Abstract: A method of processing ions in a quadrupole rod set is provided, comprising a) establishing and maintaining a two-dimensional substantially quadrupole field having a quadrupole harmonic with amplitude A2 and a selected higher order harmonic with amplitude Am radially confining ions having Mathieu parameters a and q within a stability region defined in terms of the Mathieu parameters a and q; c) adding an auxiliary excitation field to transform the stability region into a plurality of smaller stability islands defined in terms of the Mathieu parameters a and q; and, d) adjusting the two-dimensional substantially quadrupole field to place ions within a selected range of mass-to-charge ratios within a selected stability island in the plurality of stability islands.

Abstract: A method of processing ions in a quadrupole rod set us provided. The method comprises a) establishing and maintaining a two-dimensional substantially quadrupole field for processing the ions, the field having a quadrupole harmonic with amplitude A2 and a selected higher order harmonic with amplitude Am wherein m is an integer greater than 2, and the magnitude of Am is greater than 0.

Abstract: A two-dimensional substantially quadrupole field is established and maintained to trap a selected group of ions. The field has a quadrupole harmonic with amplitude A2, and a higher order harmonic with an amplitude AN, AN being greater than 0.1%. The selected group of ions are trapped in the field. An oscillation frequency at a selected amplitude of excitation for the selected group of ions is determined. An excitation field at the selected amplitude of excitation is added to the two-dimensional substantially quadrupole field to deplete ions within a depletion peak having a low frequency side slightly above the oscillation frequency at the selected amplitude of excitation for the selected group of ions.

Abstract: An apparatus for measuring an absorption coefficient includes a first diffusive material, a second diffusive material inside the first diffusive material separated from the first diffusive material by a cavity, and a transparent material proximate to an inner surface of the second diffusive material that holds an absorptive material. First and second light detectors measure light intensities in the first and second diffusive materials respectively. An absorption coefficient for the absorptive material may be determined based on the first and second light intensities measured when the cavity is illuminated by a light source.

Abstract: An apparatus for measuring an absorption coefficient includes a first diffusive material, a second diffusive material inside the first diffusive material separated from the first diffusive material by a cavity, and a transparent material proximate to an inner surface of the second diffusive material that holds an absorptive material. First and second light detectors measure light intensities in the first and second diffusive materials respectively. An absorption coefficient for the absorptive material may be determined based on the first and second light intensities measured when the cavity is illuminated by a light source.

Abstract: An apparatus for measuring an absorption coefficient includes a first diffusive material, a second diffusive material inside the first diffusive material separated from the first diffusive material by a cavity, and a transparent material proximate to an inner surface of the second diffusive material that holds an absorptive material. First and second light detectors measure light intensities in the first and second diffusive materials cavity and the transparent material respectively. An absorption coefficient for the absorptive material may be determined based on the first and second light intensities measured when the cavity is illuminated by a light source.