Using advanced technique in crystal growth, 35x55x68mm3transparent KTP boule with flux method has been grown. As large as 15x15x20mm3KTP devices are fa/liicated. We provide KTP with:
|Crystal structure||Orthorhombic, space group Pna21,point group mm2|
|Cell parameters||a=6.404 Angstrom, b=10.616 Angstrom, c=12.814 Angstrom, Z=8|
|Melting point||1172° C incongruent|
|Curie point||936° C|
|Mohs hardness||» 5|
|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)|
|Phase matchable SHG range:||497 - 1800nm|
|Nonlinear optical coefficients:||
d31=6.5pm/v, d32=5pm/v, d33=13.7pm/v, d24=7.6pm/v, d15=6.1pm/v
deff(II) » (d24- d15)sin2f sin2q - (d15sin2f + d24cos2f )sinq
|For type II SHG of a Nd:YAG laser at 1064nm:||
PM angle: q =90° , j =23.3° Effective SHG coefficient: deff» 8.3xd36(KDP)
Angular acceptance: 20 mrad-cm Temperature acceptance: 25° C-cm
Spectral acceptance: 5.6 Angstrom -cm Walk-off angle: 4.5 mrad (0.26° )
Damage threshold: >450MW/cm2@1064nm, 10ns, 10Hz
|Electro-optic coefficients: r13 r23 r33 r51 r42||
Low frequency (pm/V) High frequency (pm/V)
9.5 8.8 15.7 13.8 36.3 35.0 7.3 6.9 9.3 8.8
|Transmitting range:||350 nm - 4500 nm|
|Refractive indices: 1064nm 532nm||nxnynz 1.7377 1.7453 1.8297 1.7780 1.7886 1.8887|
|Therm-optic coefficients:||dnx/dT=1.1x10-5/° C, dny/dT=1.3x10-5/° C, dnz/dT=1.6x10-5/° C|
|Absorption||a < 1% cm-1@1064nm and 532nm|
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. To date, extra- and intra-cavity frequency doubled Nd:lasers using KTP have become a preferred source of pumping visible dye lasers and tunable Ti:Sapphire lasers as well as their amplifiers. Applied to diode-pumped Nd:laser, KTP has provided the basis for the construction of compact visible solid state laser systems.
Recent advances in intracavity-doubled Nd:YAG and Nd:YVO4 lasers, have increased the demand for compact green lasers used in optical disk and laser printer. Over 100mW and 76mW TEM00 green outputs are available from LD pumped Nd:YAG and Nd:YVO4 lasers, respectively. Moreover, 2.5mW green light has derived from 50mW LD pumped and intracavity doubled Nd:YVO4 mini-lasers with a 9mm long cavity.
KTP has also shown its powerful applications in extracavity SHG with conversion efficiency exceeding 60%. The applications of KTP for intracavity mixing of 810nm diode and 1064nm Nd:YAG laser to generate blue light and intracavity SHG of Nd:YAG or Nd:YAP lasers at 1300nm to produce red light are also in progress.
As an efficient OPO crystal pumped by a Nd:laser and its second harmonics, KTP plays an important role for parametric sources for tunable output from visible (600nm) to mid-IR (4500nm). 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 output. KTP's OPO pumped by a 1064nm Nd:YAG laser has generated above 66% efficiency for degenerately converting to 2120nm.
We produce KTP crystals with gray track resistance up to ten times greater than typical flux grown KTP. This is possible due to advances in the controlled growth of KTP crystals, using proprietary modified fluxes and heat treatment. These HGTR KTP elements are suitable for high power density applications, where many other KTP elements would suffer from gray tracks or photorefractive breakdown.
IR (1064 nm) absorption growth under 10 KW/cm2 of green light (514 nm)
In the GRIIRA (Green Induced Infrared Absorption) test, an infrared laser beam passes through the KTP element.
The initial measurement (at time 0) is the infrared absorption of the crystal. After a few seconds, a green laser beam is allowed to go through the crystal as well. The green light causes an increase in the IR absorption of the crystal. This effect has been show to correlate with gray tracking in KTP crystals.
The above graph shows that the HGTR KTP elements have both a lower initial IR absorption, and are affected less by the green laser. Thus, the HGTR KTP is expected to have a higher gray track resistance than regular flux grown crystals or hydrothermally grown crystals.
Periodically Poled KTP is an entirely new type of non-linear material. It can be tailor- made for all non-linear applications within the transparency range of KTP, without the phase matching limitations of bulk KTP. Its effective non linear coefficient is about three times larger than that of bulk KTP. We offer PPKTP in large production quantities, as well as small quantities for development work.
KTP is a ferroelectric crystal. In the classic use of bulk KTP, it is important to have a single domain crystal. In PPKTP, a periodic domain structure is artificially induced in the crystal. The exact spacing of these periods depends on the application, and ranges from a few microns to tens of microns. The period is induced in the direction in the crystal that has the highest non-linear coefficient, as opposed to the bulk crystal, where the direction is dictated by the phase matching constraints. Some degree of crystal temperature control is necessary in using PPKTP.
PPKTP is produced in a multi-step process. An electrode of the desired structure is deposited on the surface of a KTP wafer, using micro lithographic techniques. An electric field is applied to the crystal under carefully controlled conditions, thus inducing the desired change in domain structure. The resulting KTP is then tested, cut into appropriate pieces, polished and coated. The technique lends itself to mass production at a reasonable cost.
PPKTP is available in standard elements for some common applications, such as second harmonic generation of 1064 nm and 946 nm. It can also be specially designed and manufactured for specific applications.
Test Conditions: Crystal length = 10 mm, t= 10 ns, Pulse frequency = 2 kHz