The condition for a diffuser to produce the maximum speckle contrast reduction with the minimum number of distinct phase patterns is derived. A binary realization of this optimum diffuser is obtained by mapping the rows or columns of a Hadamard matrix to the phase patterns. The method is experimentally verified in the Grating Light Valve laser projection display.

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The Grating Light Valve TM (GLV TM ) is a diffractive MOEMS spatial light modulator capable of very high-speed modulation of light combined with fine gray-scale attenuation. GLV-based products are field-proven in a variety of applications. In this paper, we describe the GLV device, its structure, theory of operation, and optical performance. The versatility and speed of the GLV device are described. We explain how the GLV device is integrated into an optical write engine to create a complete digital imaging system. In addition to the MOEMS die and drive electronics, the light engine also comprises illumination optics, Fourier filter, and imaging optics. We present current applications of the GLV device for high-resolution displays, and computer-to-plate printing, as well as future plans for digital imaging applications opened up by the unique properties of this diffractive MOEMS technology.

Comment on "Energy Conservation in the Picosecond and Subpicosecond Photoelectric Effect"In a recent Letter, Yablonovitch 1 pointed out that a full accounting of energy balance in the subpicosecond photoelectric effect must include the blueshift induced on the laser pulse by the ionization event itself. He showed that this extra energy acquired by photons not absorbed in the ionization process is mathematically equivalent to the "quiver energy" e 2 E 2 /4mco 2 of the freed electrons in the peak electric field E of the light pulse.In our judgment, this Letter correctly describes the overall energy balance in the subpicosecond photoelectric effect, but ambiguously describes the energy transfer to the light field which produces the blueshift. This ambiguity occurs because the "ionization event" is a complex sequence consisting of the light-neutral-atom interaction during the leading edge of the pulse, generation of a free electron at time to, quivering of the free electron in the remaining part of the pulse, and passage of the trailing edge. When during this complex process does the blueshift occur? Yablonovitch is ambiguous on this point. Although his analysis identifies the blueshift with "the phase modulation during the ionization process at *o" -i.e., the instant of generation of the free electron -he later ascribes the blueshift-incorrectly, in our judgement-to events in the trailing edge of the pulse: quivering electrons which "remain behind in the focal volume. . . cede their discrete quiver energies to a blue shift of the laser beam as a whole." The recently developed capability to observe blueshifts with femtosecond pulses 2 permits these two pictures of the blueshift dynamics to be distinguished experimentally. To support our argument we present a new femtosecond pump-probe measurement which shows unambiguously that the blueshift occurs at the expected instant of ionization to, which because of ionization saturation occurs well in the leading edge of a sufficiently intense pulse, not from a delayed transfer of electron quiver energy to the light field in the trailing edge of the pulse. Figure 1 (a) presents a calculation of the blueshift of a weak 100-fs, 620-nm probe pulse propagating collinearly with, and at varying time delays At within, a 100-fs, 620-nm pump pulse focused at//2 to peak intensity 10 16 W/cm 2 in 1-atm argon gas. At this intensity dN/dt, obtained by modeling ionization probability using Keldysh theory and then deriving ionic density growth from a rate-equation analysis, reaches maximum at At = -60 fs, a measurable time interval before the electron quiver energy peaks and subsides. The Drude model predicts that the probe blueshift tracks dN/dt in time, resulting in maximum blueshift also at At = -60 fs. Figure 1(b) shows the results of a corresponding experiment per-FIG. 1. (a) Calculation of blueshifted spectra of a 100-fs probe pulse at various time delays from the peak of a strong ionizing pulse focused to 10 16 W/cm 2 in 1-atm argon, (b) Time-resolved measurement of probe blueshifts.f...

The Grating Light Valve (GLV) spatial light modulator is a unique and proven CMOS process-compatible optical MEMS device. The modulator employs a dynamically adjustable diffraction grating to manipulate an optical signal. Today, the GLV technology is successfully used in high-resolution display and imaging systems, where its high efficiency, large dynamic range, precise analog attenuation, fast switching speed, high reliability, high yield, and the ability to integrate thousands of channels into a single device are fundamental advantages. These same properties make the GLV device desirable for optical telecommunication applications. The optical properties, functionality, device design, and CMOS processing of the GLV will be presented. Challenges and solutions that arise from adapting the current GLV technology to optical telecommunications wavelengths will be discussed. Measured results will be presented that describe GLV performance parameters, including insertion loss, dynamic range, polarization dependent loss, and spectral attenuation accuracy.