bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of the amplitude-modulated inverse filter for pattern-recognition applications
Authors: Zheng S. H. , Kraim M. A. , Gao M. L.
Published: February 2023

An amplitude-modulated phase-only filter1, referred to here as an amplitude-modulated inverse filter (AMIF). The AMIF function is given by (1) where D and A can be constants or functions of both u and v, |R(u,v)| is the amplitude of Fourier spectrum of the reference function r(x,y), and (u,v) is the phase factor of R(u,v). The constraint D |R(u,v)| min+A guarantees that the gain of an AMIF based correlator is less than or equal to unity for all frequency values. When A < |R(u,v)|, AMIF is found to have a good correlation discrimination (CD) just as that of an IF and when A > |R(u,v) |, it is found to have a good optical efficiency (OE) as that of a phase-only filter (POF). By choosing values for A between the limits A < |R(u,v)| and A > |R(u,v)|, all the transition states between a POF and IF can be obtained. POF delivers nearly 100% OE and IF delivers the best CD. The AMIF allows for a trade-off between OE and CD and is shown to be very flexible to meet the pattern recognition applications. Our results show that AMIF has a better CD performance than that of a POF in the absence and presence of noise.
Consequences of the normalization of correlation filters
Authors: Dickey Fred M. , Romero Louis A.
Published: February 2023

The technique of using correlation filters for optical pattern recognition has received considerable study.1 Several variations on the matched filter have been suggested. They include phase-only filters (POFs), binary phase-only filters (BPOFs), complex ternary matched filters (CTMFs) and synthetic discriminate functions (SDFs). Generally, in the development of optical correlation filters, little attention has been given to the normalization of the filter output. Goodman suggested that the matched filter be normalized by means of the Cauchy–Schwarz inequality.2 The Cauchy–Schwarz inequality can be applied to arbitrary correlation filters. This normalization achieves intensity invariance. It can be seen that the matched filter achieves the maximum normalized value of unity. For all other correlation filters, a value less than unity is obtained. In general, it can be shown that for filters other than the matched filter, there are objects that give normalized correlation outputs greater than the object for which the filter was made. This simple normalization has consequences for the design, bandwidth selection, and discrimination ability for the above mentioned filters. The results of analysis and simple examples will be presented.
Bloch-vector model for dressed states of resonant Raman interaction
Authors: Shahriar M. S. , Hemmer P. R.
Published: February 2023

It is well known that the resonant Raman interaction optically pumps atoms into a non-absorbing dressed-state.1 When this state is long-lived compared to the optical Rabi frequencies and the decay rate of the intermediate state, many interesting dynamics arise. These dynamics are significant in applications such as Raman clock AC–Stark shifts, microwave phase-sensitive optical absorption,2 and Raman cooling. By using appropriate approximations, we show that these dynamics can be well described with a Bloch-vector model, which involves only ground-state populations and coherence. This ground-state Bloch-vector model resembles the Bloch-vector model of a two-level system, but it has subtly different dynamics. Furthermore, we construct a novel dressed-state Bloch-vector that clearly shows the analogy between conventional optical pumping and coherent Raman trapping. In this model, one dressed-state is a nonabsorbing state, and the other is an absorbing state. We use the dressed-state Bloch vector to show how Raman AC–Stark shift arises and how it depends on experimental parameters. We also show how the microwave phase-sensitive optical absorption can be quantitatively calculated in a simple way.
Backseeded stimulated photorefractive scattering phase conjugation in SBS niobate fibers
Authors: Hesselink Lambertus , Mullen Ruth Ann , Pepper Dave
Published: February 2023

Back-seeded stimulated photorefractive scattering phase conjugation is demonstrated in SBN fibers for the first time. A 7 mm long by 0.8 mm diameter 0.01% Ce:SBN fiber oriented with its c-axis along the length of the fiber is used for the measurement. The seed is provided by placing a retroreflecting screen in the path of the beam that is transmitted by the fiber. Reflectivities of 28% and 49%, accounting for reflection losses, are achieved by using light with wavelengths of 515 nm and 638 nm, respectively. Previously seeded stimulated phase conjugation (SSPC) has been demonstrated in bulk photorefractive BaTiO3,1,2 by using retroreflector arrays. Good fidelity of the back-reflected signal is achieved with reflectivities approaching 60%. The geometry for optimum results requires that an index-matching fluid surround the crystal; pixel-based image processing-appears to be difficult to achieve in bulk crystals. In the new approach a synthetic material is constructed by bundling SBN fibers. This allows parallel, pixel-based image processing to be accomplished3 with low-power (milliwatt) laser beams. By employing a polarization beam splitter in conjunction with a wave plate, the reflected light can be coupled out without loss in amplitude. We report on the angular sensitivity, wavelength dependence, and amplitude threshold needed for SSFC to occur in these fibers.
Stability of solitons in randomly varying birefringent fibers
Authors: Wai P. K. A. , Menyuk C. R.
Published: February 2023

