Mohammad R. Taghizadeh

Room temperature, visible wavelength optical bistability in ZnSe interference filters

Abstract The observation of milliwatt-power optical bistability at room-temperature in interference filters based on ZnSe spacers is reported. Switching times of a few milliseconds have been achieved using 514 nm wavelength radiation at an irradiance of ∼250 W cm -2 . The device has been operated in a steady-state manner and switched between the two stable states by an external beam.

Comparing glass and plastic refractive microlenses fabricated with different technologies

We review the most important fabrication techniques for glass and plastic refractive microlenses and we quantitatively characterize in a systematic way the corresponding state-of-the-art microlenses, which we obtained from selected research groups. For all our measurements we rely on three optical instruments: a non-contact optical profiler, a transmission Mach–Zehnder interferometer and a Twyman–Green interferometer. To conclude, we survey and discuss the different fabrication techniques by comparing the geometrical and optical characteristics of the microlenses, the range of materials in which the lenses can be produced, their potential for low-cost fabrication through mass-replication techniques and their suitability for monolithic integration with other micro-optical components.

Multiphoton multifocal microscopy exploiting a diffractive optical element

Multiphoton multifocal microscopy (MMM) usually has been achieved through a combination of galvo scanners with microlens arrays, with rotating disks of microlens arrays, and cascaded beam splitters with asynchronous rastering of scanning mirrors. Here we describe the achievement of a neat and compact MMM by use of a high-diffraction-efficiency diffractive-optic element that generates a multiple-spot grid of uniform intensity to achieve higher fidelity in imaging of live cells at adequate speeds.

Iterative algorithm for the design of diffractive phase elements for laser beam shaping

An improved iterative algorithm for designing diffractive phase elements for laser beam shaping in free space is presented. The algorithm begins with the Gerchberg-Saxton approach to obtain a stable solution. This is followed by several new iterations, in which modified constraining functions are imposed in the Fourier domain while the phase distribution of each iteration remains unchanged. For super-Gaussian beam shaping suitable for inertial confinement fusion applications the mean-square errors of the amplitude and the intensity profile of the entire beam fitted to the corresponding parameters of the 12th-power super-Gaussian beam are approximately 0.035 and 9.75x10(-3), respectively. Approximately 97.4% of the incident energy is converged into the desired region.

Nonlinear Optical Circuit Elements As Logic Gates For Optical Computers: The First Digital Optical Circuits

The first digital all-optical circuits based on intrinsic bistable devices have now been realized. Experimental results with two systems, InSb etalons and nonlinear interference filters containing ZnSe, are presented and discussed. These results indicate that a digital optical processor incorporating devices of this type would appear to be feasible.

Thermally induced optical bistability in thin film devices

A simple theoretical model describing thermally induced optical bistability is discussed. Results of experimental studies of optical bistability in ZnSe interference filters near the band edge are in good agreement with the predictions of this model.

Propagation characteristics of coherent array beams from carbon dioxide waveguide lasers

The characteristics of coherent array beams generated by waveguide carbon dioxide laser structures have been investigated, with particular emphasis on their propagation and transformation properties. Methods of array beam generation are presented, and measurements of array beam quality are given through the use of the M/sup 2/ parameter. Efficient transformation of an array beam from the antisymmetric to symmetric pattern is achieved through the use of a binary phase plate, and spatial filtering is shown to improve the beam quality at the expense of only a moderate loss of total beam power. Coherence effects in the near-field propagation of array beams are also explored.

Optical bistability in bulk ZnSe due to increasing absorption and self‐focusing

We report the first observation of cavityless optical bistability in ZnSe. A shift in the band edge and self‐focusing occurs due to the temperature rise of the material as the laser irradiance is increased. These two mechanisms are believed to provide the feedback necessary for bistable operation.

Realization of an InSb bistable device as an optical and gate and its use to measure carrier recombination times

We report the novel operation of a natural reflectivity InSb bistable resonator at 77 K, pumped with a cw CO laser at 1819 cm−1, as a single pulse detector with definite threshold energy and as an optical AND gate. The two switching pulses for the AND gate logic operation are 30‐ps single, switched‐out pulses from a mode‐locked neodymium: yttrium aluminum garnet (Nd:YAG) laser. Introduction of a variable time delay between the logic pulses provides a unique technique for measurement of the photogenerated carrier lifetime and yields a recombination time ∼90 ns for a cw CO holding intensity ∼80 W/cm2.

Diffractive optical elements for high gain lasers with arbitrary output beam profiles.

We introduce a previously unreported laser cavity configuration, using a diffractive optical element (DOE) in place of the output coupler. Such a configuration allows the DOE to work both in reflection, as a mode shaping element, and in transmission as a beam shaper. Employing dual wavelength DOE optimization techniques and phase delays greater than 2pi, allows the two functions to be designed independently. Thus, an arbitrary output beam profile can be combined with a mode shape which maximizes energy extraction from the gain medium. Devices are designed and their performance modeled for a 1m cavity with 5mm diameter mirrors and a wavelength of 632.8nm. An element with 32 quantization levels and a maximum phase delay of 8pi in transmission produces high quality results.