The current effort reports on the spectroscopic properties (absorption, emission and fluorescence lifetime) as a function
of varying Erbium concentration in Y2O3. Results show a non-linear behavior in the fluorescence lifetimes and the
radiative-emission intensities for the 4I11/2 and the 4I13/2 energy levels.
A novel method is presented for beam shaping far field intensity distributions using coherently combined fiber
arrays. Traditionally, coherent arrays have been composed of linearly polarized elements having their polarization
vector along a common axis. In this novel method, the fibers are arranged uniformly on the perimeter of a circle,
and the linearly polarized beams are oriented with their polarization vectors arranged in a cylindrical fashion
such that each subsequent vector is rotated by 2π/N where N is the number of elements on the circle. The
elements each have the same Gaussian intensity distribution and power. The ensemble yields a far field intensity
pattern that is a good approximation to a cylindrical vector (CV) beam which is characterized by a nonuniform
polarization distribution and a null in the center of the beam. These synthetically created CV beams, or discrete
cylindrical vector (DCV) beams, can be represented in a closed form solution to predict the far field intensity
distributions. This solution is shown to agree with experimental results where several values of N, the number of
elements, were tested. In addition, some more complex geometries such as nested geometries, fractal geometries,
and some nonuniform geometries have been simulated, all of which also have a central null in the beam and
have a nonuniform polarization distribution. These results are in contrast to linearly polarized beams, where
the intensity peaks on axis, and from traditional cylindrical vector beams, which are generated by a single laser
Room temperature, multi-wavelength operation in 2% doped Er:YAlO3 under flashlamp excitation is reported. Lasing
occurred predominantly at 1.6625 &mgr;m and 1.6725 &mgr;m with the emission at the two wavelengths being orthogonally
polarized. The use and orientation of an intracavity polarizer dictates the lasing wavelength in the laser. Temporal
analysis of the two laser wavelengths shows that the onset of lasing at the two wavelengths is separated by ~14 &mgr;s with
lasing at the 1.6625 &mgr;m wavelength occurring first. The 14 &mgr;s delay suggests that the 1.6625 &mgr;m emission is due to
lasing on the 4S3/2 →4I9/2 transition (4-level), while the 1.6725 &mgr;m emission is due to cascaded lasing on the 4I13/2 →4I15/2
transition (3-level). Using a rotating mirror Q-switch, ~80 ns pulses at 10 mJ/pulse were generated. The wavelength of
the Q-switched emission was determined to be at 1.6625 &mgr;m.
The development of an alumina-rich cobalt-doped spinel saturable absorber for the passive q-switching of 1530-1555 nm lasing is reported1. This optimized composition results in crystals with excellent dopant uniformity that are highly manufacturable. The crystal growth and materials characterization are described as well as initial passive qswitch testing of the material. The single crystals grown and investigated crystallized in the Fd3m space group and have the formula Mg1-xCoxAlyOz where x is greater than 0 and less than 1, y is greater than 2 and less than about 8, and z is between about 4 and 13. Comparison data of stoichiometric spinel MgAl2O4 and alumina-rich non-stoichiometric spinel MgAl6O10 are presented. The spinel lattice is comprised of octahedral and tetrahedral cationic sites, and in the alumina-rich spinel essentially all of the magnesium and cobalt occupy tetrahedral sites. The alumina-rich cobalt-doped spinel studied exhibited uniform cobalt-dopant distribution throughout the crystal and desirable mechanical and physical properties. Q-switched pulses were produced using the alumina-rich Co2+:MgAl6O10 saturable absorber in a 980 nm diode-pumped Yb:Er:glass solid-state-laser operating at 1543 nm. The q-switching established employed the 4T1 absorption band of the Co2+: MgAl6O10 and with quasi-CW pumping, pulsewidths greater than 20 ns, pulse energies of greater than 250 mJ, and free-running pulse repetition frequencies (PRFs) up to 1.2 kHz were demonstrated.
In this paper, pulsed operation of the 980 nm diode-pumped Yb:Er:glass solid-state-laser operating at 1543 nm using Co:Spinel saturable absorber is described. The Yb:Er:glass gain medium was end-pumped using a 10 W fiber-coupled 980 nm laser diode. Passively q-switched laser operation was accomplished for both CW and quasi-CW operations. Up to 2 mm thick uncoated Co:Spinel samples were used for our tests. With quasi-CW pumping, pulsewidths greater than 20 ns, pulse energies of greater than 250 μJ and free-running PRFs up to 1.2 kHz have been demonstrated. So far, up to 3 % optical-to-optical efficiency has been achieved with uncoated q-switch materials. Currently, this laser is being developed for pumping a long-wave IR (8-12 μm) optical parametric oscillator for use in spectrapolarimetric applications.
