Wilson Garcia

Colored object recognition by digital holography and a hydrogen Raman shifter

Multi-wavelength holography is demonstrated with a H(2) Raman shifter that is pumped with an elliptically-polarized pulsed 532 nm beam to produce temporally coherent, intense, polarized output lines. Digital holograms of two-dimensional colored objects are recorded using Raman output lines at 630.4 nm (S(05), Red), 532 nm (Rayleigh, Green) and 435.7 nm (aS(10), Blue). Object reconstruction is done numerically via the convolution method and colored object recognition is achieved by multi-channel correlation of the Red, Green, and Blue reconstructions of the reference and the target object.

Two-color (two-photon) excitation fluorescence with two confocal beams and a Raman shifter

Abstract Two-color (two-photon) excitation fluorescence (2CF) with two confocal excitation beams is demonstrated with a Raman shifter as excitation light source. Coumarin 6H dye sample (peak absorption≈394 nm, peak fluorescence≈490 nm) is excited using the first two Stokes outputs (683, 954 nm, two-color excitation=398 nm) of a Raman shifter pumped by a 6.5 ns-pulsed 532 nm-Nd:YAG laser (repetition rate=10 Hz). The two Stokes pulses overlap for about 6 ns and two-color fluorescence is generated even with focusing objectives of low numerical apertures (NA

Pulsed full-color digital holography with a hydrogen Raman shifter

We demonstrate pulsed full-color digital holography with a hydrogen Raman shifter as a single source of highly directional multiwavelength light. For the primary (blue, green, red) color channels we utilize the first three Stokes beam outputs (415.9, 502.9, and 635.9 nm) of the shifter (gas pressure, 1.38 MPa) that is pumped by the 355-nm output of a pulsed Nd:YAG laser (5.4-ns pulse width, 10-Hz repetition rate). We have developed a simple beam-conditioning system to improve the transverse intensity distribution for the individual Stokes beams and to equalize their relative intensities. Full-color holographic imaging is demonstrated with transmitting and reflecting colored objects. Also, the optical noise characteristics of the reconstructed images are investigated.

MEASUREMENT OF WEAK TRANSMITTANCES BY STOCHASTIC RESONANCE

We use stochastic resonance to measure weak transmittance amplitudes that are below the instrumental detection limit. Gaussian noise is added to the subthreshold (chopped) transmittance signal T(t) before detection by a crossing detector that uses a dc reference signal B>0. Without noise, no measurement is possible because T(t)<B. A fourfold improvement has been obtained in the detection limit, permitting the measurement of amplitudes that are as small as 0.25B.

Temporal coherence control of Nd:YAG pumped Raman shifter

We investigate the temporal coherence properties of a Nd:YAG pumped hydrogen Raman shifter and report the control of the temporal coherence length z/sub c/ with hydrogen pressure for different input pump energies.

Amplification of Ultraviolet Femtosecond Pulse by a Micro-Pulling Down Method-Grown Ce:LiCAF Crystal in a Prismatic Cell-Type, Side-Pumping Configuration

We propose an efficient side-pumping scheme for ultraviolet (UV) femtosecond pulse amplification in micro-pulling-down (µPD) method-grown Ce:LiCAF using a prismatic cell-type configuration. By uniformly illuminating four sides of a 2-mm-diameter and 30-mm-length Brewster-cut, nearly as-grown crystal, the risk of damage is dramatically reduced. Without using a chirp pulse amplifier scheme, UV femtosecond pulse at 290 nm is amplified 4 times with no significant increase to its pulse duration and B-integral. Our results show that a laser-quality, Ce:LiCAF crystal, efficiently grown by the µPD method and pumped in a prismatic-cell type configuration paves new possibilities in providing high energy UV femtosecond pulses.

Position, orientation, and relative quantum yield ratio determination of fluorescent nanoemitters via combined laser scanning microscopy and polarization measurements

We present a universal method of determining the position, 3D orientation, and relative quantum yield ratio (RQYR) of fluorescent nanoemitters (ZnS coated CdSe quantum dots) in a glass slide by combining laser scanning microscopy (LSM) and polarization measurements. The quantum dots were located through LSM intensity maps using azimuthal, radial, and linear incident polarizations. LSM imaging was not sufficient to determine the orientation of the quantum dots due to the isotropic absorption dipole moment. The 3D orientation was obtained through polarization measurement. By combining LSM and polarization measurements, the RQYR of a single molecule was evaluated, allowing us to compare the quantum yield of the nanoemitters.

Post Deposition Heat Treatment Effects on Ceramic Superconducting Films Produced by Infrared Nd:YAG Pulsed Laser Deposition

Pulsed laser deposition (PLD) has become a potential method in fabricating highly quality superconducting thin films suitable for electronic applications such as in Josephson junctionbased electronics and in second generation coated conductors [11, 12, 14, 20, 23]. PLD of high Tc superconductors generally utilize excimer lasers in the ultraviolet (UV) range [6, 11] . However, excimer lasers use toxic gases such as Cl and F for excitation. In contrast, flash lamp pumped Nd:YAG laser can provide stable power and better beam profile [14, 20]. Nd: YAG lasers are also easy to operate and have low maintenance costs [2, 14, 20]. To date, the third harmonic (355 nm) and fourth harmonic (266 nm) of the Nd:YAG has been used to grow high quality high-Tc superconducting films [12, 14, 20].

Growth of Nd:YAG thin films on Silicon (111) substrate using femtosecond pulsed laser deposition

The influence of substrate heat treatment on the crystallinity and surface morphology of Nd:YAG thin films on Si (111) substrate grown by femtosecond pulsed laser depostion was investigated. A mode-locked 300 mW fs Ti:Sapphire laser was used to grow the Nd:YAG on the Si (111) substrate. The substrate temperature was varied from 300°C to 600°C while keeping the same deposition pressure to 10-6 mbar for 180 minutes. Post deposition was performed from 400°C to 600°C for 180 minutes. The SEM reveals granular surface with different microstructural features depending on the growth parameters. The XRD patterns show preferential growth at (521) direction after post heat treatment. However, higher temperature results to degradation of crystalline qualities of the films.

Nanosecond and femtosecond laser deposition of BiSrCaCuO on MgO

Pulsed laser deposition of BiSrCaCuO on MgO (100) using Q-switched Nd:YAG nanosecond laser operating at λ= 1064 nm (ns-PLD) and mode-locked Ti:Sa femtosecond laser at λ= 785 nm (fs-PLD) were performed. Rough surface with spheriodal morphology is the general microstructure of the deposited material from both nanosecond and femtosecond laser ablation. Femtosecond PLD resulted to granular morphology containing both BSCCO phase and rod-like Cu2O grains. Unlike ns-PLD, fs-PLD produced polycrystalline films even without heat treatment. These results indicate that two distinct ablation characteristic for ns-PLD and fs-PLD of BSCCO.