Mirror Distance Research Articles

The ‘mirror test’ for estimating visual acuity in infants

ObjectiveThe authors aimed to investigate the association between the distance at which infants fixate their own reflections and visual acuity card testing, and to determine whether this could form the...

Microcavities: tailoring the optical properties of single quantum emitters

We present a general review of different microresonator structures and how they can be used in future device applications in modern analytical methods by tailoring the optical properties of single quantum emitters. The main emphasis is on the tunable lambda/2-Fabry-Perot-type microresonator which we used to obtain the results presented in this article. By varying the mirror distance the local mode structure of the electromagnetic field is altered and thus the radiative coupling of fluorescent single quantum emitters embedded inside the resonator to that field is changed, too. As a result a modification of the optical properties of these quantum emitters can be observed. We present experimental as well as theoretical results illustrating this effect. Furthermore, the developed resonator can be used to determine the longitudinal position of embedded emitters with an accuracy of lambda/60 by analyzing the excitation patterns of nano-sized fluorescent polymer spheres after excitation with a radially polarized doughnut mode laser beam. Finally, we will apply this resonator to a biological system and demonstrate the modification of Förster resonant energy transfer (FRET) efficiency by inhibiting the excited state energy transfer from the donor to the acceptor chromophore of a single DsRed protein.

Ion beam profiling of aspherical X-ray mirrors

We present a fast and robust ion beam etching technique to profile initially flat surfaces into aspherical ones. The surfacing method is based on the displacement at variable speed of a double-blade system placed between a broad ion beam source and a mirror, thus allowing a spatial modulation of the ion dose along the mirror surface. The fabrication process was validated using various metrology techniques to assess both mirror figure and finish. The method was successfully applied to produce two strongly elliptically shaped mirror prototypes (source–mirror distance 150 m and demagnification 3000). The residual slope errors were found to be 18 μrad over a mirror length of 40 mm while the root mean squared roughness remains below 0.2 nm for spatial periods less than 130 μm.

Compact imaging spectrometer combining Fourier transform spectroscopy with a Fabry-Perot interferometer

An imaging spectrometer based on a Fabry-Perot interferometer is presented. The Fabry-Perot interferometer scans the mirror distance up to contact and the intensity modulated light signal is transformed using a Fourier Transform based algorithm, as the Michelson based Fourier Transform Spectrometers does. The resulting instrument has the advantage of a compact, high numerical aperture, high luminosity hyperspectral imaging device. Theory of operation is described along with one experimental realization and preliminary results.

Feedback phase sensitivity of a semiconductor laser subject to filtered optical feedback: Experiment and theory

We investigate experimentally and theoretically the dynamics of a semiconductor laser subject to filtered optical feedback. Depending on the feedback strength we find dynamical regimes with different dependence on the feedback phase. In particular, the influence of the feedback phase on cw emission and on frequency oscillations is characterized experimentally. We also measure the dependence of the filter mirror distance on the frequency oscillations. In general, good agreement between experiment and theory is found.

Ion emission measurements and mirror erosion studies for extreme ultraviolet lithography

Mirror erosion by high energy ion emission from extreme UV light sources is one of the main factors contributing to EUVL collector mirror reflectivity degradation. We are measuring ion energy distributions at the mirror distance from the plasma utilizing three different ion diagnostics for the case of tin-doped microscopic droplet laser plasmas. Typical ion energy distributions measured by an electrostatic spectrometer are described. From the ion energy distributions, an estimate of mirror erosion is obtained. The effectiveness of electrostatic field mitigation is evaluated for the EUVL source requirement.

Resonant nano-cluster devices

The resonance-enhanced absorption (REA) by metal clusters on a surface is an effective technique on which to base bio-optical devices. A four-layer device consisting of a metal mirror, a polymer or glass-type distance layer, a biomolecule interaction layer and a sub-monolayer of biorecognitively bound metal nano-clusters is reported. Experiments indicate a strong influence of the resonator homogeneity on the absorption maximum. Layer stability plays an important role in the overall performance of the device. Techniques and optimised lab protocols to set up biochips that use the REA process in the detection are presented. The sensors show one to three narrow reflection minima in the visible and or infra-red (IR) part of the spectrum and therefore they do not suffer from the spectral limitations associated with spherical gold colloids. Metal clusters (synthesised by thermal step reduction) as well as metal- dielectric shell clusters (synthesised by various shell deposition processes) are used to precisely shift the readout of the device to any frequency in the visible and near IR range. Disposable single-step protein chips, DNA assays as well as complex biochip arrays are established that use various DNARNA, antigen-antibody and protein-protein interaction systems.

