Why do intense laser fields produce fewer low-energy photons from electrons?

When ultraintense lasers collide with electrons, they emit single photons through nonlinear Compton scattering. The researchers found that simple plane-wave lasers produce finite photon yields, but special unipolar fields (no oscillating component) produce infinitely many low-energy photons—a divergence traced to increasingly long formation distances for softer radiation. For realistic focused beams, they calculated the quantum-to-classical corrections analytically.