Related link:  KTP Crystal Components    

KTP Crystal Basic Properties

KTP Crystal Physical Properties

KTP Crystal Linear Optical Properties  

KTP Crystal Non-Linear Optical Properties

Applications for SHG and SFG of Nd:lasers

KTP is the most popular 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.

 

 

So far, 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 are obtained with a 900mJ injection-seeded Q-switched Nd:YAG laser.

 

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 instracavity-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 200mw TEM00 green outputs are available from LD pumped Nd:YVO4 and Nd:YAG lasers and 3W TEM00,mode-locked green laser was generated by intracavity SHG in a 5.3W mode-locked diode-laser pumped Nd:YAG laser. Moreover, 2.5mW green light is obtained from 50mW LD pumped and intracavity doubled Nd:YVO4 mini-lasers with a 9mm long cavity.

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

 

         

Applications for OPG, OPA and OPO

As an efficient OPO crystal pumped by the fundamental and second harmonics of an Nd:YAG or Nd:YLF Laser, KTP plays an important role in parametric sources for tunable output from visible (0.6μm) to mid IR (4.5μm). The phase-matching angles and effective NLO coefficient for OPO/OPA pumped at 532nm and 1064nm in XZ plane are shown as following figures. NCPM KTP OPO pumped by 1064 nm, the signal output is around eye safe wavelength, applications are found in eye-safe devices. The OPO/OPA in XY and YZ is seldom employed because of their low effective non-linear coefficients and other limitations.

 

       

KTP's OPO results in stable, continuous outputs of femtosecond pulse of 10 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 2120nm.

 

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:LiSrAIF (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 (0.7μm to 1μm), the output can cover the wavelength range from 1.04μm to 1.45μm (signal) and from 2.15μm to 3.2μm (idler). Due to the favourable NLO properties of NCPM KTP, as high as 45% conversion efficiency was obtained with narrow output bandwidth and good beam quality.

Quasi-Phase-Matched Waveguides

 

Recently, Type II SHG conversion efficiency of 20%/W/cm²  is 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 - 0.96μm for tunable Ti:Sapphire laser and directly doubled diode laser for 0.43 - 0.40μm output. Conversion efficiency in excess of 100%/W/cm² has been obtained.