Tsing-Hua Her

THREE-DIMENSIONAL OPTICAL STORAGE INSIDE TRANSPARENT MATERIALS

We present a novel method for three-dimensional optical data storage that has submicrometer size resolution, provides a large contrast in index of refraction, and is applicable to a wide range of transparent materials. Bits are recorded by use of a 0.65-N.A. objective to focus 100-fs laser pulses inside the material. The laser pulse produces a submicrometer-diameter structurally altered region with high contrast in index of refraction. We record binary information by writing such bits in multiple planes and read it out with a microscope objective with a short depth of field. We demonstrate data storage and retrieval with 2-microm in-plane bit spacing and 15-microm interplane spacing (17 Gbits/cm(3)). Scanning electron microscopy and atomic force microscopy show structural changes confined to an area 200 nm in diameter.

Microstructuring of silicon with femtosecond laser pulses

We report that silicon surfaces develop an array of sharp conical spikes when irradiated with 500 laser pulses of 100-fs duration, 10-kJ/m2 fluence in 500-Torr SF6 or Cl2. The spikes are up to 40-μm tall, and taper to about 1-μm diam at the tip. Irradiation of silicon surfaces in N2, Ne, or vacuum creates structured surfaces, but does not create sharp conical spikes.

40 Gbit/s pseudo-linear transmission over one million kilometers

Single-channel 40 Gbit/s pseudo-linear (non-soliton) transmission over 1000000 km of nonzero dispersion fiber is achieved using all-optical 2R regeneration and in-line synchronous modulation after every 400 km (4/spl times/100 km). Measured Q factors are better than 19 dB at several distances from 400 km to 1000000 km.

Surface femtochemistry of 02 and CO on Pt(111)

Abstract Desorption of OZ and formation of CO2 were induced with subpicosecond laser pulses on a Pt(111) surface dosed with coadsorbed OZ and CO. We report the fluence dependent yields obtained over a range of laser wavelengths from 267 to 800 nm, and pulse durations from 80 fs to 3.6 ps. The nonlinear dependence of the yield on fluence is different at different wavelengths. Two-pulse correlation measurements show two different time-scales relevant to the desorption. The results show that nonthermalized electrons play a role in the surface chemistry, and that an equilibrated pre-heating of the surface modes leads to enhanced desorption.

Group-velocity dispersion measurements in a photonic bandgap fiber

Spectral interferometry with a supercontinuum is used for the first experimental measurement, to our knowledge, of phase dispersion of the fundamental mode in multiple bandgaps of a photonic bandgap fiber. The dispersion data show a strong influence of the Bragg scattering from the crystal structure surrounding the core. A simple two-dimensional model that includes the effects of a wavelength-dependent angle of propagation, where the angle is determined by the Bragg-scattering condition, and the effects of thin-film-like resonant scattering planes in the fiber is found to explain the observations qualitatively.

Surface femtochemistry of CO/O2/Pt(111): The importance of nonthermalized substrate electrons

We studied the surface femtochemistry of CO/O2/Pt(111) induced with 0.3 ps laser pulses over a wide range of wavelength and fluence. Below 10 μJ/mm2, the yields depend linearly on fluence. Above 10 μJ/mm2, the yields scale nonlinearly in the fluence. From the dependence of the yields on wavelength, we determine that the nonlinear surface femtochemistry is influenced by nonthermal substrate electrons.

REACTION PATHWAYS IN SURFACE FEMTOCHEMISTRY : ROUTES TO DESORPTION AND REACTION IN CO/O2/PT(111)

Abstract We present new data that address the chemical pathway to desorption of O 2 and formation of CO 2 in CO/O 2 /Pt(111) induced by subpicosecond laser pulses. The data show conclusively that the O 2 desorbs molecularly. We also find that if the CO oxidizes by an atomic pathway then the capture of oxygen atoms by the CO is highly efficient; if the CO oxidizes by a molecular pathway then the oxygen atoms in the CO 3 ∗ transition state are inequivalent.

Dispersion monitoring and automatic compensation based on a differential nonlinear detection scheme

Using nonlinear optical detection to provide time-domain pulse distortion information and a novel differential measurement scheme to isolate the effect of chromatic dispersion and to determine its sign, real-time dispersion measurement and automatic compensation is demonstrated.

Experimental demonstration of a fiber-based optical 2R regenerator in front of an 80Gbit/s receiver

We demonstrate, for the first time to our knowledge, an 80 Gbit/s optical 2R regenerator based on self phase modulation in fiber. The potential improvement in receiver sensitivity and tolerance to degraded optical signal-to-noise ratio is investigated.

Novel conical microstructures created in silicon with femtosecond laser pulses

Summary form only given. Silicon wafers are mounted inside a vacuum chamber backfilled with gas and then irradiated with 800-nm pulses from a regeneratively amplified Ti:sapphire laser. Following laser treatment, the samples are removed from the chamber and analyzed with a scanning electron microscope (SEM).