The acoustics of a dental hard tissue laser (Er,Cr:YSGG laser, Waterlase MD, Biolase, USA) and a traditional dental high speed hand piece (Midwest®, Dentsply International, USA) were compared in vitro using a simple approach that can be easily adapted for in vivo studies. Thirty one extracted caries and restoration free primary anterior teeth were selected. These teeth were sectioned along a symmetry axis to give two identical halves for use in a split study. These halves were randomly assigned to either the laser (experimental) or the high speed (control) group. A miniature electret microphone was coupled to the sample using a polymer and used to collect the acoustic signal at the interface of the pulp chamber. This signal was captured periodically by a digitizing oscilloscope and multiple traces were stored for subsequent analysis. 2x1x1mm3 preparations were made according to manufacturers recommendations for the given method. Each cavity was prepared by the same clinician and calibration tests were performed to ensure consistency. The measurements indicated that the peak acoustic pressures as well as cumulative acoustic effects (due to duty cycle) were significantly higher (P<0.001, T-test) with the dental hand piece than with the dental laser. Our study suggests the need for further investigations into the neurological implications of acoustic effects in dental patient care such as pain studies.
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
cavity.
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