High-Brightness Wavelength-Beam-Combined Eyesafe Diode Laser Stacks
At 1450 nm, we have demonstrated 20-W wavelength-beam-combined output from a 25- element single bar (M<sup>2</sup> ~ 1.9 times 10), and 80-W cw from a 6-bar diode stack (M<sup>2</sup> ~ 36 times 68).
Coherent (phased array) and wavelength (spectral) beam combining compared (Invited Paper)
Significant progress has been recently reported on beam combining of arrays of fiber and semiconductor lasers using both coherent (phased array) and wavelength (spectral) techniques. The choice between these two classes of beam-combining techniques has implications for the degree of control required on the array elements and on the optical system that is using the beam-combined array. Coherent beam combining imposes more stringent requirements on array-element control (spectrum, phase, amplitude, and polarization) than wavelength combining. Also, wavelength-combined systems should degrade more gracefully than coherent systems and require fewer changes to optical systems as the number of elements is varied.
New Low-Profile Applicators for Local Heating of Tissues
A new type of low-profile applicator is described giving efficient power transfer to tissue with low leakage. It consists of a resonant element spaced from a ground plane by low-loss material having high relative permittivity and some relative permeability. This combination is covered by similar material which can be placed in direct contact with the tissue to be heated, or separated from it by a water bolus as required. Laboratory measurements using phantom materials show that these applicators are well matched and produce well defined and relatively uniform heating profiles. Applicators having maximum dimensions of 3-15 cm covering the frequency range 1000-100 MHz, respectively, are described. Penetration depths of at least 4 cm at 100-200 MHz are achieved. Tests on anesthetised pigs and some clinical assessment have confirmed the usefulness of this compact low-frequency type of applicator and have shown that performance compares favorably with that of other recently reported types. The design can be optimized for treatment of specific sites, and suitable choice of dimensions and electrical characteristics of the layer material allow the low-profile concept to be extended over a wide range of operating frequencies.