Nonlinear optical response of metal surfaces with adsorbed molecules

✍ Scribed by A. Salam; D. A. Micha

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 270 KB
• Volume: 75
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1999)75:4/5<429::aid-qua9>3.0.co;2-k

✦ Synopsis

A quantum mechanical theory describing the photodesorption dynamics of molecules bonded to metal surfaces and irradiated by pulsed laser light is presented. The physical system is separated into a primary region comprising the adsorbate and the bonding substrate atoms and a secondary region consisting of the remaining substrate. The two regions, which are strongly coupled, interact in a self-consistent manner via an electric dipole᎐electric dipole coupling. A density matrix approach, in which the density operator obeys the Liouville᎐von Neumann equation, is used to study the dynamics of photodesorption. An indirect desorption mechanism is considered and a local electromagnetic field, which induces electron᎐hole excitations in the metal, is introduced. The substrate response to femtosecond laser irradiation, including nonlinear effects of the laser electric-field strength, is investigated through solutions of the optical Bloch equations for the radiation field᎐substrate interaction and generalizes previous work for weak perturbing fields. An effective Hamiltonian which exhibits a nonlinear dependence on the field strength and includes the effects of dissipation is obtained. The theory developed Ž . is then parametrized using numerical values for the COrCu 001 adsorbate᎐substrate system and illustrated with model calculations. These show that the effective potential in the primary region is very sensitive to variations in the electric-field strength.