Because of the presence of linear birefringence, single-mode fibers are really bimodal. It has been shown1 that in the case of constant birefringence, walk-off can be avoided by modulation; the two fractional pulses shift each other's central frequency such that any initial difference in group velocity is eliminated. As a result, they are self-trapped in the time domain. In real fibers, the orientation of the birefringence tends to shift randomly, scattering light from one polarization to another in the process. A simple model2 has been used to study the effect of this random variation on solitons. The fast and slow axes are assumed to flip randomly at given intervals. It is found that for sufficiently small fiber polarization-dispersion parameters, splitting and excessive pulse broadening can be avoided. In this paper, the effect of random variation of birefringence is studied in more detail. Besides allowing for different orientations and a range of magnitudes of the birefringence, a finite autocorrelation length is also considered.
Correlation of birefringence and lattice imperfections in L-arginine phosphate single crystals
Authors: Rao S. M. , Batra A. K. , Lal R. B.
Published: February 2023

L-arginine phosphate (LAP) a new organic nonlinear optical material. It has both a higher conversion efficiency and a higher damage threshold than does D*KDP. We report the first study of the correlation of lattice defects and the changes in birefringency brought about by them in LAP. In all the crystals grown by low-temperature solution crystal growth technique, a central region near the seed crystal with high dislocation density (~106/cm2) is observed. This region is correlated with noticeable birefringency changes by means of a birefringency interferometer.1 Its influence on the damage threshold for high-power lasers will be discussed. Also, a possible origin of the region will be discussed, from the crystal growth point of view, along with remedies to reduce it or avoid its formation in order to ensure better optical quality crystals.
Two-photon and tree-carrier absorption in glass optical fibers
Authors: Carlson K. , Osterber U.
Published: February 2023

Despite several calculations1,2 discussing the possibility that self-phase modulation (SPM) and cross-phase modulation (CPM) are the main factors for saturation with length of second-harmonic (SH) light in optical fibers, we believe that we have experimentally proven3 that SPM and CPM have a very limited influence on the variation of saturation with length for the SH light in an optical fiber. Instead, we propose that absorption plays a major role, both for saturation as a function of length and for overall saturation as a funciton of time. Assuming the absorption has two contributions, one from a resonant two-photon transition of fundamental and harmonic photons in the germanium oxide molecules of the glass and the second from photo-induced absorption based upon free-carriers, we can explain most of the experimentally found anomalies3 of saturated SH light with length and time. We will also discuss various possibilities for photo-inducing free carriers in doped fused silica.
Blue-Stark shift of the excitons in optimized asymmetric coupled quantum wells
Authors: Guo C. L. , Ding Y. J. , Li S. , Khurgin J. B. , Law K. K. , Stellatot J. , Law C. T. , Kaplan A. E.
Published: February 2023

Asymmetric coupled quantum wells (ACQWs) were used to study red-Stark shift of the excitons.1 On the other hand, the blue-Stark shift for the optimized ACQW was predicted.2 Here, we report our photo-current measurements (or the optimized ACQW structure at 78K. The optimized ACQW sample was grown using molecular beam epitaxy and consisted of 25 × (a 18-A GaAs well, a 15-A Al0.4Ga0.6As tunnel barrier, a 32-A GaAs well, and a 100-A Al0.4Ga0.6As separating layer). The water has been processed into mesa diodes with ACQWs in the intrinsic region of p-i-n diode. Argon-pumped cw dye laser was used for photo-current study. Our calculations showed that a field of ~50 kV/cm was required to bring the lowest hole energy levels of two wells into resonance and to increase the oscillator strength of the lowest excitonic transition. Since a built-in field of ~21 kV/cm was measured from I-V curve, the externally applied bias required for resonance was calculated to be about 2.1 V. In our experiment, at the reverse bias ~2.25 V, the sharp increase in the photo-current peak was observed for laser intensity ~9.2 mW/cm2, indicating the resonance between the lowest hole levels in the ACQWs and confirmingourpredictions.2 We also observed the unusually large blue-Stark shift of the heavy-hole excitons up to 6.1 meV (27 A). The external bias ranges at which the resonance occurs at much narrower than what predicted, and may be explained by the transverse excitonic effect.
Stereo images of fluorescence micrographs through maximum-likelihood estimation
Authors: Liu Yi-Hwa , Holmes Timothy J.
Published: February 2023

The expectation-maximization (EM) algorithm based on maximum-likelihood estimation (MLE) has been used for restoring simulated quantum-limited noncoherent imagery in our previous work.1 Its performance in these computer simulations has motivated us to further test the algorithm on three-dimensional (3-D) real data. In recent experiments, we used an accelerative version of the EM algorithm for this testing.2 3-D optically sectioned images of a fluorescently labeled biological specimen were used in these experiments. These 3-D real data were collected as a stack of 32 128 × 128 images. To reduce the computer execution time and memory space, instead of reconstructing the full 3-D image, we reconstructed a pair of stereo images by applying the slice theorem of computerized tomography (CT). Fig. 1 shows the 17th slice out of the stack of the 32 collected images. This image contains both in focus and out of focus portions. A stereo pair reconstructed by MLE after 100 iterations is shown in Fig. 2.
Laser induced locking of solid-melt patterns on semiconductors
Authors: Dworschak K. , Sipe J. E. , van Driel H. M.
Published: February 2023

