Influence of color centers on the optical properties of KTP crystals and on the efficiency of the laser radiation frequency conversion in these crystals

Optical studies of laser-induced gray-tracking in KTP

“…Gray-tracking induced by a laser is classically studied on the basis of several types of experiments: visual observation of the darkening, observation of second-harmonic beam distortion during 1064-nm SHG [3], [4], optical transmission coefficient measurement by the beam which creates the damage [6] or by a probe beam during laser exposure [1], [2], [7], optical transmission or absorption spectra [2], [8]- [11], and electronspin-resonance (ESR) spectra [6], [8] measured before and after laser irradiation. From these experiments, some properties of the laser-induced gray-tracking have been determined: damage leads to a decrease in optical transmission over the entire visible range from 400 to 700 nm [2], [9], [11] with a magnitude which is a nonlinear function of the intensity of the laser beam creating the damage [2], [12]; the graytracking threshold, expressed as the laser peak intensity above which the damage is observed, is a decreasing exponential function of the -switch frequency [4]; a laser beam with a polarization parallel to the polar axis of KTP, i.e., the binary axis ( ), creates more damage than a beam polarized orthogonally to the axis [6], [9]; the time constant, usually a few minutes at room temperature, is dependent on the intensity of the laser beam until the level of gray-tracking reaches the Manuscript received July 6, 1998;revised November 6, 1998 asymptotic value [6], [7], [10], [12]. After the termination of laser exposure, the relaxation of the damage depends on the focusing conditions of the exposure beam, usually more than one year for strong focusing [4] and few hours for weak focusing [12] at room temperature.…”

Concept for power scaling second harmonic generation using a cascade of nonlinear crystals

“…2. In the simulations, experimentally measured efficiencies are used for 1 η and 2 η . Experimentally measured phase matching temperature widths and center temperatures are used to determine kL Δ as a function of temperature for each crystal.…”

“…However, not all nonlinear media are suited for high powers of the second harmonic (SH) because of adverse effects such as photochromism [2,3], photorefractivity [4] or thermal dephasing due to absorption [3,5,6].…”

High power red laser generation by second harmonic generation with GTR-KTP crystal

“…Potassium titanyl phosphate (KTiOPO 4 , KTP) is widely used for second harmonic generation (SHG) and optical parametric oscillations (OPOs) because of its high effective nonlinear coefficient, large acceptance angle, and large temperature bandwidth [1][2][3][4] . However, the laser induced damage gray-tracking problem limits the lifetime of KTP crystals for high-average-power SHG, especially for green laser generation [5][6][7] . The formation and absorption of Ti 3þ and Fe 3þ centers generated in KTP crystals give rise to the gray-tracking effect [8] .…”