Self-focusing and self-defocusing by cascaded second-order effects in KTP.

Area of Science:

• Nonlinear optics
• Solid-state physics
• Materials science

Background:

• Cascaded second-order nonlinear processes (chi((2)):chi((2))) are essential for frequency conversion and all-optical switching.
• Potassium titanyl phosphate (KTP) is a widely used nonlinear optical material for various applications.
• Understanding nonlinear refractive effects is critical for designing efficient optical devices.

Purpose of the Study:

• To investigate the induced phase change and nonlinear refraction in KTP crystals.
• To experimentally verify theoretical predictions of nonlinear refractive index near phase matching.
• To quantify the effective nonlinear refractive index (n_eff^(2)) in KTP.

Main Methods:

• Utilizing the Z-scan technique to monitor induced phase changes.
• Employing a picosecond 1.06-microm-wavelength laser beam.
• Rotating the KTP crystal near the phase-matching angle.

Main Results:

• Observed a sign change in nonlinear refraction as the KTP crystal was rotated through the phase-matching angle.
• Measured a maximum small-signal effective nonlinear refractive index (n_eff^(2)) of approximately +/-2 x 10^-14 cm^2/W.
• Confirmed theoretical predictions regarding the sign change and magnitude of nonlinear refraction.

Conclusions:

• The cascaded chi((2)):chi((2)) process in KTP exhibits a sign-changing nonlinear refraction near phase matching.
• The Z-scan technique effectively probes nonlinear optical phenomena in KTP.
• The results provide valuable data for the development of advanced nonlinear optical devices.