A silicon surface continuously illuminated by a laser forms patterns consisting of distinct regions of solid and melt. These patterns have previously been categorized as having ordered or disordered morphologies.1 Through the use of two-dimensional Fourier transforms, we have more completely characterized the solidmelt patterns. The Fourier transforms of both morphological types exhibit structures with a characteristic spatial frequency. The transform structures of the disordered patterns exhibit wide spectral widths and no orientational order, distinguishing them from the ordered patterns. The characteristic spatial length associated with the disordered structures is determined by heat flow within the semiconductor. When approaches the wavelength of the incident light, then electrodynamic effects begin to lock in, generating patterns with distinct orientations and spatial periods related to the polarization and wavelength of the laser.
Period-doubling route to chaos in a standing-wave laser
Authors: Tarroja Manuela Fe H. , Casperson Lee W. , Sicam Arni , Chenkosol Pilak
Published: February 2023

The direct comparison between numerical and experimental results on the chaotic behavior of laser systems has been limited because the detection mechanisms usually allow only one or, at most, two aspects of their dynamical behavior to be observed simultaneously. Using a digital oscilloscope, we are able to observe simultaneously the temporal and spectral behavior as well as the corresponding phase plot of the output from a xenon laser, which is detected by a fast InAs detector. As the excitation current of the laser is increased, the laser exhibits a period-doubling route to chaos. Casperson's standing-wave model assumes an inhomogeneous broadening due to Doppler effect, includes the velocity-changing collisions, and uses the slowly-varying amplitude approximation. The model is described in Ref. 1. For numerical parameters consistent with the xenon properties and the experimental set-up, data sets of real and imaginary field amplitudes are generated for different values of excitation. From these, the intensity as a function of time, the power spectrum, and phase plot are calculated. The results show good qualitative agreement with the experimental results.
Model of electroretinogram photocurrent response
Authors: Breton Michael E. , Montzka Dan
Published: February 2023

The electroretinogram (ERG) is a component electrical response originating in radially oriented elements of the retina. The two major early components have opposite polarity at the cornea and are generated by the photoreceptors and inner retinal elements. These components combine algebraically to produce the a- and b-wave features of the ERG. Reconstruction of the photoreceptor component of the response as a function of intensity is an important research and clinical goal. Photoreceptor response for excised rods has been modeled as the output of a cascade of linear low-pass filters, modified to account for response compression, in response to a brief flash of light.1 This low-pass impulse-response model has also been fitted to the leading edge of the ERG a-wave.2
Theoretical model for second-harmonic generation in germanosilicate glass
Authors: Lawandy N. M.
Published: February 2023

The problem of efficient second-harmonic generation in germanosilicate optical fibers and bulk MOCVD glass is explained in terms of the existence of optically driven carrier delocalization of midgap states. At intensities above ~10 GW/cm2, most of the localized states within the gap become delocalized, resulting in directional charge transport, a large frozen-in dc field, and a discontinuous jump in the effective (2).1 The experimentally observed threshold is associated with a delocalization transition that occurs when the photon-renormalized disorder energy between sites is lowered to a value near the tunneling-energy bandwidth, resulting in a type of insulatormetal transition. At lower energies, weak delocalization of states occurs between sites with smaller energy separations, leading to shorter-range charge transport, weaker dc fields and a lower effective (2). The model is consistent with many of the observed experimental results, such as seeding-mode dependence, the measured time evolution, and recent magnetic field experiments.
Infrared erasure of optically induced χ(2) grating in high-GeO2-content optical fibers
Authors: Hibino Y. , Mizrahi V. , Stegeman G. I. , Sudo S.
Published: February 2023

The χ(2) grating that is induced by intense infrared pulses in GeO2-doped silica fibers has previously been shown to be erasable by green light.1,2 Here we report the erasure of the χ(2) grating by prolonged exposure to infrared light only. We used two kinds of small- core GeO2-doped silica fibers: fibers A and B have GeO2 contents of 19 mol% and 4 mol%, respectively. The fibers were seeded with 1064 nm light and its second harmonic (SH) 532 nm light by using a mode-locked and Q-switched Nd:YAG laser. The SH conversion efficiencies of the seeded fibers were similar (of order 10−3), despite the quite different GeO2 concentrations. Although the SH power of fiber A decreased with time while reading with the 1064 nm light only, such a decay was not observed in fiber B, even at the same 1064 nm intensity. Moreover, the decay rate of the SH power in fiber A increased with increasing 1064 nm reading power. It was found that the decay rate is proportional to the 4th power of the 1064 nm power. This suggests that the decay of the χ(2) grating is due to the two-photon absorption of the generated SH light, which is caused by Ge-related defects.
Measurement of heating and energy storage in diode-pumped Nd:YLF
Authors: Kahan O.
Published: February 2023

