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At least 739 records · Page 41Linked to original sources
PubMed2002

Spatiospectral transmission of a plane-mirror Fabry-Perot interferometer with nonuniform finite-size diffraction beam illuminations.

The transmission of a plane-mirror Fabry-Perot (PFP) interferometer is theoretically modeled and investigated by treating the spatial and spectral features in a unified manner. A spatiospectral transfer function is formulated and utilized to describe the beam propagation and the multiple-beam interference occurring in an ideal one-dimensional strip PFP interferometer with no diffraction loss. The spatial-frequency filtration of a finite-size beam input not only determines the transmitted spatial beam profile but also plays a crucial role in affecting the overall spectral transmittance. The inherent deviations of the spectral transmittance from what we know as the standard Airy's formula are revealed in diverse aspects, including the less-than-unity peak transmittance, the displacement of a resonance peak frequency, and the asymmetric detuning profile. Our theoretical analysis extends to the misaligned PFP interferometers, such as the cases in which non-normal-incidence beams or wedge-aligned mirrors are used that could severely degrade the effective interferometer finesse.

Journal Article↗
PubMed2006

Modeling, simulation, and open-loop control of a continuous facesheet MEMS deformable mirror.

We introduce a coupled system of nonlinear partial differential equations (PDEs) to model a particular microelectromechanical systems (MEMS) deformable mirror consisting of a continuous facesheet coupled with electrostatic plate-driven actuators. To make the problem computationally tractable, we reduced the system to a single linear PDE for the facesheet coupled with nonlinear algebraic constraints for each of the actuators. We also introduce a nonlinearly constrained quadratic optimization problem for open-loop control of the MEMS mirror. Numerical simulation and control results are presented, and shortcomings of the model are discussed.

Journal Article↗
PubMed2003

Low-loss submicrometer silicon-on-insulator rib waveguides and corner mirrors.

Rib microwaveguides are demonstrated on silicon-on-insulator substrates with Si film thickness of either 380 or 200 nm and a width of 1 microm. Corner mirrors that allow compact 90 degrees turns between two perpendicular waveguides are characterized. Measured propagation losses are approximately 0.4 dB/cm and approximately 0.5 dB/cm for 380-nm and 200-nm Si film, respectively, and mirror losses are approximately 1 dB. This allows the development of applications such as optical interconnects in integrated circuits over propagation distances larger than several centimeters.

Journal Article↗
PubMed2003

Passive mode locking of a diode-end-pumped Nd:GdVO4 laser with a semiconductor saturable absorber mirror.

We report an end-pumped and passive mode-locking all-solid-state laser. The laser consists of a Nd:GdVO4 crystal and a linear resonator with a semiconductor saturable absorber mirror that yield mode locking. We achieved stable continuous-wave mode locking with an 8-ps pulse duration at a 154-MHz repetition rate. The average output power was 600 mW with 4 W of pump power. To our knowledge this is the first report of the use of a Nd:GdVO4 crystal for mode locking with a semiconductor saturable absorber mirror.

Journal Article↗
PubMed2003

Mo:Y multilayer mirror technology utilized to image the near-field output of a Ni-like Sn laser at 11.9 nm.

Although bright x-ray sources exist at shorter wavelengths, the development of sophisticated diagnostics with x-ray laser sources has been restricted to wavelengths longer than 12.5 nm because of the limitations of the widely used Mo:Si multilayer mirrors. With the novel Mo:Y multilayer mirrors that we present, many x-ray laser applications can be extended to the 7-12-nm range. We demonstrate this new capability by imaging the near-field output of the Ni-like Sn laser at 11.9 nm.

Journal Article↗
PubMed2003

14.5% near-normal incidence reflectance of Cr/Sc x-ray multilayer mirrors for the water window.

Cr/Sc multilayer mirrors, synthesized by ion-assisted magnetron sputter deposition, are proved to have a high near-normal reflectivity of R = 14.5% at a grazing angle of 87.5 degrees measured at the wavelength lambda = 3.11 nm, which is an improvement of more than 31% compared with previously published results. Elastic recoil detection analyses show that the mirrors contained as much as 15 at. % of N and traces of C and O. Soft x-ray reflectivity simulations reveal interface widths of sigma = 0.34 nm and an exceptionally small layer thickness drift of approximately 1.6 x 10(-5) nm/multilayer period throughout the stack. Simulations show that a reflectivity of R = 25.6% is attainable if impurities and layer thickness drift can be eliminated. The abrupt interfaces are achieved with ion assistance with a low ion energy of 24 eV and high ion-to-metal flux ratios of 7.1 and 23.1 during Cr and Sc sputter deposition, respectively. In addition, a near-normal incidence reflectivity of 5.5% for the C VI emission line (lambda = 3.374 nm) from a laser plasma source was verified.

