Nonlinearities, Coherence and Dephasing in Layered GaSe and in CdSe Surface Layer

The fundamental requirement for useful optical switching devices, fast switching at low power, is not easily achieved. Low switching powers, can be obtained by making use of the strong enhancement of the nonlinear optical coefficients near electronic resonances. On the other hand, the creation of real excitations in the material tends to limit the response time to the lifetime of the electronic excitations. For direct gap semiconductors, carrier lifetimes are in the nanosecond or subnanosecond range, which is not satifactory for extensive use in all optical switching devices.1