I report the measured ratio of heat to stored energy for a Nd:YLF diode-pumped rod. The lasing medium is heated by nonradiative processes of the lasing ions and by direct absorption by the host. Typically, the ions are pumped to an energy level above the metastable state and, upon radiating, may terminate at a level above ground. The energy difference between the pumped energy level and the fluorescence photon energy, the quantum defect, typically contributes heat. Population quenching of the ions in the metastable state also contributes heat. The host lattice and the pump cavity walls must absorb all pump light that is not absorbed by the lasing pump light that is not absorbed by the lasing ions. This can be significant in flashlamp pumping, in diode pumping away from the absorption lines, and in lightly doped materials. The ratio of heat to stored energy was about 0.7 in a 1% atomic doped Nd:YLF rod that was diode pumped for 200 s with sigma- polarized light centered at 806 nm. This is less than the reported value of similarly pumped Nd:YAG.1
Arrays of focused beams generated by the integration of Fresnel microlenses with vertical cavity surface-emitting laser arrays
Authors: Rastani K. , Orenstein M. , Kapon E. , Von Lehmen A. C.
Published: February 2023

The advent of vertical cavity surface emitting laser arrays (VC-SELAs) creates new possibilities of integration and miniaturization in a host of optical information processing and interconnection applications.1,2 Beams of individual lasers in a VC-SELA exit through the substrate while diverging due to diffraction causing beam overlap after short distances. Here, we present results of integrating an easy to fabricate binary phase Fresnel microlens array (BP-FMA) on the substrate of a VC-SELA to focus individual beams making them suitable for above applications. A VC-SELA with 10 m aperture laser on 100 m pitch was first fabricated detail of which is given elsewhere.2 By the selective ion beam milling of the substrate, the BP- FMA pattern was fabricated in the exit interface. The generated step height was 0.19 m (to induce 180 phase shift between neighboring zones of Fresnel microlenses). Each microlens in the array has an aperture of 80 m situated 100 m apart. In one case, we used such microlenses to reduce the beam divergence of 10 m aperture lasers (situated 200 m away) from 11 (diffraction without the lens) to 4 (with the lens). In this paper, we will present the quality of beams generated in addition to the diffraction and the throughput efficiencies of the fabricated microlenses. The effect of back reflection on the performance of laser resonators will also be examined.
A computer-aided design tool for planar free space optics
Authors: Downs M. M. , Jahns J.
Published: February 2023

The use of lithographic techniques to fabricate optical components and systems allows one to apply computer-aided design (CAD) tools to their evaluation and layout. Efforts to create such a CAD system have been aimed primarily at computer generated holograms (CGHs).1 We have arrived at a point in the design of planar free-space optics where the complexity and topology of the systems require a dedicated design tool. To this end, we are designing a CAD tool that, in its final stage, will allow the user to lay out the system, generate the electron-beam mask file, and theoretically analyze the optical properties of the system. In this paper, we present a part of the CAD tool that performs the layout and generates the file for an electron-beam (e-beam) lithography system. Because portability of the software is important, we have chosen to use the X-windowing environment.
Optoelectronic shuffle-exchange network for multiprocessing architectures
Authors: Haney Michael W.
Published: February 2023

A shuffle-exchange network based on free-space optical interconnects is proposed for multiprocessor architectures. The processing elements (PEs) are arrayed on a planar rectilinear grid. For packet switching applications, an optical source/detector pair is located at each PE. A folded perfect shuffle (FPS) optical system,1 located above the plane, uses reflective or folded optics to shuffle the array of sources onto the array of detectors. The exchange/bypass function is performed electronically on each pair of PEs. If M source/detector pairs are located at each PE site, then a single FPS optical network can be used for pipelining M stages, effectively forming M interleaved arrays of the N PEs. For each pair of PEs, M electronic exchange/bypass switches route the signals from the output detector of one stage to an input source of the next. The interconnect latency of the network is therefore limited to M times the optical delay in the FPS system. The source/detector arrays are interleaved such that the two-dimensional space- bandwidth product (SBP) of the optical system is most effectively utilized. For example, if N = 1024 and M = log2(N), then the SBP requirement is NM, or about 100 100.
Ferroelectric liquid-crystal waveguiding structures for nonlinear optics applications
Authors: Liu Jian Y. , Robinson Michael G. , Johnson Kristina M. , Doroski David
Published: February 2023

The optical properties of surfaced-stabilized ferroelectric liquid-crystal cells are well documented and have been used to form high-contrast-ratio optical modulators. These structures also exhibit second-order nonlinearities because their polar alignment.1 Waveguiding in the material would be useful both for integration of compact switching elements and for increased interaction length and power density in nonlinear optical applications. We present results from multimode waveguiding structures in smectic C* ferroelectric liquid-crystal surface-stabilized cells. Our presentation includes loss measurements and analysis of the polarization integrity of the eigenmodes of these structures. Preliminary results indicate that losses are below −5 dB/cm measured at = 632.8 nm, which is an improvement upon waveguides made from nematic liquid crystals at this wavelength. Analysis of the polarization of propagating modes has been carried out by using prism-coupling techniques and indicates that the eigenmodes are not pure TE or TM owing to distortions in the layered surface stabilized structure. Further analysis is being carried out by fabricating strip waveguides determined by patterned-electrode structures. These experiments should indicate the feasibility of making such structures into arrays of switching elements.
Demonstration of a free-space 2×2 switching mode using symmetric self-electro-optic-effect device modulators and detectors
Authors: Novotny R. A. , Pawelski R. L. , Veach R. S. , Lentine A. L.
Published: February 2023