Journal Article↗
PubMed2004

Piezo-driven deformable mirror for femtosecond pulse shaping.

We have developed a deformable, gold-coated mirror based on piezoelectric actuators with 15-micros response time. With 20 independent channels we were able to compress 72-fs pulses from a Ti:sapphire oscillator down to 45 fs in a 4f zero-dispersion compressor arrangement. Spectral interference was used to measure the mirror performance, while the spectral phase interferometry for direct electric field reconstruction (SPIDER) technique was used for the laser pulse characterization.

Journal Article↗
PubMed2005

Compression of attosecond harmonic pulses by extreme-ultraviolet chirped mirrors.

In the race toward attosecond pulses, for which high-order harmonics generated in rare gases are the best candidates, both the harmonic spectral range and the spectral phase have to be controlled. We demonstrate that multilayer extreme-ultraviolet chirped mirrors can be numerically optimized and designed to compensate for the intrinsic harmonic chirp that was recently discovered and that is responsible for temporal broadening of pulses. A simulation shows that an optimized mirror is capable of compressing the duration from approximately 260 to 90 as. This new technique is an interesting solution because of its ability to cover a wider spectral range than other technical devices that have already been proposed to overcome the chirp of high harmonics.

Journal Article↗
PubMed2005

Pyramid sensor for segmented mirror alignment.

We report what is to our knowledge the first laboratory experiment that shows the use of a pyramid wavefront sensor to cophase and align segmented mirrors having three degrees of freedom per segment, i.e., piston, tip, and tilt. In the laboratory the iterative alignment procedure reached a wavefront residual error of about 10 nm. The residual error was equally distributed between piston, tip, and tilt. These results demonstrate that the pyramid can successfully simultaneously sense the piston, tip, and tilt of a segmented mirror. This last feature makes this technique very attractive in phasing and aligning astronomical segmented telescopes such as extremely large telescopes currently under extensive studies.

Journal Article↗
PubMed2006

Solid-state laser spectral narrowing using a volumetric photothermal refractive Bragg grating cavity mirror.

Dramatic spectral narrowing of two normally broadband lasers, Ti:sapphire and Cr:LiSAF, was achieved by simply replacing the output mirror with a reflective, volumetric Bragg grating recorded in photothermal refractive glass. The output power of each laser was unchanged from that obtained using dielectric coated output mirrors with the same output coupling as the Bragg grating while spectral brightness increased by 3 orders of magnitude.

Journal Article↗
PubMed2006

Optically driven microelectromechanical-system deformable mirror under high-frequency AC bias.

A new, optically addressed deformable mirror device is demonstrated. The device consists of a pixellated metalized polymeric membrane mirror supported above an optically addressed photoconductive substrate. A conductive transparent ZnO layer is deposited on the back side of the substrate. A very high-frequency AC bias is applied between the membrane and the back electrode of the device. The membrane is deformed when the back of the device is illuminated because of impedance and bias redistribution between two cascaded impedances. We fabricated, demonstrated, and modeled the operation of this device.

Journal Article↗
PubMed2006

Generating a high-extinction-ratio pulse from a phase-modulated optical signal with a dispersion-imbalanced nonlinear loop mirror.

We demonstrate a method for generating ultrashort pulses from a phase-modulated optical signal by using a dispersion-imbalanced nonlinear loop mirror instead of the traditional linear dispersion medium. The extinction ratio of the pulses is greatly improved at the same time. By controlling the bandwidth of the phase-modulated signal and the dispersion map of the dispersion-imbalanced nonlinear loop mirror, we can control the pulse width from several picoseconds to hundreds of femtoseconds.

Journal Article↗
PubMed2006

Brewster-angled chirped mirrors for broadband pulse compression without dispersion oscillations.

We use Brewster-angled chirped mirrors for dispersion compensation of a noncollinear optical parametric amplifier. This novel mirror design virtually eliminates spurious surface reflections and resultant dispersion ripple. The absence of compression artifacts is demonstrated by the generation of clean 5.6 fs pulses, with what is believed to be an unprecedented low ripple-induced satellite content for a nonadaptive scheme. In addition, the 270 THz spectral coverage allows generation of widely tunable visible pulses of 8 to 15 fs duration.

Journal Article↗
PubMed2006

Dichroic mirror embedded in a submicrometer waveguide for enhanced resonant nonlinear optical devices.

