. 64x64 arrays of operational modulators have been demonstrated.2 Reliable modulators have also been demonstrated on silicon.3
Functionally All-Optical Bistable p-i-p-i-n Device with Asymmetric GaAs/AlAs Coupled Quantum Well Absorption Layers and an AlAs Resistive Layer
Authors: Tokuda Yasunori , Abe Yuji , Tsukada Noriaki
Published: February 2023

Optical bistabilities have been receiving considerable attention for potential application in future ultra-high performance information processing. Especially an all optical bistable function, which can be achieved at low input power, seems to be very promising.1
Visible Wavelength LEDs and Reflection Modulators with AlGaAs/AlAs Quantum Wells
Authors: Pezeshki B. , Kash J. A. , Liu Daxin , Lord S. M. , Harris J. S.
Published: February 2023

Since most direct gap semiconductors have bandgaps in the infra-red, there is considerable effort in extending the operation of devices into the visible. In this work we show how indirect gap AlGaAs/AlAs quantum wells (QWs) can be suitable for the fabrication of reflection modulators and LEDs. We demonstrate a modulator with a 30% reflectivity change and a room temperature LED.
Optimum Strained MQW Structure in 680 nm AlGaInP Laser Diodes for Low Threshold and High Power
Authors: Tanaka T. , Kawanaka S. , Yanagisawa H. , Yano S. , Minagawa S.
Published: February 2023

It has recently been shown that various important laser characteristics are improved by adopting the strained MQW (SMQW) structure. In the case of visible AlGaInP lasers for use in the optical disk systems, high-power operation of the fundamental transverse-mode is an important requirement. Stable high output around 30 mW has already been attained using compressively strained QWs [1][2]. Compressive strain is introduced by increasing the In content of the GaInP alloy. This brings about a decrease in bandgap energy of the active region, which causes a large potential barrier that confines the injected carriers. In fact, the wavelength red-shift caused by the compressive strain can reduce threshold currents [3].
Optical Properties of Tensile and Compressively Strained (GaIn)P-(AlGaIn)P Multiple Quantum Wells
Authors: Dawson Martin D. , Duggan Geoffrey
Published: February 2023

(AlGaIn)P bulk and quantum well heterostructures, grown on GaAs substrates, are being intensively studied for visible laser diode and LED applications, because of the large room-temperature direct energy gaps (up to ~2.3eV) which they offer. Early effort has concentrated on the lattice-matched Ga0.52In0.48P–(AlyGa1–y)0.52In0.48P system. In this case1, laser action has typically been achieved at -660 to 680nm at room temperature, with threshold current densities of at best 0.2 – 0.4 kA cm−2. These lasers have commonly shown rapid degradation in threshold current density as the temperature is increased above 294K. Recently, in an effort to improve performance and shorten the operating wavelength, laser structures with (GaIn)P quantum well active regions under coherent strain on the GaAs substrate have been produced. Both1 compressively and tensile strained active layer lasers have been investigated, with strain of up to ~1% in each case.
Ultrafast Near-Field Optical Probing
Authors: Stark Jason B. , Mohideen Umar , Slusher Richart E.
Published: February 2023

Direct measurement of carrier dynamics, using femtosecond light sources, has yielded a wealth of understanding within the field of condensed matter physics[1]. Also, recently, near-field optical probe techniques have enabled optical measurements with spatial resolution below the diffraction limit[2]. An understanding of many scientifically and technologically important issues require a knowledge of the local behavior of carriers within materials and microstructures. We report the development of the required instrumentation, and the first measurement of carrier dynamics with spatial resolution below the diffraction limit and temporal resolution below 60 fs.
STOEM: Scanning Tunneling Optoelectronic Microscope
Authors: Takeuchi Koichiro , Mizuhara Akira
Published: February 2023

