Abstract: A chemical mechanical polishing apparatus has a platen to support a polishing pad, the platen having a recess, a carrier head to hold a surface of a substrate against the polishing pad and comprising a retaining ring to retain the substrate below the carrier head, a motor to generate relative motion between the platen and the carrier head so as to polish the substrate, an in-situ acoustic monitoring system comprising an acoustic sensor arranged in the recess that receives acoustic energy from friction between the substrate and the polishing pad and from friction between the retaining ring and the polishing pad, and a controller configured to generate a value for a carrier head status parameter based on received acoustic signals from the in-situ acoustic monitoring system, and change or polishing parameter or generate an alert based on the carrier head status parameter.

Abstract: An IAU laser is stabilized to reduce intensity fluctuations. The laser comprises an IAU gain medium disposed in an optical resonance cavity and a multiphoton absorbing medium disposed in the cavity to reduce intensity fluctuations. A pump source to excite the gain medium is coupled to the cavity. In operation, the multiphoton absorbing material absorbs primarily at high intensity levels, effectively increasing the loss at high intensities. In an advantageous embodiment, the active medium comprises erbium-doped glass and the multiphoton absorber comprises a body of semiconductor exhibiting two-photon absorption at the emission wavelength.