Resonant nanocluster technology—from optical coding and high quality security features tobiochips

Metal clusters deposited on a substrate and positioned at a nanometric distance from awave-reflecting layer act as nanoresonators able to receive, store and transmit energywithin the visible and infrared range of the spectrum. Among the unique effects of thesemetal nanocluster assemblies are high local field enhancement and nanoscale resonantbehaviour driving optical absorption in the visible and infrared range of the spectrum.In these types of devices and sensors the precise nanometric assembly coupling the localfield surrounding a cluster is critical for allowing resonance with other elements interactingwith this field. In particular, the cluster–mirror distance or the cluster–fluorophore distancegives rise to a variety of enhancement phenomena (e.g. resonant-enhanced fluorescence,REF). Depending on the desired application this ‘resonance’ distance is tuned from 5 up to500 nm.High-throughput transducers using metal cluster resonance technology are based on surfaceenhancement of light absorption by metal clusters (surface-enhanced absorption, SEA).These devices can be used for detection of biorecognition binding as well as structuralchanges in nucleic acids, proteins or any polymer. The optical property made use of in theanalytical application of metal cluster films is so-called anomalous absorption. Anabsorbing film of clusters is positioned 10–400 nm from an electromagnetic wave-reflectinglayer. At a well-defined mirror–cluster distance the reflected electromagnetic field has thesame phase at the position of the absorbing cluster as the incident field. This feedbackmechanism strongly enhances the effective cluster absorption coefficient. These systems arecharacterized by a narrow reflection minimum whose spectral position shifts sensitivelywith interlayer thickness, because a given cluster–mirror distance and wavelength definesthe optimum phase.

Dynamic process during axial magnetic compression of field-reversed configuration for equilibrium shape control

Adiabatic magnetic compression experiments on a field-reversed configuration (FRC) plasma are reported. The compression is performed on a long FRC held in a straight mirror field. The separatrix length of the FRC is limited by the distance between the magnetic mirrors. The mirror distance is compressed in time to 35% of the original one by the compression coil installed inside the chamber, and the separatrix length is shortened to 38%. The separatrix radius of the compressed FRC increases by 56% and the aspect ratio (separatrix length/separatrix diameter) changes from 12.6 to 4.1. Magnetic probes with the compensation circuit are utilized to investigate the dynamic transition phase during the compression. The transition process is found from these measurements to be divided into three stages, where a new equilibrium state is achieved in the final stage.

Evolution of the beam quality factor for various active medium positions within a Gaussian cavity

A 2-m-long plane-parallel cavity with a Gaussian reflectivity mirror has been applied to a XeCl discharge chamber with a 35-cm-long active medium and the temporal evolution of the main parameters of the intracavity laser radiation after reflection on the Gaussian mirror, has been analysed for various active medium positions within the cavity. It is shown that in cavities of equal length and effective Fresnel number, the properties of the intracavity radiation are dependent on the Gaussian mirror distance from the active medium, since the onset of laser action. Indeed, it has been found that the beam quality factor M 2 reaches smaller values by setting the Gaussian mirror closer to the active medium. It is also shown that a theory formerly developed for the evolution of the parameters of Schell–Gauss model beams propagating in Gaussian-mirror cavities provides a satisfactory description of experimental results.

Axial length and separatrix radius behavior of field-reversed configuration plasma in dynamic compression of mirror distance

The axial magnetic compression experiment of the field-reversed configuration (FRC) plasma is reported. The FRC produced in the theta-pinch system is translated into the confinement region. The separatrix length of the translated FRC is decided by the mirror distance. The compression is done in a manner as shortening the distance in time. The compression coil is installed inside the chamber to raise the strength of the confinement field at the neighborhood of the mirror. The mirror distance is compressed to be 70% of the original one. The increment of the separatrix radius is observed to be 14%. This is nearly consistent with the adiabatic calculation. The decay rate of the radius has a constant value. From the line integrated density signal measured by the interferometer, no n=2 rotational instability is observed even in the case of the compression.

O(α)Radiative Correction to the Casimir Energy for Penetrable Mirrors

The leading radiative correction to the Casimir energy for two parallel penetrable mirrors (realized by $\ensuremath{\delta}$-function potentials) is calculated within QED perturbation theory. It is found to be of order $\ensuremath{\alpha}$ like the known radiative correction for ideally reflecting mirrors from which it differs, for a mirror distance much larger than the electron Compton wavelength, only by a monotonic, powerlike function of the frequency at which the mirrors become transparent. This shows that the $O({\ensuremath{\alpha}}^{2})$ radiative correction calculated recently by Kong and Ravndal for ideally reflecting mirrors on the basis of effective field theory methods remains subleading even for the physical case of penetrable mirrors.

Talbot Assisted Pattern Formation in a Liquid Crystal Film with Single Feedback Mirror

Abstract We investigated experimentally the spontaneous formation of regular patterns of filaments in a laser beam traversing a thin liquid crystal film placed in front of a single mirror. The transistion from hexagonal to roll-like pattern was experimentally investigated as a function of the laser beam incidence angle and mirror distance. Square patterns were observed by inserting a thin slit behind the mirror. Our observations strongly support a simple model for pattern formation based on Talbot effect.

Improvement of an ECR multicharged ion source

Experimental results are shown for the yield of high charge state ions depending on the field configuration and the type of microwave launcher. The presence of an octupole improves the yield by a factor of 8. A tandem mirror configuration improves the yield by a factor of 7. A multifilar helical antenna on the magnetic axis improves the yield by a factor of 2. Extension of the mirror distance, with the mirror ratio kept unchanged, has little effect on the yield.

