Richard L. Shoemaker

Demonstration of nonlinear prism coupling

The coupling of light into a waveguide characterized by an intensity dependent propagation constant has been demonstrated experimentally. Limiting action was observed at milliwatt waveguide powers with a liquid crystal medium filling the gap between a prism and a glass waveguide.

Nonlinear distributed waveguide couplers

The efficiency of coupling an external radiation field into an integrated-optics waveguide mode using a distributed coupler such as a prism or a grating decreases with increasing power if one of the waveguide media is characterized by an intensity-dependent refractive index. The differences between the operating characteristics of such a nonlinear coupler and those of the familiar linear coupler are discussed. It is shown numerically that there exists an optimum detuning angle that varies with incident power for optimizing the coupling efficiency. This optimum efficiency, however, is still found to decrease with increasing power. Optimum values of incident-beam spot size and the ratio of spot size to characteristic linear coupling distance are also found to vary with guided-wave power. For coupling into lossy media, the coupling efficiency, which starts out much lower than for lossless media at low powers, becomes comparable with that for the lossless-media case at high powers. Ways of improving the coupling efficiency by using tapered films or chirped gratings are discussed, and calculations are given for specific cases.

Ultrafast laser scanner microscope.

Advances in monolayer deposition of cervical cells have removed one of the last serious obstacles to the design of high-resolution automated diagnostic assessment systems. In this article, we describe the design considerations for a system that is capable of acquiring, within 60 sec, a 0.5 micron digitized image of a 4 cm2 area on a standard glass slide. The most feasible approach is found to be a system using a rotating polygon to sweep the focused spot from a laser across a 2-mm scan line while the slide is uniformly translated perpendicular to the scan direction the use of laser sources (a helium-neon laser at 632 nm and a krypton ion laser at 568 and/or 476 nm) as compared to the incoherent light sources used in conventional microscope systems alleviates many of the optical design problems and provides the proper wavelengths needed for recognition of Papanicolaou stained cells. We also find that focus control of the scanning spot should be achievable using a technique involving a holographic grating. Other relevant considerations such as sample heating problems, multiphoton absorption by the sample, detector signal-to-noise ratios, laser amplitude noise control, and the digitization and buffering of the data stream are also discussed.

An Ultrafast Laser Scanner Microscope for Digital Image Analysis

The design of an ultrafast laser scanner microscope has been completed and an experimental model has been constructed. The instrument is described and the considerations that led to our choice of scanning method and optical and electronic system design are discussed. The scanner incorporates numerous new technologic features, and promises to make high-resolution cell analysis practical at data rates comparable to those obtained now only in flow cytometry.

Periodic Oscillations And Chaos In Optical Bistability: Possible Guided-Wave All-Optical Square-Wave Oscillators

In this paper we report the observation of periodic oscillations and chaos in a hybrid optical bistable system with an optical delay and examine some of the practical aspects of these phenomena. A simple explanation of the square-wave output from such instabilities is given, along with a suggestion for possible all-optical square-wave generators.

Development of an automated scanning monochromator for monitoring thin films.

A scanning monochromator system for the monitoring of thin-film deposition in a box coater is described. The system employs data from both a quartz crystal oscillator and a wideband transmission spectrometer. The spectrometer uses a holographic grating as its dispersive element and a CCD array to collect the data. All data are sent to a microcomputer where the information is displayed, stored, and analyzed. Several applications, including measurement of optical constants of inhomogeneous films and characterization of moisture adsorption, are discussed.

Direct measurements of transition dipole matrix elements using optical nutation

We describe a method of directly determining transition dipole matrix elements which we have used to make the first measurements of this quantity in an asymmetric rotor. A low pressure gas (a few mtorr NH2D) which is subjected to a cw CO2 laser beam is suddenly Stark switched into resonance. An optical nutation signal is detected whose frequency yields ‐E0/h/, where ‐ is the transition dipole matrix element of interest and E0 is the optical field strength which may be determined from power and beam profile measurements. Thus an observation of the nutation frequency along with the power measurements yields ‐. This was done for two transitions of NH2D giving transition dipole matrix elements along two axes in the molecule: 〈ν2=0a‖ (∂μa/∂Q) Q‖ν2=1a〉=0.112±0.009 D and 〈0a‖ (∂μc/∂Q) Q‖1s〉=0.158±0.009 D. The extension of this technique to nonpolar molecules and its advantages over conventional steady state laser methods are discussed.

Anomalous nonlinear guided wave cut‐off phenomena

We show that mode cutoff can occur at finite powers for waves guided by a thin‐film waveguide bounded by one or two media characterized by a defocusing nonlinearity. This phenomenon produced optical limiting action.

Optical coherent transient measurements of velocity-changing collisions in SF 6

Elastic velocity-changing collisions have been observed for the first time to our knowledge in a nonpolar molecule by photon-echo studies of SF(6) using a frequency-switched CO(2) laser that we have developed. The photon-echo decay is nonexponential and reveals the velocity-changing collision cross section to be sigma(vc) = 180 A(2), with an average velocity change per collision of Deltau = 155 cm/sec. Using delayed optical nutation, we also determine the cross section for the population decay rate (1/T(1)) to be sigma(pop)=335 A(2). To within experimental accuracy, we find that phaseinterrupting collisions are not important (T(1) approximately T(2)). A comparison of these cross sections with those for the polar molecule (13)CH(3)F is made.

Machine Vision System for Diagnostic Histopathology

In a machine vision system for the diagnostic assessment of histopathologic sections, human diagnostic knowledge and human ability to recognize components in a complex image need to be emulated. This is attempted by three integrated expert systems, supported by a multiprocessor computer with data-driven, dynamically reconfigurable architecture.