A 2 × 2 photonic switching node was demonstrated that switched two 140 Mbps extended quality television signals with error-free performance, using discrete optical components, and extensible arrays of symmetric self-electro-optic-effect device (S-SEED) differential modulators and detectors.1 The switch consisted of two electronically controlled differential GaAs quantum well modulator arrays, one differential GaAs quantum well detector array, and a space invariant interconnection. Laser diodes were used for the optical interconnections. Each differential modulator (detector) consisted of two serially connected MQW diodes (i.e., a symmetric SEED) with the modulating voltage applied to (modulated current detected from) a center tap between the diodes. Two S-SEED cells were used within each 2 × 4 array spaced on a 30 × 40-μm pitch with two 10-μm round windows for each MQW diode. The system was tolerant to laser noise and remained aligned and stable. We show switch performance (speed, cross-talk, BER, energy & power dissipation) and describe possible extensions of this system for backplane (board-to-board) interconnection.
0.5-GHz cw mode-locked Nd:glass laser
Authors: Da Ling Jung , Yan Li , Lee Chi H. , Soos J. I.
Published: February 2023

By harmonically modelocking a Nd:YAG laser 31 ps pulses at 0.5 GHz repetition rate have been obtained.1 By using YLF, shorter pulses, 9.1 ps, at 0.5 GHz repetition rate have been achieved. Nd:Glass has a much wider bandwidth and potentially can achieve a shorter pulsewidth. Our group had achieved a pulsewidth less than 10 ps at a repetition rate of 100 MHz. With further compression, the pulses have been shortened to 30 fs.2 In this work, we have investigated the modelocking of a Nd:phosphate glass laser using high frequency gallium-phosphate (GaP) acousto-optic modulators (AOMs). We have characterized four different acousto-optic modulators. The single pass insertion losses of the four tested modulators ranges from 5% to 13%. The modulation depths of these AOMs with 0.3 W rf power are about 25%. The modulation depth and dynamic loss increase with increasing driving rf power and decrease with increasing frequency. We have achieved modelocking of a short cavity (26 cm long) cw Nd:phosphate laser at 500 MHz repetition rate with the average output power of 20 mW, generating 10 ps pulses at 1.054 µm.
Ultrafast carrier dynamics in a-Si1-xGex:H alloys
Authors: Liu Y. M. , Nighan W. L. , Young D. A. , Fauchet P. M.
Published: February 2023

The ultrafast carrier dynamics in a-Si1-x-Gex:H alloys (energy gap 1.0 to 1.8 eV) were examined using femtosecond time-resolved spectroscopy. Optical pulses from an amplified CPM laser (photon energy = 2 eV and pulse duration d fsec) were used to create a large density (1018 to 1021 cm3) of excited carriers. The time dependence of changes in the reflectivity and transmission were measured with a probe pulse obtained from a white light continuum. By varying the energy of the probe pulse photons to be above or below the energy gap in these materials, the ultrafast electronic and thermal effects1 can be isolated. The effective lifetime of carriers near the mobility edge was found to depend strongly upon the carrier density, becoming as short as 1 ps for the highest densities. The ultrafast rise in lattice temperature indicates that electrons and holes are recombining nonradiatively. The carrier lifetime scales with density in a manner that suggests that the mechanism is Auger recombination2 of geminate electron-hole pairs.
Mathematical reconstruction of color-matching functions
Authors: Romero Javier , del Barco Luis Jiménez , Hita Enrique
Published: February 2023

We have calculated the FFT's of the colormatching functions for the CIE1931 standard observer referred to the XYZ primaries and also a set of real primaries. The results obtained agree with those of Barlow1 on applying the Fourier transform to the Smith and Pokorny's fundamental spectral sensitivities and Benzschawel et al.2 in analyzing color-vision mechanisms based on various different models. From the analysis of the Fourier transform moduli of the color-matching functions, we were able to apply the sampling theorem to get mathematical formulas which led to the reconstruction of them at limiting frequencies of 0.02 or 0.05 cycle/nm. This reconstruction proves to be highly reliable at a sampling interval of 10 nm and perfectably acceptable at 25 nm or even wider intervals.
Effect of ocular chromatic aberration on the luminance modulation transfer function for white light in the reduced eye
Authors: Thibos Larry N. , Zhang Xiaoxiao , Bradley Arthur
Published: February 2023

The reduced schematic eye (the "water eye") accurately describes the magnitude of both transverse and longitudinal chromatic aberration of the human eye.1 The modulation transfer function (MTF) of this model, including the effects of diffraction, is easily calculated for monochromatic light and the results integrated across wavelength to produce a white-light MTF. We investigated how sensitive this MTF is to changes of wavelength-in-focus (i.e., the mean refractive error) and to changes in pupil diameter for a typical (2800 K tungsten) white source. The results indicate that both parameters have significant impact and clear maxima exist. For this source, 570 nm is the optimal wavelength-in-focus for any pupil diameter and a 3-mm pupil is optimal for any wavelength-in-focus. These results are understandable as follows. Although the model is emmetropic for 590 nm, the weight of the luminous efficiency curve shifts the optimal wavelength-in-focus towards shorter wavelengths. The optimal 3-mm pupil balances the tradeoff between the effects of diffraction for small pupils and chromatic blur for large pupils.
Photon statistics for two-state atoms in an optical cavity
Authors: Kimble J. J. , Brecha R. J. , Thompson R. J. , Lee W. D.
Published: February 2023

