• Quadratic medium yields two-dimensional spatial solitons

    Strong nonlinear coupling between fundamental and harmonic fields in a quadratic medium can produce two-dimensional spatial solitons, report researchers from the Center for Research in Electro-Optics and Lasers (CREOL, Orlando, FL) led by William Torruellas. In type II second-harmonic generation (SHG), two input fields with frequency w interact in a nonlinear medium to form a second-harmonic of frequency 2w. Normally, natural birefringence causes spatial displacement or `walk-off` of the interac
    Sept. 1, 1995
    2 min read

    Quadratic medium yields two-dimensional spatial solitons

    Strong nonlinear coupling between fundamental and harmonic fields in a quadratic medium can produce two-dimensional spatial solitons, report researchers from the Center for Research in Electro-Optics and Lasers (CREOL, Orlando, FL) led by William Torruellas. In type II second-harmonic generation (SHG), two input fields with frequency w interact in a nonlinear medium to form a second-harmonic of frequency 2w. Normally, natural birefringence causes spatial displacement or `walk-off` of the interacting beams, and SHG efficiency is saturated by diffraction. When the three fields involved in type II SHG are nearly phase-matched above a threshold power in potassium titanyl phosphate (KTP), however, strong nonlinear coupling compensates for diffraction and walk-off, spatially locking the interacting fields.

    A flashlamp-pumped Nd:YAG laser was passively modelocked and Q-switched to produce 15-ps Gaussian pulses at 1.064 µm. An extracavity electro-optic pulse selector allowed individual pulses to be focused onto the 1-cm-long KT¥crystal (JTT International, Orlando, FL). Beyond a threshold power of 10 GW/cm2, self-focusing induced by second-order interaction strictly compensated for diffraction and walk-off of all three fields involved. The beams were trapped into spatial soliton-like beams, with an output beam waist of 12.5 µm. To date, the only other method of producing stable two-dimensional spatial solitons in a condensed media is via the photorefractive effect (see p. 40).

    Sign up for Laser Focus World Newsletters
    Get the latest news and updates.

    Voice Your Opinion!

    To join the conversation, and become an exclusive member of Laser Focus World, create an account today!