|
Potassium
Titanyl Phosphate (KTiOPO4, KTP)
Potassium Titanyl Phosphate (KTiOPO4,
KTP) is the most commonly used in both
commercial and military lasers,
including laboratory and medical
systems, range-finders, lidars,
industry systems, and optical
communication.
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.
To overcome the gray track or
photorefractive breakdown
problem for KTP commonly used in
practices, AOTK has |
 |
developed one improved technique to grow
Super-KTP, which has up to 1.3-1.5 times
higher gray track resistance comparing with
common flux grown KTP, for high power density
laser systems applications. For more
information, please feel free to contact AOTK.
AOTK's KTP advanced properties
●
Large nonlinear optical coefficients
●
Broad temperature and spectral
bandwidth
●
Wide angular bandwidth and small
walk-off angle
●
High electro-optic coefficient and low
dielectric constant
●
Large figure of merit for an optical
waveguide modulator
●
Non-hygroscopic, chemically and
mechanically stable
Typical Applications of KTP
●
Frequency doubling (SHG) of Nd-doped
lasers for green/red output
●
Frequency mixing (SFM) of Nd laser and
diode laser for blue output
●
Parametric sources (OPG, OPA and OPO)
for 600 nm-4500 nm tunable output
●
E-O modulators, optical switches,
directional couplers
●
Optical waveguides for integrated NLO
and E-O devices
Basic Properties
1. Structual and Physical Properties
|
Crystal
Structure
|
Orthorhombic,
point group mm2
|
|
Lattice
Parameters
|
a
= 6.404Å, b = 10.616Å, c
= 12.814Å, Z = 8
|
|
Density
|
3.01
g/cm3
|
|
Mohs
Hardness
|
≈5
|
|
Melting
Point
|
~1172oC
|
|
Transition
Temperature
|
936oC
|
| Specific
Heat |
0.1643
cal/g°C |
|
Thermal
Conductivity
|
0.13
W/cm/°K
|
|
Electrical
Conductivity
|
3.5x10-8s/cm
(c-axis, 22°C,
1KHz)
|
|
Hygroscopic
Susceptibility
|
No
|
|
Dielectric
Constant
|
eeff
= 13.0, e11
= 11.6, e22
= 11.0, e33
= 15.4
|
|
Color
|
Colorless
|
2. Linear Optical Properties
|
Transparency
Region
|
350
- 4500 nm
|
|
Refractive
Indexes
at
1064
nm
at 532 nm
|
nx
= 1.7377,
ny = 1.7453,
nz = 1.8297
nx = 1.7780,
ny = 1.7886,
nz = 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 =
3.3134+0.05694/(λ2-0.05658)-0.01682λ2
|
|
Therm-Optic
Coefficients
|
dnx/dT
= 1.1 x 10-5/°C
dny/dT = 1.3 x 10-5/°C
dnz/dT = 1.6 x 10-5/°C
|
3. Nonlinear Optical Properties
|
Phase
Matching SHG Wavelength
|
497
- 1800nm
|
|
Nonlinear
Coefficients
|
d31
= 6.5 pm/v
d32 = 5.0 pm/v
d33 = 13.7pm/v
d24
= 7.6 pm/v
d15
= 6.1 pm/v
|
|
Effective
Nonlinearity Expressions
|
deff(II)
»
(d24 - d15)sin2fsin2q
- (d15sin2f
+ d24cos2f)sinq
|
|
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
r13
r23
r33
r51
r42
|
Low
frequency (pm/v)9.5
9.5
15.7
36.3
7.3
9.3
|
High
frequency (pm/v)
8.8
13.8
35.0
6.9
8.8
|
|
Optical
Damage
Threshold
|
>
450MW/cm2, (@
1064nm, 10ns, 10Hz)
|
Main Applications
I. SHG and SFG of Nd:Lasers
KTP exhibits the superior nonlinear and
electroptic properties. A combination of high
nonlinear coefficient, wide transparency
range, and broad angular as well as thermal
acceptances makes KTP very attractive for
intracavity and extracavity frequency doubler
of Nd:YAG laser and other Nd-doped laser
applications. The major NLO properties of KTP
for frequency-doubling of Nd:YAG or Nd:YVO4
lasers are listed as following table.
|
PM
Angle
|
θ
= 90°,
Φ = 23.5°;
where q and f are polar angles
referring to Z and X axis
|
|
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°)
|
KTP is also being applied successfully for
intracavity mixing of 808 nm diode and 1064 nm
Nd:YAG laser to generate blue light and
intracavity SHG of Nd:YAG or Nd:YAP lasers at
1300 nm to produce red light. With the
development of diode-pumped Nd:lasers, KTP
play more and more important role in the
construction of the compact visible
solid-state lasers. There are some typical
results listed as follows:
●
20W green output was generated from CW
Nd: YAG laser with intracavity KTP.