While for the most part quantum statistical processes in quantum optics are investigated in a weak-coupling regime, it has recently become possible to realize experimentally systems for which the internal coupling coefficient g is comparable to the external dissipative rates. Within this context the subject of our investigation is the quantum dynamical processes for a collection of N two-state atoms strongly coupled to a single mode of a high finesse optical cavity. Our particular system consists of a collection of N~20 Cesium atoms (6S 1/2, f = 4– > 6P 3/2, f = 5 transition at 852 nm) interacting with the TEMoo mode of a spherical mirror cavity of finesse 4 × 104. Of principal importance are the single atom cooperativity parameter C1 = g 2/κγ and the saturation photon number no = g2/8γ 2, where (κ,γ) are the cavity and atomic decay rates. For our system, c1~1 and n0~0.5. In measurements of the joint probability of photoelectric detection we observe photon antibunching and sub-Poissonian photon statistics.1,2 An interpretation of our results in terms of quantum state reduction and interference in a dissipative dynamical setting is presented.2 We emphasize the decisive role played by the quantum fluctuations of a single atom (c1~1), which can result in a field of large variance even in the presence of N>1 atoms.
Filtered correlations in the Jaynes-Cummings resonance fluorescence
Authors: Castro-Beltran Hector Manuel , Sanchez-Mondragón J. J.
Published: February 2023

Atomic inversion revivals are the first evidence of the quantum character of the radiation, predicted by the Jaynes–Cummings model, that are experimentally measurable in cavity quantum electrodynamics.1 We propose another test by studying the two time photon correlations between spectrally resolved components of resonance fluorescence spectrum of the coherent Jaynes–Cummings model. The spectrum raises from spontaneous emission between adjacent energy many folds, whose splitting is given by the Rabi frequency for every Fock state. This originates sideband discreteness that can be observed when the filter bandwidth is smaller than the sideband width (atom-cavity coupling). There is photon correlation only if these photons are from consecutive emissions in the dresssed lader, producing a frequency offset. Also, a photon from a sideband is more likely to be emitted before a photon from the other sideband when detuning is finite, in a fashion analogous to that studied by Aspect et al.2 for free space rf. Moreover, the decay is due solely to the filter bandwidth, reflecting lack of cavity losses. These correlations could be observed in presence of mixed fields, therefore are less dependant on the coherence of the experimental cavity fields than the revivals are.
Compression of optical dark solitons
Authors: Zhao W. , Bourkoff E.
Published: February 2023

Optical dark solitons are shown to undergo amplification and compression under the influence of a constant gain in the nonlinear Schrödinger equation. When the gain is small, the pulse follows a simple adiabatic, perturbative expression. For a fundamental dark soliton input, the pulse remains a single hyperbolic tangent shape and its duration decreases exponentially as a result of the gain. When the gain is large, secondary dark solitons1 are generated and the pulse duration fails to follow the exponential rule during the initial stage of propagation. The duration does, however, decrease exponentially at sufficiently long traveling distances. This property of dark solitons can be utilized to amplify and to compress an initially broad dark pulse into a dark soliton of short duration. Stimulated Raman scattering can be used as a gain mechanism.2 The optical power and time duration requirement in generating dark solitons can thus be relaxed as a consequence of this property.
Hybrid implementation of nonlinear joint-transform correlator
Authors: Javidi Bahram , Tang Qing
Published: February 2023

Nonlinear joint transform correlator (JTC) uses nonlinearity at the Fourier plane to nonlinearly transform the Fourier transform interference intensity.1,2 The nonlinear transformation is implemented by two methods. In one method, an optically addressed spatial light modulator (SLM) that operates in nonlinear mode is used at the Fourier plane to nonlinearly transform the joint power spectrum. In the second method, a hybrid optical processor is used to produce the nonlinear transformation. A charge-coupled device array is used to produce the joint power spectrum and electronic circuit device is used to nonlinearly transform the joint power spectrum. The transformed joint power spectrum is written onto a SLM and the nonlinear correlation signals are produced. In this paper, we provide an experimental investigation of the hybrid optical processor to implement the nonlinear JTC. Experiments are used to determine the correlation peak intensity and peak to sidelobe ratio, and correlation width for various degrees of the nonlinearity used at the Fourier plane. The results are compared with the linear JTC. The nonlinear transformations are performed using a computer interfaced with the CCD array. The experiments are performed in the presence of the input scene noise. The nonlinear JTC experiments indicate that reasonably good correlation performance can he obtained using the hybrid nonlinear JTC.
Multiple image detection by nonlinear joint-transform correlator
Authors: Javidi Bahram , Wang Jun
Published: February 2023

