Emittance of positron beams produced in intense laser plasma interaction

摘要

The first measurement of the emittance of intense laser-produced positron beams has been made. The emittance values were derived through measurements of positron beam divergence and source size for different peak positron energies under various laser conditions. For one of these laser conditions, we used a one dimensional pepper-pot technique to refine the emittance value. The laser-produced positrons have a geometric emittance between 100 and 500 mm·mrad, comparable to the positron sources used at existing accelerators. With 10~(10)-10~(12) positrons per bunch, this low emittance beam, which is quasi-monoenergetic in the energy range of 5-20 MeV, may be useful as an alternative positron source for future accelerators.