Due to its large
NLO coefficients, broad angular broad angular,
spectral and temperature bandwidths as well as high mechanical
and chemically stability, Potassium Titanyl Phosphate (KTiOPO4
or KTP) is widely used in both commercial and military lasers
including laboratory and medical systems, range-finders, lidar,
optical communication, and industry systems. KTP's unique properties
make it superior in SHG and SFG, optical parametric generation,
electro-optic modulation, and optical waveguide.
Beijing Gospel OptoTech Co. (GOT)
has manufactured and supplied large quantities of high quality KTP
crystals for R&D, industrial and commercial customers. Our controlled
flux growth methods ensure a reliable supply of KTP crystals (45x67x82
mm3 transparent boules and 25x25x30 mm3 finished
devices) of consistent quality (top optical homogeneity, high
transmission and low scattering) and unbeatable price, 1-2 weeks
delivery.
Though KTP is commonly used in practices, the gray
track or photorefractive breakdown problem has puzzled users for a
very long period. So applications of KTP were extremely in the laser
systems of medium or low power density before. Through many years'
research on the growth of KTP in GOT, we developed one improved
technique to grow Super-KTPTM, which has up to ten
times higher gray track resistance comparing with common flux grown
KTP, for high power density applications. We began to supply the
Super-KTPTM commercial blocks in 1998 and the available
aperture of finished Super-KTPTM applied for
frequency doubling is up to 12x12 mm2. Any contact for
details or purchase is welcome.
Basic Properties
Density : 3.02
g/cm3
Crystal Structure
: Orthorhombic, point group mm2
Lattice Parameters
: a=6.404 A, b=10.616 A, c=12.814 A , Z=8
Mohs Hardness : »
5
Melting Point :
1172° C (Incongruent)
Curie Point : 936°
C
Specific Heat :
0.1643 cal/g° C (25° C)
Dielectric
Constant : e eff = 13
Absorption
Coefficient :
< 0.1%/cm @1.064 m m and < 1%/cm
0.532 m m
Thermal
Conductivity : 0.13 W/cm/° K
Electrical
Conductivity : 1.22x10-6s/cm (c-axis, 22° C, 2KHz)
Hygroscopic
Susceptibility : no
Optical and NLO Properties
Transparency Region : 0.35 m m ~ 4.5 m m
Nonlinear
Coefficients :
d31=2.54 pm/V, d32=4.35
pm/V, d33=16.9 pm/V
(@ 1.064 m m) d24=3.64
pm/V, d15=1.91 pm/V
deff(ll)» (d24-d15)sin2f
sin2q -(d15sin2f +d24cos2f
)sinq
(Where q and f are polar angles referring
to Z and X axis)
Refractive Indexes : nx ny
nz
1.740 1.746 1.830 (@ 1.064 m m)
1.778 1.789 1.888 (@ 0.532 m m)
Sellmeier Equations :
nx2 = 3.0065+0.03901/(l
2-0.04251)-0.01327l 2 (l
in m m )
ny2 = 3.0333+0.04154/(l
2-0.04547)-0.01408l 2
nz2 = 3.3134+0.05694/(l
2-0.05658)-0.01682l 2
Therm-optic Coefficients :
dnx/dT = 1.1x 10-5/°
C
dny/dT = 1.3x 10-5/°
C
dnz/dT = 1.6x 10-5/°
C
Electro-optic Coefficients
:
Low frequency High frequency (pm/V)
g 13
9.5 8.8
g 23
15.7 13.8
g 33
36.3 35.0
g 51
7.3 6.9
g 42
9.3 8.8
Damage Threshold :
> 500 MW/ cm2
at 1.064 m m. (10 ns, 10 Hz)
Main Applications of KTP Crystals
¨ Applications for
SHG and SFG of Nd:Laser
On the combination of its superior NLO properties (as
Table 1), KTP is the most commercial material applied for
intracavity and extracavity frequency doubler of Nd:YAG laser and
other Nd-doped laser, to get green outputs for versatile applications.
The very large temperature bandwidth is KTP's particular advantage to
maintain pulsed energy stability of the converted beam. KTP is also
being used successfully for intracavity mixing of 0.81m m diode and
1.06m m Nd:YAG laser to generate blue light and intracavity SHG of
Nd:YAG or Nd:YAP lasers at 1.3m m to produce red light. Moreover, with
the speedy development of diode-pumped Nd:lasers, KTP become more and
more important in the construction of the compact visible solid-state
lasers. Some typical results are listed as follows:
· More than 80%
conversion efficiency and 700mJ green laser were obtained with a 900mJ
injection-seeded Q-switch Nd:YAG laser by using extracavity KTP SHG;
· 20W green output
was generated from CW Nd: YAG laser with intracavity KTP;
· 3 W TEM00
mode-locked green laser was generated by intracavity SHG in a 5.3 W
mode-locked diode-pumped Nd:YAG laser;
· More than 200mW TEM00
green lasers are obtained from diode-pumped Nd:YAG and Nd:YVO4
lasers;
· 2.5mW green light was
obtained from 50mW LD pumped intracavity Nd: YVO4
mini-lasers with a 9mm long cavity.
