RbTiOPO4(RTP) crystal is a kind of nonlinear optical crystal material with excellent comprehensive properties. RTP is currently the most commonly used type of practical electro-optic crystals with high frequency repetition, high power and narrow pulse width laser Q switching. RTP electro-optical devices are not only used in laser micromachining and laser ranging, but also in major scientific exploration projects because of their excellent comprehensive performance.
RbTiOPO4(RTP)—a crystal with large nonlinear optical coefficient, large electro-optical coefficient, high photoresist damage threshold and stable physical and chemical properties
The growth temperature ranges from 950 °C to 800 °C and the growth period is usually between 45 and 60 days.As RTP is transparent from 0.4 to 3.5 μm, it can be used in multiple types of laser such as Er:YAG laser at 2.94 μm with fairly good efficiency. Bulk absorption measurements at 1.064 μm range from 50 to 150 ppm using Photothermal Common Path Interferometer.
Parameter
| High damage threshold | >15 J/cm2 at 10 Hz,10 ns at 1064 nm performed on coated crystals of 10 mm long |
| Low operating voltage | 1300 V for Y-cut and 1600 V for X-cut at 1064 nm applied to a crystal pair of 4×4 mm² for the aperture and 2×10 mm for the length |
| Low bulk absorption | <250 ppm/cm at 1064 nm |
| Average refractive index | 1.8 | ||||||
| Coeffcients in Sellmeier’s equation for 0.5<λ<3.5 μm | Ai | Bi | Ci | Di | Ei | pi | qi |
| 2.1982 | 0.8995 | 0.2152 | 1.5433 | 11.585 | 1.9727 | 1.9505 | |
| 2.2804 | 0.8459 | 0.2296 | 1.1009 | 9.66 | 1.9696 | 1.9369 | |
| 2.3412 | 1.0609 | 0.2646 | 0.9714 | 8.149 | 2.0585 | 2.0038 | |
| Transparency range, μm | 0.35 → 4.5 | ||||||
| Residual absorption (PCI) at 1064 nm | <250 ppm/cm | ||||||
| Electro-optical constants (@ 633 nm, 1 kHz), pm. V-1 | r13 | 10.9 | |||||
| r23 | 15 | ||||||
| r33 | 33 | ||||||
| Dielectric constant | εeff=13 |
| Chemical formula | RbTiOPO4 |
| Crystal structure | Orthorhombic |
| Point group | mm2 |
| Lattice parameters, Å | a 12.96 |
| b 10.56 | |
| c 6.49 | |
| Density, g.cm-3 | 3.6 |
| Resistivity (20°C, 20% Humidity), Ohm.cm | 1012 |
| Aperture, mm2 | from 2×2 to 9×9 |
| Length, mm | up to 10 |
| Dimension tolerance | ±0.1 mm |
| Flatness | <l/8 @633 nm |
| Surface quality | Scratch/Dig 10/5 |
| Parallelism | better than 30 arc sec |
| Perpendicularity | better than 30 arc min |
| Angle tolerance | △q < 0.5°, △f < 0.5° |
| Coating | AR coatings |
| Clear aperture | >90% central area |
| Transmitting wavefront distortion | less than l/8 @ 633 nm Dimension |
| Melting Point | ~ 1000 °C |
| Ferroeletric transition temperature | ~810 °C |
| Mohs Hardness | ~5 |
| Thermal Expansion Coefficients, /°C | a1=1.01×10-5, a2=1.37×10-5, a3=-4.17×10-6 |
| Hygroscopic Susceptibility | No |
| Ionic conductivity (room temperature, 10 kHz) | 10-8 S/cm |
- wide transparency range
- Stable mechanical and chemical properties
- High damage threshold
- Small volume
- Not easy to deliquesce
- High temperature stability
- Low half-wave voltage
- Suitable for high-frequency operation
Application：electro-optic modulator
High repetition rate (≥100 kHz) operation can be achieved by Q-switching, especially actively Q-switching, due to its stable pulse energy and low temporal jitter at high repetition rates. Active Q-switching mainly contains two commonly used Q-switch modes, acousto-optic (AO) Q-switch and electro-optic (EO) Q-switch. The AO Q-switched laser has the feature of high repetition rate (normally can reach 200 kHz), but it is limited in many fields due to its tendency to produce long pulse (typically several tens to one hundred nano-seconds). Compared to AO Q-switch, EO Q-switch can overcome the shortcomings of AO Q-switch, and get stable short pulses due to its fast loss change. But the EO Q-switch requires very high voltage driver; this leads the high pulse repetition rate is difficult to obtain. In recent years, with the development of new types of electro-optic crystals RTP, the repetition rates of EO Q-switched solid state lasers have been improved significantly.
Application：electro-optic Q-switchhttps://www.laser-crylink.com/wp-content/uploads/2019/07/17-High-repetition-rate-880-nm-diode-directly-pumped-electro-optic-Q-switched-Nd：GdVO4-laser-with-a-double-crystal-RTP-electro-optic-modulator.pdf
A high pulse repetition frequency Nd:YAG twisted-mode laser uses an RTP crystal as the electro-optic Q-switch. Stable single-longitudinal-mode laser beams at 1, 5, and 10 kHz were obtained with a linewidth less than 0.1 GHz. Under an incident pump power of 7.5 W and a PRF of 10 kHz, the maximum output power of the single-longitudinal-mode laser was 1.19 W. The corresponding conversion efficiency, single pulse energy and pulse peak power were 15.8%, 119 μJ, and 2.5 kW, respectively.
RTP Q-switched single-longitudinal-mode Nd:YAG laser with a twisted-mode cavity
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