It has been shown that the nonlinear joint transform correlator (JTC) produces good correlation performance compared with the linear correlator.1,2 The nonlinear JTC uses nonlinearity at the Fourier plane to non- Iinearly transform the joint power spectrum. In this paper, we provide an investigation of the nonlinear optical processor when multiple objects are present at the input plane. Experiments are used to determine the correlation peak intensity and peak to sidelobe ratio for various types of multiple targets and images present at the input plane. The experiments are performed in the presence of the input scene noise for multiple identical targets and multiple objects. Various types of thresholding the joint power spectrum and its effect on the performance of the system is investigated. The effects of the space- bandwidth product (SBWP) of the input plane such as the input spatial light modulator SBWP on the position requirements of the input signal and the reference signals is investigated. The system performance for different positions of the input targets is examined. The correlation performance of the nonlinear JTC for multiple target detection is compared with the linear JTC. The experiments indicate that compared with the linear JTC, the nonlinear JTC produces reasonably good correlation performance when multiple objects are present at the input plane.
Temporal response of atmospheric turbulence compensation
Authors: Welsh Byron M.
Published: February 2023

With the advent of adaptive optical imaging systems it has become possible to compensate for the deleterious effects of the atmosphere. Many researchers have quantified the performance of adaptive optical systems with respect to wavefront sensor noise, finite wavefront sampling, finite degrees of freedom in the wavefront reconstruction device, and anisoplanatism. Here we study the performance degradation due to the finite temporal response of the adaptive optical system. As expected, the degradation is a strong function of the time delay between wavefront sensing and wavefront correction. In addition we find that the degradation is a strong function of the aperture size as well as whether overall wavefront tilt is removed. We also find that the degree of compensation is a factor in determining the level of performance degradation. Many of the earlier studies of the effect of time delay are restricted to cases in which neither overall piston or tilt are removed.1,2 These prior results are pessimistic in terms of quantifying the degradation experienced for a given time delay. Our results show that for an aperture of diameter 10ro the time delay can be as large as 0.7ro/v where ro is the Fried coherence diameter and v is the velocity of the turbulence.
Extended beam propagation by Gaussian modes
Authors: Stone James , Hu P. H.
Published: February 2023

We frequently need to know the statistical properties of light propagated through a turbulent atmosphere either for receiving images or for precorrecting for turbulence in a projected beam. The most common approach to determining these properties approximates the unperturbed light by either a plane or spherical wave,1 whichever is more appropriate; often, for extended (but not infinite) sources, neither is appropriate. Lutomirski and Yura2 formulated the so-called extended Huygens principle which introduces an integration over the area of the beam, and Ishimaru3 showed that the fundamental Gaussian mode could serve as a source by using the Rytov approximation. We show that higher-order Gaussian modes of rectangular and circular (azimuthal) symmetry can all be analytically propagated through turbulence. This allows a modal expansion of beams with arbitrary profile.
Isolated zeros in the modulus of Fourier space from the view point of phase retrieval from phase gradient vectors
Authors: Ueda R. , Takajyo H. , Sonoda T. , Kajiwara K.
Published: February 2023

Regarding isolated zeros occurring in the modulus distribution of 2-D Fourier space, using the most simplified model, this paper clarifies: (i) the condition of occurrence including why the zeros occur in pairs; (ii) behavior of phase and phase gradient vectors in their neighborhood; (iii) the reason why phase ambiguity is produced; and (iv) derivation of the phase retrieval condition from the phase gradient vectors without ambiguity.
Determination of field correlations from spectral measurements
Authors: James Daniel F. V. , Wolf Emil
Published: February 2023

Second-order spatial coherence properties of radiation fields are usually determined from measurements of the visibility of fringes in suitable interference experiments.1 In recent years it was demonstrated that spatial coherence properties of sources affect the spectrum of emitted radiation.2 In this paper, we show that such spectral modifications may be utilized to provide a new method for determining spatial coherence properties of fields. We also establish a theorem that applies to sources of a large class, according to which a tradeoff between spatial separation and spectral information is possible in some two-point correlation experiments.
Quantum-optical analysis of Wolf’s spectral shifts
Authors: James Daniel F. V.
Published: February 2023

Not long ago Wolf discovered a modification of the spectrum of radiation due to the spatial coherence of the source.1 His analysis used a model correlation function that demonstrated the effect, without discussing any physical mechanism by which the correlations may arise. This paper presents an analysis of one such physical mechanism, namely, the radiation reaction. Following earlier work by Varada and Agarwal,2 an explicit calculation, performed in the harmonic oscillator approximation, for two radiating atoms in equilibrium with a thermal field reveals a relationship between this effect and the well-known shift of atomic oscillator frequencies due to Lamb.
Closed-loop wavefront reconstruction using multiple laser guide stars
Authors: Ellerbrock Brent L.
Published: February 2023

The performance of an adaptive optics system using a single laser guide star is constrained by laser guide star anisoplanatism and the characteristics of available lasers. Improved performance is theoretically achievable through the use of multiple laser guide stars. Earlier results on wavefront reconstruction in laser guide star systems1 are extended to this more general case. General reconstruction algorithms are evaluated using a linear systems model which accounts for the partially correlated effects of laser guide star anisoplanatism, laser guide star position uncertainty, wavefront sensor noise, deformable mirror fitting error, aperture edge effects and control loop servo bandwidth. Reconstructor wavefront estimation accuracy is optimized subject to linear constraints imposed to insure control loop stability. Reconstructor performance is quantified in terms of the optical system’s modulation transfer function for a system including a 3.5-m primary, a deformable mirror with from 341 to 771 actuators, and a constellation of one or several laser guide stars. The addition of a single, low power, resonant sodium guide star greatly improves the performance of a system using multiple Rayleigh backscatter laser guide stars.
Use of two reflective photodetectors for measuring all four Stokes parameters of light
Authors: Azzam R. M. A.
Published: February 2023