●
More than 80% conversion efficiency and
700mJ green laser were obtained with a 900mJ
injection
-seeded Q-switch Nd:YAG
laser with extracavity KTP SHG.
●
3W TEM00 mode-locked green
laser was generated by intracavity SHG in a
5.3W mode-locked diode
-pumped Nd:YAG laser.
●
More than 600mW TEM00 green
lasers are obtained from diode-pumped Nd:YAG
and Nd:YVO4 lasers.
●
2.8mW green light was obtained from
50mW LD pumped intracavity Nd: YVO4 mini-
lasers with a
8.5mm long cavity.
●
KTP also exhibits its powerful
applications for SHG and SFG laser with
wavelength 1000-3400 nm.
Fig.1 shows Type II SHG phase-matching angle
of KTP in X-Y plane. In X-Y plane the slope ¶(Dk)/¶q
is small. It corresponds to quasi-angular
noncritical phase matching, which ensures the
double advantage of a small walk off and a
large acceptance angle. Otherwise, in X-Z
plane the slope ¶(Dk)/¶l
is almost zero for wavelengths in the range
1.5-2.5 μm and the corresponds to
quasi-wavelength noncritical phase matching,
which ensures a large spectral acceptance (see
Fig 2). Wavelength noncritical phase matching
is highly desirable for frequency conversion
of short pulses. Fig.2 shows Type II SHG
phase-matching angle of KTP in X-Z plane (1.1-
3.4 mm).
KTP is seldom used to be phase-matched for SHG
of 1.0- 3.45 mm
in practices by cut in Y-Z plane, due to its
very low non-linear coefficients.
|
|
|
|
Fig.
1. Type II KTP SHG in X-Y Plane
|
Fig.
2. Type II KTP SHG in X-Z Plane
|
II. OPG, OPA and OPO
As a lasing material for OPG, OPA or OPO , KTP
can most usefully be pumped by the fundamental
and second harmonics of a Nd:lasers, or any
other source with intermediate wavelength,
such as a Dye laser (near 600 nm) and
Ti:Sapphire laser (near 700-1000 nm), in
parametric sources for tunable output from
visible (600 nm) to mid-IR (4500 nm). 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. KTP's OPO pumped by a 1064
nm Nd:laser has generated more than 66%
conversion efficiency for degenerately
converting range 1064-2120 nm. Fig.3 &
Fig. 4 show KTP OPO pumped by 532 nm &
1064 nm tuning curve in XZ Plane respectively.
|
|
|
|
Fig.3
KTP OPO Pumped by 532 nm
Tuning Curves in X-Z Plane
|
Fig.4
KTP OPO Pumped by 1064
nm
Tuning Curves in X-Z Plane
|
| The
new and effective application is the
non-critical phase-matched (NCPM) KTP
OPO/OPA pumped by the tunable lasers
(as shown in Fig.5). The output can
cover wavelength range from 1040 nm to
1450 mm (signal) and from 2150 nm to
3200 nm (idler), by fixed the NCPM KTP
crystal fixed in X-axis, and tunes
pumping wavelength (700 nm to 1000
nm). 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. |
|
III. Quasi-Phase-Matched Waveguide
On
low optical absorption and high damage
threshold, the low optical loss waveguide
fabricated by applying relatively simple
ion-exchange process on KTP substrate, has
created novel applications of integrated
optics. Following table shows the comparison
of KTP with other optical waveguide materials.
Recently, Type II SHG conversion efficiency of
above 20%/W/cm2 was obtained by balanced phase
matching, in which the phase mismatch from one
was balanced against a phase mismatch of
opposite sign from a second section.
Furthermore, segmented KTP waveguides have
been applied to type I quasi-phase-matchable
SHG of 760-960 nm for tunable Ti:Sapphire
laser and directly doubled diode laser for
400-430 nm output. Conversion efficiency in
excess of 100%/W/cm2 have been obtained.
