High‐Order Above‐Threshold Ionization by Thermal Light

ABSTRACT Strong‐field ionization by thermal light is studied. Even though thermal light can be considered as completely classical stochastic light, it can also be treated as quantum light in the sense that it can be represented by a superposition of coherent states, similarly as has been done for the bright squeezed vacuum light, for example. Such a distribution over coherent states contains components with an intensity much higher than the average intensity of the thermal light. This increases the ionization probability by many orders of magnitude. For low intensities, in the multiphoton regime, the enhancement is by the factor of , with the multiphoton order of the process. This result is in agreement with an old experiment [ Phys. Rev. Lett . 32 (1974): 265] in which a similar enhancement factor appears if a multimode laser pulse is used instead of a single‐mode pulse. It is also shown that the plateau length in high‐order above‐threshold ionization by thermal light is extended by an order of magnitude in comparison with that of coherent laser light with the same average intensity.