Self-dual Spectral Singularities and Coherent Perfect Absorbing Lasers   without PT-symmetry
  A PT-symmetric optically active medium that lases at the threshold gain also acts as a complete perfect absorber at the laser wavelength. This is because spectral singularities of PT-symmetric complex potentials are always accompanied by their time-reversal dual. We investigate the significance of PT-symmetry for the appearance of these self-dual spectral singularities. In particular, using a realistic optical system we show that self-dual spectral singularities can emerge also for non-PT-symmetric configurations. This signifies the existence of non-PT-symmetric CPA-lasers. 
Ali Mostafazadeh
quant-ph hep-th math-ph math.MP physics.optics