Selective properties of gas-laser resonators containing a planar waveguide

A calculation is reported of selective and nonselective losses in a resonator containing a planar waveguide and reflectors located near the waveguide ends. The conditions resulting in degeneracy of the resonator modes are determined. An analysis is made of the influence of geometric and optical parameters of the waveguide, and of the waveguide–mirror distance on the frequency-selective losses in such a waveguide resonator. The results obtained are compared with corresponding results for resonators containing waveguides of different geometry.

Surface damage of single-crystal silicon abraded in ethanol and deionized water

Semiconductor grade, single-crystal silicon wafers of (1 0 0) p-type were abraded by a single-point, slow speed (2.3 cm sec−1) 90° pyramid diamond in ethanol and deionized water. The scratching was carried out in each of the fluids with a load of 0.5 N on the sliding diamond. The scratching produces a groove, the depth of which depends on the number of traverses of the diamond. A measure of the cross-sectional area of the groove was used to determine the abrasion rate in ethanol, which was about 1.3 times that in deionized water. Some of the samples scratched in deionized water were annealed at 1000° C for 1 h and these samples, along with those unannealed and scratched in both fluids, were fractured perpendicular to the scratch in a three-point bend apparatus. The fracture strengths and the mirror distances obtained by scanning electron microscope (SEM) observation were used to deduce tensile residual stresses of 15.6 and 99.0 MN m−2 beneath the grooves formed in deionized water and ethanol, respectively. The SEM investigation also showed that (a) the groove surfaces contained microcracks wedged with wear debris, and (b) dislocations were generated and propagated away from the groove surfaces as a result of annealing. The relatively higher tensile residual stress produced in the presence of ethanol is consistent with the higher wear rate in this fluid.

Coupling efficiency of waveguide laser resonators formed by flat mirrors: Analysis and experiment

We present a new and more efficient method of calculating the losses of a waveguide laser resonator consisting of a hollow circular dielectric waveguide and flat mirrors, taking into account the effects of waveguide modes up to order HE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</inf> . Both symmetric and asymmetric cavities are considered. We show that low cavity losses, only slightly exceeding the HE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> waveguiding losses, are predicted to be possible for much larger mirror distances than had previously been suspected, provided that an optimum total cavity length is chosen. The low losses arise when the HE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> and HE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> modes emerge from the guide with relative amplitudes and phases such that the returning diffraction patterns interfere to produce a narrow beam with low aperture losses. The theoretical predictions were checked experimentally for CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> lasers having various waveguide dimensions. Good qualitative agreement was found, but the optimum total cavity lengths were typically 3-5 percent longer than predicted. Possible explanations of this discrepancy are discussed. We also predicted and experimentally verified that variations of the cavity length over a few centimeters can exert a coarse wavelength selectivity sufficient to determine the band and branch on which a CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser oscillates; conversely, that for a grating tuned laser, the cavity length must be varied by a similar amount as the wavelength is tuned in order to maintain low cavity losses over the entire wavelength range.

Coherent reflection of a Gaussian beam at optical frequencies from a large convex mirror

In some modern laser-system application and performance evaluations, an accurate formula is needed for the spatial distribution of intensity in the reflected or backscattered field that is produced by a coherent Gaussian beam incident upon an optical-grade convex mirror. This paper presents the development of such an analytical formula. The formula is rigorous within the Fresnel approximation, is easy to evaluate, and consists of only a few terms. However, it requires that the mirror size and distance to satisfy the Fresnel condition and the radius of curvature of the mirror be large compared with the wavelength of radiation. With the Gaussian beam transformed to a plane uniform beam and the mirror approximated to a flat circular disk, the formula reduces to the well-known Airy diffraction-pattern formula when subjected to the Fraunhofer condition. Although the formula presented here is strictly applicable only to spherical mirrors with a small aperture-radius-to-radius-of-curvature ratio, when pushed to the full sphere limit, it yields results that have good order-of-magnitude agreement with the machine-calculated results that use the rigorous Mie theory of scattering from a full sphere.

Feedback-stabilized fractional fringe laser interferometer for plasma density measurements

A feedback stabilization technique is described for a fractional fringe interferometer measuring plasma electron densities. Using this technique, a CO2 laser Michelson interferometer with a pyroelectric detector exhibited a sensitivity of 3.4 x 10(-4) fringe on a 1-ms time scale and, due to acoustic pickup, 1.8 x 10(-2) fringe on a 10-ms time scale. The rise time is 45 micros. Stabilization against slow drifts in mirror distances is achieved by an electromechanically translated mirror driven by a servo system having a 0.2-s response time. A mechanical chopper in one of the two beam paths generates the signal which drives the servo system.

PRECISE MEASUREMENT OF SHORT DISTANCES WITH ELECTRO-OPTICAL RANGEFINDERS

Using a plane mirror distances up to 200 m can be measured with a modified differential technique giving a better accuracy compared to distances directly determined with the employed electro optical rangefinder. This method is advocated not only for accurate measurements but also for engineering work, where often vertical distances must be evaluated. Using the Tellurometer MA 100 the height of an 18 floor building has been determined with an accuracy of about ± 0.5 mm.