Patent ID: 7816654

Claim:
An apparatus for irradiating a selected region of a target material in order to excite members of an excitable species contained within said selected region to a particular state of excitation to produce a measurable effect, comprising: an excitable species within said target material adapted to undergo excitation to said particular state of excitation when excited by brief pulses of radiation of a particular wavelength, to produce said measurable effect, and wherein, when said region is irradiated by longer pulses of said radiation of said particular wavelength, said measurable effect in response to said brief pulses is reduced; a source of radiation producing pulses sufficiently brief to excite said species, apparatus to split the radiation emanating from said source into a first beam of radiation and a second beam of radiation; a pulse stretcher in the path of said first beam adapted to increase the duration of pulses entering it; a pulse shaper in the path of said first beam, such that on emerging from said pulse shaper said first beam has a direction of propagation and a cross section perpendicular to said direction of propagation, and such that there is at least one minimum in the intensity of radiation of said beam in said cross section; and a beam combiner to combine first beam, after passing through both said pulse stretcher and said pulse shaper, with said second beam, to form a combined beam, directed to said material.