We applied a scanning tunneling microscope (STM) to optoelectronic sampling measurement of high-speed electrical waveform[1]. An optical pulse train was used to turn on and off a photoconductive semiconductor switch (PCSS) made of low temperature GaAs on the STM probe. This special STM can be called scanning tunneling optoelectronic microscope (STOEM).
High-Frequency On-Wafer Testing with Freely Positionable Silicon-on-Sapphire Photoconductive Probes
Authors: Pfeifer T. , Heiliger H.-M. , Roskos H. G. , Kurz H.
Published: February 2023

Electronic and optoelectronic devices have become available with cut-off frequencies up to several hundreds of GHz. This technological push necessitates the development of new measurement techniques, because conventional electronic measurement equipment such as network analyzers or sampling oscilloscopes are limited in bandwidth to 40 - 100 GHz.
Quantum Cascade Lasers
Authors: Capasso F. , Faist J.
Published: February 2023

The recently demonstrated quantum cascade laser is a fundamentally new semiconductor laser.1-3 It relies on only one type of carrier (unipolar laser) and on quantum jumps of electrons between discrete conduction band energy levels of quantum wells. As such the wavelength can be tailored over a very wide range from the mid-ir (a few microns) to the far-ir (~100 μm) by simply varying layer thicknesses. Two types of quantum cascade lasers will be discussed. In the original structure the relevant intersubband radiative transition is between states centered in different neighboring wells to facilitate population inversion, i.e. the transition is diagonal (Fig. 1). In this design, however, the width of the luminescence transition is relatively broad (FWHM~22 meV) due to the interface roughness since electrons traverse several heterointerfaces in the photon emission process. As a consequence the peak gain is reduced. To circumvent this problem we designed the structure of Fig. 2 where electrons make a vertical radiative transition essentially in the same well. This reduces considerably the width of the gain spectrum (FWHM = 10 meV) and therefore the laser threshold current density. To prevent electron escape in the continuum, which is greatly reduced in the case of the diagonal transition, the superlattice of the digitally graded injector is designed to act as a Bragg reflector for electrons in the higher excited state and to simultaneously ensure swift electron escape from the lower states via a miniband facing the latter (Fig. 2). A crucial feature of both structures is that the lower state of the laser transition is separated by an optical phonon (≈ 30 meV) from the n = 1 state. This strongly enhances the scattering of electrons out of the n = 2 state. The calculated time is τ21 ≃ 0.6 ps which is considerably less than the relaxation time between the n = 3 and n = 2 state (a few ps) thus creating the population inversion condition. Electrons can in turn tunnel out of the n = 1 state in a subpicosecond time to prevent electron build-up.
Scaling of Stark-Shifted Nonhneanties in Multiple Quantum Well Structures
Authors: Cartwright A. N. , Huang X. R. , Smirl Arthur L.
Published: February 2023

Optical switching and logic devices require a large optical nonlinearity (absorptive or refractive) per absorbed photon (or injected charge), combined with a rapid excitation recovery time. The accumulated absorptive (or index) changes during a laser pulse are proportional to the shorter of either the pulse duration or the excitation lifetime. Optimally the two are matched, in which case the switching energy (power-time product) is determined primarily by the change in absorption coefficient (or refractive index) per photogenerated carrier-pair. Any mechanism, material or structure that will enhance the per-carrier nonlinear response is therefore of considerable interest. Device structures (such as self-electrooptic effect devices (SEED’s), hetero n-i-p-i's, and piezoelectric multiple quantum wells (MQWs)) that rely on the screening of applied, built-in or intrinsic fields are purported to have large per carrier nonlinearities primarily because the carriers generated in a single well can escape and move to screen multiple wells. As a class, we refer to the nonlinearities in such structures as Stark-shifted nonlinearities, since they arise from a reduction in the quantum-confined Stark effect (QCSE) as the field is screened by the photogenerated charge.
Dynamic Wannier-Stark Effect and Superradiance Switching in Semiconductor Superlattices
Authors: Khurgin J. B. , Lee S. J. , Lawandy N. M. , Li S.
Published: February 2023

