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At least 1,081 records · Page 60Linked to original sources
PubMed2004

Quarter-wave discrete wavelet design of dichroic highly reflecting-transmitting mirrors for ultrafast solid-state lasers.

Thin-film wavelets are further analyzed for the design of dichroic mirrors for ultrafast solid-state lasers that provide both high reflectance on the lasing wavelength range and high transmittance of the pump light. Discrete quarter-wave-thick dielectric thin-film structures of homogeneous refractive indices following a quintic-wavelet envelope are considered. Relations for the reflectance on the lasing wavelength range are given. Adding several index-matching quarter-wave layers to both sides of the discrete wavelet optimizes the transmittance of the pump light. The design is further optimized to get minimum phase distortion on the lasing wavelength range.

Journal Article↗
PubMed2004

Picosecond pulse generation and its simulation in a nonlinear optical mirror mode-locked laser.

A nonlinear mirror composed of a lithium triborate crystal and a dichroic output coupler is used to passively mode lock an Nd:YVO4 laser that is pumped by a diode laser array. A mode-locked output power of 3.2 W, a repetition rate of 178 MHz, a pulse width of 8.4 ps, and a beam quality parameter (M2) of 1.27 are obtained at 1064 nm for a pump power of 10.0 W. The numerical simulation for the steady-state pulse width agrees well with the bandwidth-limited value. A double-pass average gain g(ave) is defined by considering the constancy of the output energy. In the simulation g(ave) is kept as a free parameter, and its value required for the bandwidth-limited pulse is found to be 0.047, whereas its calculated value, based on our definition, is 0.057.

Journal Article↗
PubMed2004

Efficient testing of segmented aspherical mirrors by use of a reference plate and computer-generated holograms. II. Case study, error analysis, and experimental validation.

Segmented mirrors present unique challenges to fabrication and testing that are absent for monolithic optics. Since traditional asphere tests do not address segmented optics adequately, we validate a previously developed method to test large quantities of segments accurately, quickly, and economically. In this test, the aspheric shape of each segment is controlled to high accuracy by use of computer-generated holograms, and the radius of curvature is tightly controlled by use of the reference plate. In an adjoining paper [Appl Opt 43, 5303 (2004)] we developed the theory for this test, and now we present a complete system design and optimization for measuring the 1.4-m segments from a 30-m F/1 primary. A complete tolerance analysis predicts a test accuracy of 4.8-nm rms surface and excellent accuracy for controlling the geometry of the segment. In addition, a laboratory demonstration using 30-cm optics is presented that demonstrated 3.9-nm rms surface accuracy.

Journal Article↗
PubMed2005

Coupled-cavity analysis of the resonant loop mirror: closed-form expressions and simulations for enhanced performance lasing.

A coupled-cavity analysis of the resonant loop mirror with a signal flow graph technique is presented. Use of this technique has resulted in simple closed-form expressions for reflectance, transmittance, critical coupling, bandwidth, finesse, gain threshold, and mode splitting. Application of this device to enhance the single longitudinal mode operation of a fiber laser is also proposed. Detailed simulation results show a dramatic reduction in bandwidth and a threefold enhancement of the free spectral range by use of the vernier effect. The formulas and results obtained would also be useful in laser sensors and filters.

Journal Article↗
PubMed2005

High-birefringence fiber loop mirrors and their applications as sensors.

The reflection and transmission characteristics of a high-birefringence fiber loop mirror (HiBi-FLM), which is composed of a standard fiber coupler and one-section or multisection high-birefringence fibers (HBFs), are analyzed and discussed in detail. Theoretical reflectivity and transmissivity expressions for HiBi-FLMs with one-, two-, and three-section HBFs were obtained. The procedure for calculating reflectivity and transmissivity for HiBi-FLMs with n-section HBFs is given. Experimental results have verified the theoretical model. The basic characteristics of the one-section HiBi-FLM when strain and high temperature are applied to HBFs were analyzed and investigated theoretically and experimentally. The experimental results are in good agreement with the theoretical analysis. Furthermore, a strain--temperature sensor that makes use of those characteristics, which is new for applications of HiBi-FLMs, has been proposed and demonstrated.

Journal Article↗
PubMed2005

Phased array 1-to-N-way resonator with a convex mirror for phase conjugation.

Phased array 1-to-N-way resonators can be relevant in the realization of high output powers from semiconductor laser arrays and have significant advantages over Talbot resonators. However, depending on the number of array elements, the intracavity power density on the output facet can be high, resulting in catastrophic optical mirror damage. We present a variant of the original design that overcomes these power density problems while maintaining the desirable phase-locking and power-combining properties.

Journal Article↗
PubMed2005

Principles and design of multibeam interference devices: a microelectromechanical-systems segment-deformable-mirror-based adaptive spectrum attenuator.

Fourier analysis of multibeam interference shows that the total electric field and relative time delay of the beams form a Fourier-transform pair. Fourier-analysis-based multibeam interference analysis and device design is discussed in detail. The principle of the proposed segment-deformable-mirror-based adaptive spectrum attenuator is illustrated.

Journal Article↗
PubMed2005

Resonant-cavity-enhanced p-i-n photodiode with a broad quantum-efficiency spectrum by use of an anomalous-dispersion mirror.

