Ian C. McMichael

Control and measurement of ultrashort pulse shapes (in amplitude and phase) with femtosecond accuracy.

The performances of a tunable femtosecond dye laser are analyzed using accurate correlation techniques. The source is a passively mode-locked dye laser, of which both the frequency and frequency modulation are controlled by one or two intracavity prisms. Interferometric second-order autocorrelations, with a peak-to-background ratio of 8 to 1, are used simultaneously with the conventional intensity autocorrelation and the pulse spectrum to determine the pulse shape. The main advantages of the interferometric autocorrelations are that they provide phase information otherwise not available, and they are more sensitive to the pulse shape than the intensity autocorrelation. The phase sensitivity is demonstrated in an analysis of the Gaussian pulses with a linear frequency modulation. Analytical expressions for the envelopes of the interferometric autocorrelations of typical pulse shapes are provided for quick pulse shape identification. A numerical method is used to analyze the more complex pulse shapes and chirps that can be produced by the laser. A series of examples demonstrates the control of this laser over various pulse shapes and frequency modulations. Pulse broadening or compression by propagation through glass is calculated for the pulse shapes determined from the fittings. Comparisons of autocorrelations and cross correlations calculated for the dispersed pulses, with the actual measurements, demonstrate the accuracy of the fitting procedure. The method of pulse shape determination demonstrated here requires a train of identical pulses. Indeed, it is shown that, for example, a train of unchirped pulses randomly distributed in frequency can have the same interferometric autocorrelation than a single chirped pulse. In the case of the present source, a comparison of the pulse spectrum, with that of the second harmonic, gives an additional proof that pulse-to-pulse fluctuations are negligible.

Electro-Optic Power Limiter: Broadband, Self-Actuating Optical Limiter for Visible and Infrared Radiation

We present studies of an optical power limiter that uses a combination of the photoconductive and linear electro-optic effects. The electro-optic power limiter (EOPL), first demonstrated using CdTe in the near IR, possesses many desirable qualities including broadband wavelength responsivity, self-actuation, and low threshold power. One unique capability of EOPL, not found in any other nonlinear optical power limiter, is the fact that any light - coherent or incoherent - can be used. Our studies in CdTe, GaAs, and BSO crystals resulted in extending the wavelength range from the visible to MWIR wavelengths.

Subpicosecond Pulse Shape Measurement and Modeling of Passively Mode Locked Dye Lasers Including Saturation and Spatial Hole Burning

We present a theoretical model of the linear and ring, passively mode locked dye lasers. This simple model gives a clear understanding of the role of the amplifier, the absorber, and the dynamics of the degenerate third order nonlinearity resulting from spatial hole burning [1].

Two-photon organic photochemistry for 2-D spatial multiplexing in volume holographic storage

The two-photon photochemistry described here is a potential candidate for 2-d spatial multiplexing in volume holographic storage. The initial diffraction efficiency obtained in these materials is promising. Issues remain with understanding and avoiding the decay of the initial diffraction efficiency, and with reducing the absorption of the exciting wavelength without simultaneously reducing the diffraction efficiency. The ease of manufacture of the two-photon photochemical system compared with the inorganic photorefractives makes them attractive for the holographic storage application.

Application of Laser and Related Materials to Demonstrate Large Nonlinear Optical Effects and Diffraction Efficiency

Long metastable lifetimes in laser and related materials combined with a large index change makes possible large nonlinear optical effects using cw lasers. We describe experiments demonstrating such effects using the solid state laser material Cr:YAlO3, and we show how studies of the spectroscopy and kinetics can be used to understand the results. Since the same optical nonlinearity will affect the propagation of beams, it should be considered in the design of lasers.