Fig.1 illustrates Type II SHG
phase-matching angle of KTP in XY plane (0.9m m to 1.08m m). In XY
plane the slope ¶ (D λ)/¶ q is small. It
corresponds to quasi-angular noncritical phase matching, which ensures
the double advantage of a large acceptance angle and a small walk off.
Fig.2 shows Type II SHG phase-matching angle of KTP in XZ plane
(1.1m m to 3.4m m).
In XZ plane the slope ¶ (D θ)/¶
l is almost zero for wavelengths in the range 1.5 - 2.5 μm and this
corresponds to quasi-wavelength noncritical phase matching, which
ensures a large spectral acceptance. Wavelength noncritical phase
matching is highly desirable for frequency conversion of short pulses.
But KTP cut in YZ plane is seldom used to be phase-matched for SHG of
1m m to 3.45m m in practices due to its very low nonlinear
coefficients.
¨ Applications for
OPG , OPA and OPO
As an attractive material for OPG, OPA or OPO, KTP can
most usefully be pumped by a
Nd:lasers and their second harmonics, or any other
tunable output from visible (0.6 m m) to mid-IR (4.5 m m), such as Dye
laser (about 0.6 m m) and Ti:Sapphire Laser (about 0.7-1 m m). KTP's
OPO results in stable, continuous outputs of fs pulse of 108
Hz repetition rate and miliwatt average power levels in both signal
and idler output. Fig.3 shows .KTP OPO pumped by 532 nm tuning
curve in XZ Plane. KTP's OPO pumped by a 1.064 m m Nd:laser has
generated above 66% conversion efficiency for degenerately converting
to 2.12 m m.
The novel and effective application is the non-critical
phase-matched (NCPM) KTP OPO/OPA pumped by the tunable lasers. As
shown in Fig.4, the NCPM KTP OPO keeps the KTP crystal fixed in
X-axis and tunes pumping wavelength (0.7 m m to 1 m m), the output can
cover wavelength range from 1.04 m m to 1.45 m m (signal) and from
2.15 m m to 3.2 m m (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.
¨ Applications for
Optical Waveguides
With its low optical absorption and high damage
threshold, one new low optical loss waveguide fabricated by using
relatively simple ion-exchange process on KTP substrate, has created
new applications of integrated optics. Table 2 gives the
comparison of KTP with other optical waveguide materials.
Recently, type II SHG conversion efficiency of 20%/W/cm2
was achieved by balanced phase matching, in which the phase mismatch
from one section is balanced against a phase mismatch of opposite sign
from a second section. Furthermore, segmented KTP waveguide has been
applied to type I quasi-phase-matchable SHG of 0.76-0.96m m for
tunable Ti:Sapphire laser and directly doubled diode laser for
0.43-0.40m m output. Conversion efficiency in excess of 100%/W/cm2
have been obtained. The KTP crystal, which size is as large as 35x35x1
mm, with
-Z or both faces polished for waveguide applications,
are available in GOT. Other sizes are of course available
according to customers' requests.
Standard Specifications of KTP Crystals
Dimensional Tolerance : (W± 0.1mm)x(H ±
0.1mm)x(L+0.2/-0mm)
Wavefront Distortion : < l /4 @633 nm
Angle Tolerance : D q < ± 0.5° , D f < ± 0.5°
Scratch/Dig Code : 10/5 per MIL-O-13830A
Clear Aperture : > Central 90%
Flatness : l /10 @633 nm
Parallelism : < 20 arc seconds
Perpendicularity : < 5 arc minutes
Antireflection Coating : R < 0.1% @1.064m m, R < 0.2%
@0.532mm
Special Notes for KTP Crystals
· Other kinds of
coatings (AR or HR coatings) are available upon request.
· In order to meet the
rapid development of DPSS green laser market, GOT has large quantities
of KTP of standard dimensions (2x2x5 mm3, 3x3x5 mm3,
etc.) with dual-band AR coating for frequency doubling @1.064m m in
stock, and can deliver goods off-shelf.
· Standard apertures
for KTP waveguide substrates are 5x5,10x10, … 30x30mm2. One
surface of these waveguide substrates is polished to better than l /4
(with mount) and free from the surface defects when observed by a 50X
microscope, and the other face fine ground.
· Free samples of KTP
crystal are available from GOT for the purpose of long term technical
and business cooperation as well as the developments of new
applications. Qualified end users can also obtain free samples upon request.
· Our engineers will
provide specific designs and the latest technical information for KTP.
·
Special large discounts for industrial
customers! |
