i) KTP is the most commonly used material for frequency doubling of Nd:YAG lasers and other Nd-doped lasers, particularly at the low or medium power density.

The following Table lists the major NLO properties of KTP for frequency-doubling of Nd:YAG laser.

To date, extra- and intra-cavity frequency doubled Nd:lasers using KTP have become a preferred green laser source for many R&D, medical, industrial and commercial applications. By using extracavity KTP SHG, over 80% conversion efficiency and 700mJ green laser were obtained with a 900 mJ injection-seeded Q-switched Nd:YAG laser.

ii)Applied to diode-pumped Nd:laser, KTP is a basic NLO crystal for the construction of compact visible solid state laser systems. Recent advances in intracavity-doubled Nd:YVO4 and Nd:YAG lasers have increased the demand for compact green lasers used in display, construction, optical disk and laser printer. Over 200 mw TEM00 green outputs are available from LD pumped Nd:YVO4 and Nd:YAG lasers and 3 W TEM00, mode-locked green laser was generated by intracavity SHG in a 5.3 W mode-locked diode-laser pumped Nd:YAG laser. Moreover, 2.5mW green light was obtained from 50mW LD pumped and intracavity doubled Nd:YVO4 mini-lasers with a 9mm long cavity.

iii)KTP is also a powerful crystal for SHG and SFG of laser with wavelength from about 1mm to 3.4 mm. The SHG phase-matching angle and effective SHG coefficients (deff) of KTP in XY plane (0.9 mm to 1.08 mm) and XZ plane (1.1 mm to 3.3 mm) are showed as the figtures. Although KTP cut in YZ plane can be phase-matched for SHG of 1 mm to 3.45 mm, it is seldom used in practices because of the low deff.

iiii)OPG, OPA and OPO
As an efficient OPO crystal pumped by the fundamental and second harmonics of a Nd:YAG or Nd:YLF laser, KTP plays an important role in parametric sources for tunable output from visible (0.6mm) to mid-IR (4.5mm). The phase-matching angles and effective NLO coefficient for OPO/OPA pumped at 532 nm and 1064 nm in XZ plane are showed as following figures. NCPM KTP OPO pumped by 1064nm, the signal output is around eye safe wavelength, find applications in eye-safe devices. The OPO/OPA in XY and YZ is seldom employed because of their low effective nonlinear coefficients and other limitation.
KTP's OPO results in stable, continuous outputs of femtosecond pulse of 108 Hz repetition rate and miliwatt average power levels in both signal and idler outputs. KTP's OPO pumped by a 1064nm Nd:laser has generated above 66% conversion efficiency for degenerate conversion from 1064 to 2120 nm.
The recently developed new application is the non-critical phase-matched (NCPM) KTP OPO/OPA pumped by the tunable lasers such as Ti:Sapphire, Alexandrite and Cr:LiSrAlF6 (see right figure). The NCPM KTP OPO keeps the KTP crystal fixed in X-axis and tunes the pumping wavelength. If a tunable Ti:Sapphire laser is used as a pumping source (0.7 mm to 1 mm), the output can cover the wavelength range from 1.04mm to 1.45 mm (signal) and from 2.15 mm to 3.2 mm (idler). Due to the favorable NLO properties of NCPM KTP, as high as 45% conversion efficiency was obtained with narrow output bandwidth and good beam quality.
Quasi-Phase-Matched Waveguide
Recently, type II SHG conversion efficiency of 20%/W/cm2 was achieved by quasi-phase matched waveguide doubler, in which the phase mismatch from one section is balanced against a phase mismatch of the opposite sign from a second section. Furthermore, segmented KTP waveguides have been applied to type I quasi-phase-matchable SHG of 0.76-0.96mm for tunable Ti:Sapphire laser and directly doubled diode laser for 0.43-0.40m output. Conversion efficiency in excess of 100%/W/cm2 has been obtained.