Double‐Beam Linear Dichroism Investigation of the Two‐Photon Absorption in InSb

A double‐beam linear dichroism method is developed to determine the amplitude of the polarization dependent part (β ∽ ) of the total TPA constant (β 12 ) in crystals. This method allows to separate two‐photon processes via virtual states from attendant effects. Two‐photon absorption in some n‐type InSb samples is investigated by using CO 2 laser pulse radiation (λ = 10.6 μm) at T = 300 K. The electron concentration dependence of β ∽ is evidenced and explained by the increase of the conduction band population (Burstein‐Moss effect in the case of TPA). The results are in a good agreement with the theory used. In addition a double‐beam TPA constant β 12 as well as a single beam TPA constant β are determined by using the measured value of β ∽ and the theoretical relation between β l2 , β, and β ∽ .