We investigate the possibility of observing the transition between the localized states and the extended states in semiconductor superlattices (SL) in the presence of strong external ac field. i.e., the dynamic Wannier-Stark effect [1] and by switching of superradiance.
Normal Incidence Intersubband Absorption in Vertical Quantum Wells.
Authors: Berger V. , Vermeire G. , Demeester P. , Weisbuch C.
Published: February 2023

For all applications involving intersubband transitions (1, 2) (ISBTs) (like Quantum Well Infrared Photodetectors(3)), the interaction between light and quantum confined electrons yields to the very stringent quantum mechanical selection rule governing intersubband transitions, which stipulates that the electric field is absorbed through its component normal to the direction of confinement. The most important consequence of this selection rule is the impossibility to excite intersubband transitions at normal incidence.
One-dimensional Exciton Diffusion in GaAs Quantum Wires
Authors: Nagamune Y. , Watabe H. , Nishioka M. , Arakawa Y.
Published: February 2023

The newly developed micro-photoluminescence measurement at low temperature has revealed one-dimensional diffusion of excitons in GaAs quantum wires with the lateral width of 7 - 30 nm fabricated by the selective growth technique using metal-organic chemical vapor deposition. The observed diffusion length increased with decreasing the wire width from 30 to 15 nm, and decreased from 15 to 7 nm, where the maximum diffusion length was about 4 μm for the 15-nm quantum wire. The change of the diffusion length vs. the wire width is expected to be due to the competition between the one-dimensional character and the interface fluctuation.
Theory of Semiconductor Microcavities and Lasers
Authors: Koch S.W. , Jahnke F. , Schneider H.C.
Published: February 2023

A fully quantum mechanical theory for the coupled electron-hole-pair and photon dynamics of semiconductor microcavity systems is presented. Based on a nonequilibrium Green’s functions approach, the carrier system is described by a generalized Boltzmann equation which includes contributions for carrier generation, carrier scattering by other carriers and phonons, as well as the spontaneous and stimulated recombination. The photon dynamics is described in terms of coupling to the carriers as well as by the mode confinement through the cavity. The many-body Coulomb effects are included on the level of a screened Hartree-Fock approximation.
Luminescence processes in semiconductor microcavities
Authors: Houdré R. , Weisbuch C. , Stanley R.P. , Oesterle U. , Pellandini P. , Ilegems M.
Published: February 2023

The interaction of light with semiconductors has always triggered a huge effort both because of its importance in determining fundamental processes and parameters and because of the numerous applications which depend on it. One process of particular importance is luminescence which allows such wide-scale applications as lasers, LEDs and displays.
Nonlinear Vacuum Rabi Splitting in Semiconductor Microcavities
Authors: Rhee J.-K. , Lai R. , Norris T. B. , Arakawa Y. , Nishioka M.
Published: February 2023

Recently, several research groups have reported investigations of vacuum-field Rabi splittings (VRS) in the linear response of strongly coupled semiconductor microcavities [1-4]. We have previously reported on the dynamics of time-domain vacuum Rabi oscillations, which are most easily understood in the framework of cavity exciton-polaritons, in which the in-plane momentum k|| is conserved [2], so that at each k|| a single cavity mode interacts with only a single mode of the electromagnetic field (Jaynes-Cummings model). In high Q semiconductor microcavities, the strong coupling between two-dimensional excitons and planar distributed- Bragg-reflector cavity modes results in several-meV splittings observable in the reflectivity or absorption spectrum. In the low excitation regime, the VRS is independent of light intensity incident on the cavity, since the vacuum-Rabi frequency exceeds the externally-driven Rabi frequency (in which case the Jaynes-Cummings model is equivalent to the linear dispersion of the coupled exciton-cavity system). As the incident light intensity is increased, two different effects may be expected to contribute to the nonlinear response. First, as long as the excitonic absorption is equivalent to a two-level system, higher-lying states of the Jaynes-Cummings ladder might be observable. Second, at high intensity phase-space filling and Coulomb screening of the exciton states results in a reduced oscillator strength which leads to a reduced VRS; this effect has no analogue in the case of atom-cavity systems. In this paper, we apply several ultrafast nonlinear techniques to investigate the nonlinear response of semiconductor microcavities.
Radiation Pattern of Spontaneous Emission from Microcavity DBR Surface Emitting Lasers
Authors: Hamano Tetsuko , Koyama Fumio , Iga Kenichi
Published: February 2023