As large as 35x35x1 mm KTP with Z-cut or both
surfaces polished for waveguide applications
can be provided by AOTK. Other sizes of course
available upon request.
Electro-Optic Waveguide Materials
|
Materials
|
n3γ/εeff(pm/V)
|
g
(pm/V)
|
εeff
(ε11ε33<,
/SUB>)1/2
|
n
|
|
KTP
|
17.3
|
35
|
13
|
1.86
|
|
KNbO3
|
9.2
|
25
|
30
|
2.17
|
|
LiNbO3
|
8.3
|
29
|
37
|
2.20
|
|
Ba2NaNb5O15
|
|
56
|
86
|
2.22
|
|
SBN(25-75)
|
5.1-0.14
|
56-1340
|
119-3400
|
2.22
|
|
GaAS
|
4.0
|
1.2
|
14
|
3.60
|
|
BaTiO3
|
1.0
|
28
|
373
|
2.36
|
IV. E-O Devices
KTP's unique NLO features and E-O and
dielectric properties make it extremely useful
to various E-O devices. Table gives the
comparison of KTP with those commonly used E-O
modulator materials.
Electro-Optic Modulator Materials
|
|
Phase
|
Amplitude
|
|
Materials
|
ε
|
|
r
pm/v
|
K
10-6/°C
|
n7r2/ε(pm/v)2
|
|
|
|
|
KTP
|
15.42
|
1.80
|
35.0
|
31
|
6130
|
27.0
|
11.7
|
3650
|
|
LiNbO3
|
27.9
|
2.20
|
28.8
|
82
|
7410
|
20.1
|
42
|
3500
|
|
KD*P
|
48.0
|
1.47
|
24.0
|
9
|
178
|
24.0
|
8
|
178
|
|
LiIO3
|
5.9
|
1.74
|
6.4
|
24
|
335
|
1.2
|
15
|
124
|
When these properties are combined with wide
optical bandwidth (>15GHz), low loss, high
damage threshold, thermal and mechanical
stability, KTP can be expected to replace a
considerable volume of LiNbO3
crystals as E-O modulators, especially for
mode-locking diode laser pumped Nd:YAG and
Nd:YLF lasers as well as Ti:Sapphire and
Cr:LiSrAlF6 laser.
Standard Specifications
|
Dimensional
Tolerance
|
(W
±
0.1mm) x (H ±
0.1mm) x (L +0.2/-0.1 mm)
|
|
Wavefront
Distortion
|
<
λ/8 @633 nm
|
|
Angle
Tolerance
|
Δθ
< ±
0.2°,
ΔΦ< ±
0.2°
|
|
Flatness
|
λ/10
@633 nm
|
|
Surface
Quality
|
10/5
Scratch/Dig per MIL-O-13830A
|
|
Parallelism
|
<
10
arc seconds
|
|
Perpendicularity
|
<
5 arc minutes
|
|
Clear
Aperture
|
>
90% central area
|
|
AR
Coating
|
R
< 0.1% @1064nm, R < 0.3%
@532nm per surface
|
|
Quality
Warranty Period
|
one
year under proper use
|
Standard Products
|
Part
No.
|
Dimension
|
Application
|
Coating
|
Type
|
|
KTPS203
|
2x2x3mm
|
SHG@1064nm
|
AR/HR
coating
|
II
|
|
KTPS205
|
2x2x5mm
|
SHG@1064nm
|
DBAR
coating
|
II
|
|
KTPS305
|
3x3x5mm
|
SHG@1064nm
|
DBAR
coating
|
II
|
|
KTPS310
|
3x3x10mm
|
SHG@1064nm
|
DBAR
coating
|
II
|
|
KTPS705
|
7x7x5mm
|
SHG@1064nm
|
DBAR
coating
|
II
|
|
KTPS805
|
8x8x5mm
|
SHG@1064nm
|
DBAR
coating
|
II
|
|
KTPS907
|
9x9x7mm
|
SHG@1064nm
|
DBAR
coating
|
II
|
|
KTPO720
|
7x7x20mm
|
OPO
for 1064nm pumped, 1570nm output
|
AR
coating
|
II
|
●
DBAR Coating: AR @ 1064nm & 532nm;
HR
Coating: AR @ 1064nm & HT @532nm;
AR
coatings: AR @ 1064nm & 1570nm
|