It has been shown previously that all four Stokes parameters of light can be measured using an arrangement of four photodetectors.1 Three of the four detectors are partially reflective and steer the beam in a nonplanar path to the fourth absorbing detector. In this paper schemes that employ only two reflective detectors for measuring all four Stokes parameters are described. The detectors are set for oblique reflection and with noncoincident planes of incidence. Recording the 2 × 1 output signal vector for two angular positions (45° apart) of the two-detector assembly around the incident beam axis provides sufficient information to determine the 4 × 1 Stokes vector. Mechanical rotation can be avoided by using a Faraday rotator in front of a stationary arrangement of two detectors. Another novel scheme uses intermittent optical feedback, with a normal-incidence back-reflecting mirror and a light chopper, to modulate the output signals of the two detectors in a square-wave fashion. The two square waves provide enough data to determine fully the most general state of partial elliptical polarization of incident light. The appropriate instrument matrix and its determinant are derived explicitly, and all possible discrete singularity conditions are shown to be readily avoidable. Implementations in fiber-optic form are also discussed.
Photonic band structure
Authors: Yablonovitch Eli
Published: February 2023

By analogy to electron waves in a crystal, electromagnetic waves in a 3-D periodic dielectric structure should be described by band theory. The idea of photonic band structure1 is rapidly2–5 gaining acceptance. The concepts of reciprocal space, Brillouin zones, dispersion relations, Bloch wave functions, Van Hove singularities, etc., are now being applied to optical waves. If the depth of refraction index modulation is sufficient, a photonic band gap can exist. This is a frequency band in which electromagnetic modes, spontaneous emission, and zero point fluctuations are all absent. Indeed, a photonic band gap cam be essentially ideal provided the dielectric response is real and dissipationless. In addition to the obvious uses in atomic and laser physics, photonic band structure can now begin to play a role in microwave and millimeter wave electronics. Defects can be introduced into the otherwise perfect 3-D structures, creating electromagnetic donor modes and acceptor modes. Effectively, these defects are purely dielectric single-mode high-Q cavities suitable for a range of frequencies from microwaves to the visible. At the outset it was realized1 that a face-centered-cubic (FCC) array in real space would produce the most spherelike Brillouin zone in reciprocal space. This spherelike geometry increased the likelihood that a forbidden gap would overlap all the way around the surface of the Brillouin zone. But is was unclear what should be the shape in real space of the atoms in this FCC array. The history of this field has been a search for that optimal 3-D dielectric geometry, favored by nature and by Maxwell’s equations. During this same period, electronic band theorists began calculating photonic band structure. It rapidly became apparent that the familiar scalar wave band theory, so frequently used for electrons in solids, was in utter disagreement with experiment on photons.7–10 Recently3–5 a full vector-wave band theory became available, which not only agreed with experiment, it successfully highlighted some discrepancies in the experiment.
Quantum theory of soliton propagation: a unified approach based on the linearization approach
Authors: Lai Yinchieh
Published: February 2023

A quantum treatment of soliton squeezing based on the linearization approximation has been carried out numerically.2 are recast more naturally. The new formulation also provides a general approach to calculation of detection noise. With the projection interpretation of homodyne detection, the squeezing ratio can be easily calculated by applying the propagation operator to the characteristic function of homodyne detection instead of the perturbation field operator. All the results in Ref. 1 also can be reproduced naturally. Finally, numerical analysis of fiber ring gyros using squeezed solitons and analysis of modelocked lasers are presented.
(InAs)2(GaAs)5 strained layer and superlattice quantum wells as electroabsorption modulators
Authors: Jupina Michael , Koehler Steffen , Hasenberg Tom , Garmire Elsa , Kost Alan
Published: February 2023

We present, we believe for the first time, an ordered strained superlattice as a quantum well (QW) modulator in the InAs/GaAs material system. This short period strained layer superlattice (SPSLS) can replace ternary strained layered quantum wells1,2 to achieve superior performance. Each QW is composed of the following SPSLS structure: two monolayers of InAs followed by five monolayers of GaAs, repeated five times, followed by another two monolayers of InAs for a well width of 111 Å. This structure confines the heavy holes while the unconfined light holes see a resonant tunneling structure. Only the heavy hole exciton is seen in the absorption spectrum (at 975 nm). Both the field and propagation direction were normal to the growth planes when electroabsorption was measured. A reflection sample (double pass) had a peak ΔR/R of 40% at 5 V. The peak in modulation depth occurred below the exciton peak, contrary to other QCSE modulators,1,2 because the wave functions within the SPSLS-QW lose oscillator strength slowly. Using Δα/α as a figure of merit, at 5 V the SPSLS gave Δα/α = 1.8 compared to 1.2 for strained layered ternary quantum wells.2