New, fundamental resonant properties of laser resonators are theoretically predicted and experimentally demonstrated. These resonances occur either in the time dependence of the beam width and that of beam radius of curvature of the wavefront or in the time dependent pointing and position stability of the output light beam of a laser resonator. The resonant frequency can be tuned continuously from zero to the round-trip frequency in the first case; and from zero to the half of the round-trip frequency in the second case, by for example, moving one of the mirrors of the resonator. In both cases besides a resonant frequency its complementary frequency to the round-trip frequency is also resonant, and their shifted frequencies by multiples of the round-trip frequency are also resonant. In our experimental demonstration we measured the radiofrequency noise spectrum of the output laser beam, that was partially blocked by a knife-edge. We observed increased noise at the theoretically predicted frequencies. Similar resonances are predicted either in the time dependent pulse-width and phase modulation or time jitter and the central frequency of the ultrashort light pulses of the node-locked lasers because of the analogy between the space description of the light beams and the time-description of the light pulses.
Novel plasmonic sensor chips are prepared by generating sub-micrometer periodic patterns in the interfacial layers of bimetal-polymer films via master-grating based interference method. Poly-carbonate films spin-coated onto vacuum evaporated silver-gold bimetallic layers are irradiated by the two interfering UV beams of a Nd:YAG laser. It is proven by pulsed force mode AFM that periodic adhesion pattern corresponds to the surface relief gratings, consisting of sub-micrometer droplet arrays and continuous polymer stripes, induced by p- and s-polarized beams, respectively. The characteristic periods are the same, but more complex and larger amplitude adhesion modulation is detectable on the droplet arrays. The polar and azimuthal angle dependence of the resonance characteristic of plasmons is studied by combining the prism- and grating-coupling methods in a modified Kretschmann arrangement, illuminating the structured metal-polymer interface by a frequency doubled Nd:YAG laser through a semi-cylinder. It is proven that the grating-coupling results in double-peaked plasmon resonance curves on both of the droplet arrays and line gratings, when the grooves are rotated to an appropriate azimuthal angle, and the modulation amplitude of the structure is sufficiently large. Streptavidin seeding is performed to demonstrate that small amount of protein can be detected monitoring the shift of the secondary resonance minima. The available high concentration sensitivity is explained by the promotion of protein adherence in the structure's valleys due to the enhanced adhesion. The line-shaped polymer gratings resulting in narrow resonance peaks are utilized to demonstrate the effect of therapeutic molecules on Amyloid-&Bgr; peptide, a pathogenic factor in Alzheimer disease.
Chirped dielectric rugate mirrors have been constructed for broadband dispersion control in femtosecond laser oscillators by the use of Fourier transform. Dispersive properties of the mirrors are tailored and explained on the basis of the time shifting theorem of Fourier analysis. Depending on their construction parameters, these chirped gradient-index structures may exhibit high reflectivity and nearly constant negative, i.e. anomalous group delay dispersion over frequency ranges well beyond the fluorescence bandwidths of broadband laser- active materials available to date. As a consequence, practical implementation of these novel dispersive devices would permit the full utilization of the bandwidth offered by these broadband gain media, and allow the construction of small size, compact femtosecond solid state laser oscillators generating optical pulses shorter than could have been achieved so far, directly from the laser oscillator.
A discrete structure consisting of peaks separated by hv photon energy was found experimentally in the photoelectron energy spectrum, when illuminating a gold target surface by relatively long light pulses (approximately nanoseconds) and using moderate (approximately 120 MW/cm2) intensity of Nd:glass lasers (λ = 1.06 μm). This structure can be considered as the above-threshold photoeffect (ATP) of metal surfaces. Its occurrence at surprisingly low laser intensities [which are four orders of magnitude less than the typical intensity range of the analogous above-threshold ionization (ATI) of atoms] was observed when the space charge was considerably eliminated.
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