We report the design, fabrication and characterization of novel dichroic mirrors embedded in a tightly confining AlGaAs/Al(x)O(y) waveguide. Reflection at the first-harmonic wavelength as high as 93% is achieved, while high transmission is maintained at the second-harmonic wavelength. The measured cavity spectrum is in excellent agreement with finite-difference time-domain simulations. Such a mirror is essential for achieving resonant enhancement of second-harmonic generation.

Journal Article↗
PubMed2002

A case of peripartum cardiomyopathy with a transient increase of plasma interleukin-6 concentration occurred following mirror syndrome.

Peripartum cardiomyopathy (PPCM) is an unusual heart failure of unknown etiology that occurs during pregnancy or postpartum. Mirror syndrome is a characteristic of maternal edema subsequent to fetal and/or placental edema. We report a case of PPCM with a transient increase of interleukin-6 concentration occurring in the postpartum period of mirror syndrome.

Adult↗
PubMed2006

Dreams that mirror the session.

Dreams in which the analyst appears undisguised almost always depict violations of the setting. Often experienced as special, epiphanic moments, they give a glimpse of an intense, emotional reaction to traumatogenic or otherwise significant events that have occurred during the session or in the most recent previous ones. Probably, the essential aspect of these dreams can be found in the 'form of their content'. This may be paralleled by the narrative technique of mise en abyme or mirror-text. The dream appears as a story within the main story and the scene of the analysis is reflected anti-illusionistically. The fictional structure of the setting is emphasized. Its theatrical self-consciousness quality is revealed at its best. The author postulates that the transformative therapeutic value of these dreams derives from denouncing the referential illusion of 'concrete reality' and of 'what really happened'. For the analysand, they are an effective (i.e. emotionally intense) opportunity to discover the spatial articulations and the staggering refractions of the inside/outside, the textual/extra-textual, the psychic reality/material reality. In the continual comings and goings from one term to another, the work of symbolization is reactivated and the subject is constructed. Dreams that mirror the session, from this point of view, provide a model for conceptualizing the analytic work, and their significance goes beyond the specific phenomena referred to. A clinical case is given, in which some of one patient's dreams are considered as they occurred over a short period. In one of them, the dream-within-a-dream phenomenon is present.

Adult↗
PubMed2006

Synchronization between background activity and visually evoked potential is not mirrored by focal hyperoxygenation: implications for the interpretation of vascular brain imaging.

We performed an electroencephalography and optical topography study simultaneously exploring electrophysiological and vascular response magnitude as a function of stimulus frequency. To elicit a response in the visual cortex, subjects were exposed to flicker frequencies varying from 1 to 25 Hz (1 Hz steps, eyes closed). Extending the standard view to compare magnitudes of the evoked neuronal to the evoked vascular response, we additionally investigated modulations of alpha-power, a marker of "background" EEG activity. The results show two discrepancies between the electrophysiological and vascular response: (1) VEP and alpha-power exhibit a discontinuous peak when stimulating at the individual alpha-frequency (IAF) (approximately 10-11 Hz), indicating resonance between background oscillations and evoked response; this is not mirrored by the vascular response. (2) The vascular response, in contrast, steadily increases up to a maximum at 7-8 Hz and slightly decreases with higher frequencies. This continuous frequency dependence is partly reflected by the decrease in alpha-power up to frequencies of 8-9 Hz and a slight increase in alpha-power beyond the IAF resonance. Although indicating an inverse relationship between alpha-power and vascular response, the frequency dependence of the evoked response does not show such a correlation. Thus, electrophysiological resonance between an individual's alpha-frequency and isofrequent stimulation is not mirrored by the vascular response. Also, spontaneous background EEG activity is an important modulator of the vascular response magnitude. We discuss these deviations from a simple one-to-one translation between evoked potential and vascular response amplitude in the light of questions concerning synchronization, attenuation, and induction of background oscillations such as the alpha-rhythm.

Adolescent↗
PubMed1980

A case of hand mirror cell variant of acute lymphoblastic leukemia.

A 30 year old female patient diagnosed as acute lymphoblastic leukemia (ALL) with hand mirror like configuration of lymphoblastic-lymphocytic cells is reported. Although the leukemia was resistant to conventional chemotherapeutic regimens, the patient always looked well and survived for more than 20 months. Surface marker analysis showed that the cell was non-T, non-B, and not reactive to antiserum against common ALL antigen. A cytogenetic study of all the analyzable metaphases of the direct bone marrow preparation had a normal female karyotype. The clinical and hematological course is described. The immunological significance and the influence of hand mirror cell on chemosensitivity and prognosis are discussed.

Adult↗