The control of spontaneous emission in microcavity has been extensively studied in order to search for ultimate performances of vertical-cavity surface emitting lasers (VCSELs) such as ultra-low threshold operation [1,2], high-speed modulation and so on. It is interesting to investigate the radiation characteristic from microcavity DBR, and some works on planar microcavity (PLMC) were studied theoretically and experimentally [1-3]. From their results, it is reported that the radiation patterns from PLMC were not isotropic due to the modification of the standing waves in the microcavity, and that the patterns are dependent on the detuning of cavity resonant wavelength and emission peak wavelength However, we cannot apply such radiation characteristic from PLMC for a microcavity VCSEL that has a finite cavity in all the direction. To study the radiation pattern from a microcavity VCSEL, therefore, we may assume a post-type or pillar-type three-dimensional microcavity (3DMC) whose mesa size is also comparable to several wavelengths long (~a few microns).
Characterization and optical device applications of porous silicon
Authors: Münder H.
Published: February 2023

The electrochemical process used to form porous Si layers (PSL) is known for more than 30 years. The spongelike microscopic structure of PSL depends on the substrate properties, the doping concentration and the type of doping, as well as on the etching parameters. The pore size can range from μm to nm depending on the substrate parameters. For a given doping concentration the porosity can be varied by changing the current density. E.g., for p = 1019cm-3 the porosity can be varied from about 30 to 80% by changing the current density from 10 to 250 mA/cm2. The remaining Si structure is still single crystalline. Therefore, PSL have been used as patterned substrates for the heteroepitaxial growth of III-V layers on Si wafers. In addition, PSL can be used for the formation of silicon-on-insulator (SOI) structures.
Polymers in Optical Micro cavities
Authors: Feldmann J. , Lemmer U. , Hennig R. , Ochse A. , Hopmeier M. , Göbel E.O. , Guss W. , Pommerehne J. , Mahrt R. , Bässler H.
Published: February 2023

The control of the emission properties of light-emitting devices is currently a subject of intense research in the field of inorganic as well as organic semiconductor physics [1]. The possibility to suppress or to enhance the spontaneous emission rate by using optical microcavities [2] is of particular interest, since this can lead to an enhanced light emission [3,4].
1.32 μm room temperature photoluminescence from InGaAs quantum dots on GaAs
Authors: Mirin Richard , Ibbetson James , Nishi Kenichi , Gossard Arthur , Bowers John
Published: February 2023

InP is the preferred substrate for long wavelength (1.3-1.55 μm) optoelectronic devices because of the relative ease of growing epitaxial layers of InGaAsP which have the necessary bandgaps and lattice constants. GaAs is not used as a substrate for the growth of these devices because of the difficulty of growing an epitaxial layer of InGaAs with a high enough In content and proper thickness due to the large lattice mismatch. In this paper, we will show that growing InGaAs quantum dots on (100) GaAs substrates allows us to obtain room temperature photoluminescence (PL) at wavelengths as long as 1.32 μm with a full width at half maximum (FWHM) of only 32 meV.
Dipole Emission in Two-Dimensional Photonic Band Structures
Authors: Suzuki Toshio , Yu Paul K. L. , Smith D. R. , Schultz S.
Published: February 2023

