- KTP has a combination of properties that make it unique for frequency-doubling Nd:YAG lasers and other Nd-doped systems emitting near 1064 nm;
- KTP is the preferred doubling crystal when the available peak power is limited (because of it large nonlinear coefficients combined with low absorption and wide acceptance angle);
- The unusually large temperature bandwidth of KTP is particularly advantageous for maintaining pulsed energy stability of the converted beam.
- The temperature bandwidth of KTP, combined with relatively good thermal properties, is exceptional for doubling high average-power-cw or quasi-cw beams.
- KTP is much less susceptible to bulk damage than, e.g., MgO:LiNbO3 at relatively high average-power levels. This property, combined with a low absorption loss at 1 mkm, renders KTP as a prime choice for all intracavity frequency-doubling applications.
Nonlinear-optical coefficients, [pm/V] |
d31 = 6.5 d32 = 5.0 d33 = 13.7 d24 = 7.6 d15 = 6.1 |
Temperature bandwidth, [°C cm] |
25 |
Angular bandwidth, [mrad cm] |
15 - 68 |
Spectral bandwidth, [A cm] |
5.6 |
Walkoff, [mrad] |
1 |
Temperature coefficient of refractive index, [°C-1] |
Dnx = 1.1 x 10-5 Dny = 1.3 x 10-5 Dnz = 1.6 x 10-5 |
Transmission range, [nm] |
350 - 4500 |
Optical absorption, [%/cm] |
< 0.6 at 1064 nm
< 2 at 532 nm |
Thermal expansion coefficients, [°C-1] |
a1 = 11 x 10-6 a2 = 9 x 10-6 a3 = 0.6 x 10-6 |
Thermal conductivity, [W/cm °C] |
k1 = 2.0 x 10-2 k2 = 3.0 x 10-2 k3 = 3.3 x 10-2 |
Pyroelectric coefficient,
[nC/cm2 °C] |
7
|
Specific heat, [cal/g °C] |
0.174 |
|
|
At present KTP with its superior features is well known as a perfectly suitable crystal for obtaining green light.
- Mode-locked systems emitting picosecond green pulses with > 2 W of average power, with or without pulse-compression techniques, for synchronously or hybridly pumping other laser sources in order to generate femtosecond pulses.
- In purely CW systems, intracavity frequency-doubled Nd:YAG lasers deliver as much as 10 W of green power and have successfully replaced the Ar-ion laser as cw pump source for tunable dye lasers used in ophthalmology.
- CW-pumped, intracavity-doubled, and Q-switched Nd:YAG lasers reliably generate in excess of 20 W green output; these systems, which permit efficient production of high average-power UV beams (by frequency doubling the green output), are now routinely used for general laser surgery.
- Efficient intracavity-doubling of flash-lamp-pumped systems with KTP has led to the production of > 10 mJ green pulses in a single transverse mode at a 10 Hz repetition rate. In another pulsed configuration 50% extracavity doubling efficiency has led to the generation of approximately 200 mJ in 120-mks green pulses without optical damage to the doubling crystal.
- At the low end of power spectrum, there is an increasing interest in miniature green solid-state laser sources for a variety of applications. In this category intracavity doubling of diode-pumped Nd:YAG and Nd:YVO4 lasers with 3-7-mm long KTP crystal have resulted in >10 mW of green power for only 200 mW of optical pump power (corresponding to 1 W of electrical power).
The overall electrical efficiency of this green laser approaches 1% ( for comparison, an air-cooled ion laser operating in this region of the spectrum has a typical electrical efficiency of only 0.001%).
Recent advances in intracavity-doubled miniature DPSS lasers, utilizing KTP as a doubler, have led to 0.1 W green output power. |