Studies have shown that a water spray may augment the laser ablation rate of dental hard tissues in addition to reducing heat accumulation. However, the mechanism of augmentation is controversial and poorly understood. The influence of an optically thick applied water layer on the ablation rate was investigated at wavelengths in which water is a primary absorber and the magnitude of absorption varies markedly. Water was manually applied with a pipette and troughs were cut in enamel blocks using a laser scanning system. Q- switched and free running Er:YSGG and Er:YAG, free running Ho:YAG and 9.6 micrometers TEA CO2 laser systems were investigated. The addition of water increased the rate of ablation and produced a more desirable surface morphology during enamel ablation with all the erbium systems. Ablation was markedly more efficient for the Q-switched erbium lasers than for the longer free-running laser systems when a water layer was added. Although, the addition of a thick water layer reduced the rate of ablation during CO2 laser ablation, the addition of the water removed undesirable deposits of non-apatite mineral phases from the crater surface. There was extensive peripheral damage after irradiation with the Ho:YAG laser with and without added water without effective ablation of enamel. The results of this study suggest that water augments the ablation of dental enamel by aiding in the removal of loosely attached deposits of non-apatite mineral phase from the crater surface, thus producing a more desirable crater surface morphology. The non-apatite mineral phase interfere with subsequent laser pulses during erbium laser irradiation reducing the rate of ablation and their removal aids in maintaining efficient ablation during multiple pulses irradiation.
Recently, erbium-based lasers engineered to emit at the shorter 2.69 - 2.71 micrometers transitions have demonstrated desirable therapeutic results with tolerable thermal tissue damage in dental and ophthalmic applications. Moreover, transmission of the 2.69 um radiation through an ordinary low-OH silica fiber with acceptably low losses has been achieved. In addition to medical and dental applications, the 2.62 and 2.69-micrometers radiation from CrTmEr:YAG (CTE:YAG) is also suitable as a pump source for nonlinear materials in order to generate radiation in the 3 - 14 micrometers region. In the present work, stable and efficient room-temperature operation of a flashlamp-pumped CTE:YAG laser operating at the 2.69 micrometers transition is reported. The optimization of the dopant concentrations, the spectral characteristics of the resonator optics, and the AR coatings on the laser rod have resulted in a laser that emits radiation only at (lambda) equals 2.69 micrometers for incident pump energies as high as 250 J/pulse. In the free running mode, output energies approaching 1 J/pulse at a repetition rate of 4 - 6 Hz, and slope efficiencies of approximately 0.6% have been achieved. In the Q-switched regime, output energies of 35 - 50 mJ in the fundamental TEMoo mode have also been achieved.
The purpose of this study was to evaluate the suitability of Q-switched Er:YAG radiation with a pulse duration of approximately 150 ns for caries ablation in dental enamel and dentin. The rate and efficiency of ablation were determined at various laser fluences via perforation of enamel and dentin thin slabs. Peripheral thermal and acoustic damage was evaluated using optical and electron microscopy. Enamel and dentin were ablated with extremely high precision without peripheral thermal damage using these short laser pulses. However, mechanical damage resulted from stress transients produced during the ablative process which caused fracture s in dentin and enamel on the back side of the perforated tissue samples. The thickness of the layer of spallated dentin increased linearly with deposited energy consistent with proposed models. The possibility of acoustic-mechanical damage may limit the maximum single pulse energy that may be deposited when using short pulsed Er:YAG lasers for hard tissue use. This work was supported by NIH/NIDR Grant R29DE12091.
The suitability of CTE:YAG laser radiation was investigated for caries preventive laser treatments and caries ablation. Although, CTE:YAG laser radiation at 2.69 micrometer is less highly absorbed by dental hard tissues than other erbium laser wavelengths, namely 2.79 and 2.94 micrometer, it can readily be transmitted through a conventional low hydroxyl fiber with minimal loss. These studies show that reasonable ablation rates and efficiencies are obtainable with both free running (200 microseconds) and Q-switched (100 ns) laser pulses on both dentin and enamel with the application of a relatively thick layer of water to the tissue surface. The water served to remove tissue char and debris from the ablation site leaving a clean crater. However, mechanical forces produced during the energetic ablative process resulted in peripheral mechanical damage to the tissue. Surface dissolution studies on enamel indicated that CTE:YAG radiation inhibited surface dissolution by organic acid by 60 - 70% compared to unirradiated controls, albeit, at fluences an order of magnitude higher than those required for CO2 laser radiation. This layer system may be suitable for dental hard tissue applications if mechanical damage can be mitigated. This work was supported by NIH/NIDR Grants R29DE12091 and R01DE09958.