For non-conducting passive two-dimensional dielectric periodic structures, the wave equation with a source term J(x,y,t) for an electric dipole can be written as, where
J(x,y,t)=J(x,y)J(t)=I0Ωdδx−x0y−y0θ(t)e−iΩt. The dyadic Green's function
G¯x,y,t;x′,y′,t′ satisfies,
G¯x,y,t;x′,y′,t′ can be constructed with the eigen solutions of the homogeneous wave equation, The eigen solutions of (4) with properly normalized eigenvectors can be readily obtained by the plane wave method.
Waveguide-Coupled Microcavity LEDs
Authors: Pezeshki Bardia , Kash Jeffrey. A. , Kisker David. W.
Published: February 2023

The ability to modify the spontaneous emission of an atom in a micro-cavity has introduced a new degree of control which may have profound significance for opto-electronic devices1. In compound semiconductors, distributed Bragg mirrors on the two sides of an active quantum well lead to narrow-band emission in the cavity mode2. Generally, these cavities are optimized for normal incidence geometry, and the light is monitored perpendicular to the layers. However, at room temperature, and under strong pumping conditions, the light is emitted in a broad range of wavelengths. The presence of the microcavity causes each wavelength to be generated at a different angle and thus the narrow band emission wavelength changes with angle. In this work we show that micro-cavities can be optimized to emit at an angle that corresponds to a waveguide mode, and thus they can directly couple to an adjacent waveguide. Since the emission bandwidth depends directly on the cavity thickness, one can use a taper in the device to controllably generate many wavelengths into the same waveguide. Such a device could be used for multi-wavelength communication through the same optical fiber.
Spin Quantum Beats in Quantum Wells and Wires
Authors: Rühle W. W. , Oestreich M. , Hannak R. , Heberle A. P. , Nötzel R. , Ploog K. , Köhler Klaus
Published: February 2023

Recently, the observation of spin quantum beats in time-resolved photoluminescence after picosecond excitation of GaAs quantum wells (QWLs) was reported.[1] A semiclassical description of this novel experiment follows: The circularly polarized laser generates an electron spin polarization in z direction according to the transition rules (Fig. 1). The magnetic field in the perpendicular x-direction forces these spins into a Larmor precession around the x direction, i.e., the electron spin polarization changes periodically with the Larmor frequency between parallel and antiparallel to the z direction. As a consequence, light emitted in z direction periodically oscillates between the two circular polarizations. A typical example is shown in Fig. 2 for a high quality 25nm QWL with an inhomogeneous broadening of the heavy-hole exciton line of 300μeV. [1]
Polarization characteristics of vertical-cavity surface-emitting lasers with tilted waveguide region
Authors: Chu Hye Yong , Yoo Byueng-Su , Park Min Soo , Park Hyo-Hoon
Published: February 2023

Control of the polarization state for vertical-cavity surface-emitting lasers (VCSELs) is one of the critical issues for polarization sensitive optical systems. In conventional VCSEL structures, the nearly degenerated orthogonal polarization states with fundamental mode are observed at and above threshold. However, in the absence of the selectivity of a polarization state, unstable polarization switching occurs and results in an excess intensity noise by mode hopping. A stable polarization operation over wide current range is required for low noise applications. Several attempts have been made to control the polarization of VCSELs.[1-3] A birefringent metal/dielectric polarizer on the top distributed Bragger reflector (DBR)[1] and an anisotropic gain medium of fractional-layer superlattice structure[2] were introduced. Choquette et al. [3] examined anisotropic transverse cavity like rhombus- or dumbbell-shape and obtained strong polarization selectivity for a specific direction. In this work, we propose a simple method to control the polarization direction by tilted-etching of laser pillar. This structure can select a single dominant polarization state with an electric field perpendicular to the tilted direction. We also demonstrate switching of the two polarized beams in form of 2x4 array in which a switching unit consists of a pair of laser devices tilted with different directions.