A resonant-cavity-enhanced photodiode with broad filter transmittance and high quantum efficiency was numerically designed and analyzed, fabricated, and validated experimentally. We show theoretically that the quantum-efficiency spectrum broadens because of anomalous dispersion of the reflection phase of a mirror in the device and describe conditions that allow maximal flatness of the transmitted spectrum to be achieved. To demonstrate the concepts we design, fabricate, and characterize a backilluminated In0.47Ga0.53As-based p-i-n photodiode upon a InP substrate. Experimental measurements of the fabricated devices demonstrate a peak quantum efficiency of 0.80 at 1550 nm and a FWHM of transmittance of 35.96 nm.

Journal Article↗
PubMed2006

Double-deformable-mirror adaptive optics system for phase compensation.

Two kinds of algorithm for an adaptive optics (AO) system that uses two deformable mirrors (DMs), one with large stroke and the other with high spatial frequency, to correct different aberrations are described. The algorithms are based on modal method and direction-gradient method, respectively. Numerical simulations for the algorithms have been made. The simulation results indicate that the two DMs in the AO system can correct different aberrations with different characteristics, and the closed-loop performance of a double-DM AO system will be almost the same as that of an AO system that uses a single DM with an ideal stroke.

Journal Article↗
PubMed2006

Application of integrated sensing and processing decision trees for target detection and localization on digital mirror array imagery.

We demonstrate the applicability of integrated sensing and processing decision trees (ISPDTs) methodology to a set of digital mirror array (DMA) hyperspectral imagery. In particular, we demonstrate that ISPDTs can be used to detect and localize targets by using just a few DMA Hadamard frames, so that an entire hyperspectral data cube need not be collected to successfully perform the given task. This suggests that such an integrated sensing-processing suite may be appropriate for extremely time-sensitive pattern-recognition applications.

Journal Article↗
PubMed2006

Bragg mirror inscription on LiNbO3 waveguides by index microstructuration.

Numerous applications in integrated optics, especially those related to multiwavelength telecommunications, require dichroic reflectors for use as narrowband or broadband wavelength-selective filters. Bragg mirrors are excellent candidates for this purpose, and we describe a method of fabricating Bragg grating reflectors in Ti-indiffused Lithium Niobate single-mode waveguides based on holographic masking in association with proton exchange. The holographic setup is employed to record a photolithographic mask directly on the substrate, enabling the inscription of waveguides with both periodic and aperiodic distributed parameters.

Journal Article↗
PubMed2006

Surface roughness of stainless-steel mirrors for focusing soft x rays.

We have used polished stainless steel as a mirror substrate to provide focusing of soft x rays in grazing-incidence reflection. The critical issue of the quality of the steel surface, polished and coated with gold, is discussed in detail. A comparison is made to a polished, gold-coated, electroless nickel surface, which provides a smoother finish. We used the surface height distributions, measured with an interferometric microscope and complemented by atomic-force microscope measurements, to compute power spectral densities and then to evaluate the surface roughness. The effects of roughness in reducing the specular reflectivity were verified by soft-x-ray measurements.

Journal Article↗
PubMed2006

Double-pass rotary mirror array for fast scanning optical delay line.

We have developed a fast scanning optical delay line based on a rotary mirror array. A double-pass configuration is adopted to optimize the fiber-optical coupling and thus minimize the amplitude modulation in the reflected light. The achieved scanning range is extended to over 3 mm. An additional Michelson interferometer is incorporated into the reference arm to achieve high delay repeatability. Such a device is ideal for real-time optical coherence tomography, optical Doppler tomography, and spectroscopic optical coherence tomography.

Computer-Aided Design↗
PubMed2006

Three-flat test solutions based on simple mirror symmetry.

In interferometric surface and wavefront metrology, three-flat tests are the archetypes of measurement procedures to separate errors in the interferometer reference wavefront from errors due to the test part surface, so-called absolute tests. What is believed to be a new class of solutions of the three-flat problem for circular flats is described in terms of functions that are symmetric or antisymmetric with respect to reflections at a single line passing through the center of the flat surfaces. The new solutions are simpler and easier to calculate than the known solutions based on twofold mirror symmetry or rotation symmetry. Strategies for effective azimuthal averaging and a method for determining the averaging error are also discussed.

Journal Article↗
PubMed2006

Propagation properties of a hard-edged diffracted beam generated by a Gaussian mirror resonator.

Based on the scalar diffraction theory, the propagation and focusing properties of a hard-edged diffracted beam generated by a Gaussian mirror resonator were investigated. Explicit expressions for the field distribution of the truncated beam that propagates through a paraxial optical ABCD system were derived in detail. Numerical examples are given to illustrate our analytical results.

Journal Article↗
PubMed2006

Observation of thermal effects due to an optical incident signal and high fluence on InGaAs/InP multiple-quantum-well saturable absorber nonlinear mirrors: evolution of characteristics and time constants.

We observe the effects of a temperature increase on the characteristics of an InGaAs/InP multiple-quantum-well (MQW) saturable absorber (SA) in a microcavity provided by an optical input signal under normal incidence. The temperature increase on the nonlinear mirror (NLM) due to an optical signal depends on the energy time filling factor (FF) of this input signal (analogous to the signal's duty cycle, which is the ratio between the repetition period and the pulse duration) and hence depends on the repetition rate of the signal for a given pulse time width. This increase in temperature is mostly responsible for a shift in the reflectivity spectrum of the device toward higher wavelengths. In this experimental study, we show the shift of the resonance cavity versus the optical input power at high FF, and we evaluate the thermal time constant of an Fe-doped InGaAs/InP MQW NLM. Finally, we report the consequences of such thermal effects and high fluence on the reflectivity and contrast of two different InGaAs/InP NLMs when the input signal FF rises up to 25%, which gets close to telecommunication transmission conditions.

Journal Article↗