Abstract

Defects and dopants in glass are important for the observation of photoinduced second-harmonic generation (SHG) in fibers. We have recently observed that Tm in concentrations as low as 4 parts in 10⁶ in an aluminosilicate glass fiber enhances the induced second-harmonic signal by a factor of 104 over that of the undoped fiber.¹ We believe that the induced χ⁽²⁾ is associated with a space-charge field resulting from the generation and subsequent trapping of charge carriers that are generated by asymmetric photoionization² of the Tm³⁺ ions. On the basis of the optical absorption data for this glass, the photoionization process is expected to require at least three infrared (1064-nm) photons. The Tm³⁺ ions are relatively easily ionized because the ionization involves multiple steps: the Tm ion is first excited to the ¹G₁ state,³ which can be more easily photoionized than can the ³H₆ ground state.

© 1993 Optical Society of America