Newlight's KTP features
Large
nonlinear optical coefficients |
Wide
angular bandwidth and small walk-off angle
|
Broad
temperature and spectral bandwidth |
High electro-optic
coefficient and low dielectric constant
|
Large figure of merit
|
Nonhydroscopic,
chemically and mechanically stable |
High thermal conductivity
|
Extremely low cost
compared to BBO
and LBO |
KTP
is a positive biaxial crystal, with the principal axes X, Y, and Z (nz>ny>nx
) parallel to the crystallographic axes a, b, and c, respectively.
Structural and
Physical Properties
Crystal
Structure |
Orthorhombic,
Space group Pna21, Point group mm2 |
Cell Parameters |
a=6.404Å, b=10.616Å, c=12.814Å, Z=8
|
Melting
Point |
1172oC in congruent
|
Curie Point |
936oC |
Mohs Hardness |
~ 5
|
Density |
3.01 g/cm3
|
Color |
Colorless
|
Hygroscopic
Susceptibility
|
No
|
Specific
Heat |
0.687 J/g/K |
Thermal
Conductivity |
2 W/m/K
|
Electrical
Conductivity
|
3.5x10-8 s/cm (c-axis,
@22oC, 1KHz)
|
Linear
Optical Properties:
Transmitting
Range |
350 nm -
3500 nm |
Refractive
Indices
1064nm
532nm |
nx ny nz
1.7377 1.7453 1.8297
1.7780 1.7886 1.8887
|
Sellmeier Equations
(λ in µm) |
nx2=3.0065+0.03901/(λ2-0.04251)-0.01327λ2
ny2=3.0333+0.04154/(λ2-0.04547)-0.01408λ2
nz2=3.0065+0.05694/(λ2-0.05658)-0.01682λ2
|
Thermo-optic
Coefficients |
dnx/dT=1.1x10-5/oC, dny/dT=1.3x10-5/oC
dnz/dT=1.6x10-5/oC
|
Absorption
Coefficient |
α < 1% cm-1 @1064nm and
532nm |
Nonlinear Optical
Properties:
Phase-matchable SHG
Range |
994 - 3600nm |
Nonlinear
Optical Coefficients |
d31=1.95pm/v, d32=3.9pm/v,
d33=15.3pm/v,d24=3.9pm/v,
d15=1.95pm/v
|
Effective Nonlinearity Expressions
|
deff(II)= (d24-d15)sin2φsin2θ-(d15sin2φ+ d24cos2φ)sinθ
|
For type II SHG of
a Nd:YAG Laser at 1064nm
|
PM angle:
θ=90°,
φ=23.5°
Effective SHG coefficient: deff=8.3xd36(KDP)
Angular acceptance: 20 mrad-cm
Temperature acceptance: 25°C-cm
Spectral acceptance: 5.6 Å -cm
Walk-off angle: 4.5 mrad (0.26°) |
Electro-optic
Coefficients |
Low frequency (pm/V) |
High frequency
(pm/V) |
r13
|
9.5 |
8.8 |
r23
|
15.7 |
13.8 |
r33
|
36.3 |
35.0 |
r51
|
7.3 |
6.9 |
r42
|
9.3 |
8.8 |
Dielectric
Constant |
εeff=13
|
Application
examples:
SHG and SFG of
Nd:lasers
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.
PM Angle |
θ=90o,
φ=23.5o |
Effective SHG Coefficient |
deff = 8.3xd36(KDP)
|
Angular Acceptance |
20 mrad-cm |
Temperature Acceptance |
25oC-cm
|
Spectral Acceptance |
5.6 Å-cm. |
Walk-off angle |
4.5mrad (0.26o) |
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,
a conversion efficiency of over 80% and 700mJ green laser were obtained with a 900 mJ
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 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.
KTP is also a powerful crystal for
SHG and SFG of laser with wavelength from about 1um to 3.4um. The SHG
phase-matching angle and effective SHG coefficients (deff) of KTP in XY plane (0.9
um to 1.08 um) and XZ plane (1.1 um to 3.3 um) are showed as the
figures. Although KTP cut in YZ plane can be phase-matched for SHG of 1 um to 3.45
um, it is seldom used in practice because of the low deff.
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 (0.6um) to mid-IR
(4.5um).
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. 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
um to 1 um), the output can cover the wavelength range from 1.04mm to 1.45 mm (signal) and from 2.15
um to 3.2 um (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 0.76-0.96um for tunable Ti:Sapphire
laser and directly doubled diode laser for 0.43-0.40um output. Conversion
efficiency in excess of 100%/W/cm2 has been obtained.
NCPM KTP for OPO
The recently developed new application is the
non-critical phase-matched (NCPM) KTP OPO/OPA. The NCPM KTP OPO keeps the KTP
crystal fixed in X-axis and tunes the pumping wavelength. With a 1064nm pumping
source, the output will be at 1.57um (signal) and 3.3 um (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.