<1.5cm-1 when pumped with a single frequency pump laser, and <4cm-1 when pumped with a broadband pump laser.
Photo acoustic spectra of NH3 at around 1600nm.
<1.5cm-1 when pumped with a single frequency pump laser, and <4cm-1 when pumped with a broadband pump laser.
Photo acoustic spectra of NH3 at around 1600nm.
<1mrad with any pump laser, resulting in record high doubling frequency.
2. The disadvantages of a type II BBO OPOs is
high in the short wavelength range (409-550nm), while low (about 1/2) in the over 640nm -710nm range, thus they require long crystals to work properly (>20mm). Longer crystal will result in larger walk-off and decrease efficiency, unless two counter rotating crystals are used.
Pumped at 355nm, to cover from 410nm to 710nm in the signal, type I BBO tunes only ~9° (crystal internal angle), while type II BO tunes about 21° . This much larger tuning angle also means that to cover the complete tuning range, the crystal has to has a much wider aperture in order to cover the complete tuning range.
In order to cover the complete tuning range efficiently, one has to use much longer and much wider crystals.
If one (Continuum Panther OPO) uses one single piece of BBO crystal of length ~20mm (the largest available), one has to consider the large walk-off effects in BBO crsytals. U-Oplaz Technologies' (UT) BBO-3B II OPO uses dual BBO crystals in a single cavity ("Simple, high-performance type II b-BaB2O4 optical parametric oscillator", Applied Optics, 36 (1997), 5898-5901). This dual-crystals design not only cancels the walk-off, but also the optical displacement --- giving non-movable beam positioning during wide tuning range. Single piece crystal costs less to tune because it only requires a single computer controlled digital acuator (saves costs on hardware ~$3,000), but is also much more expensive than 2 smaller crystals of the same length. To replace the BBO crystal, the single piece setup (Panther) costs at least $7,500, while the dual crystal design (U-Oplaz) only costs $4,500 total even when the 2 crystals' length is 4mm longer than the single crystal. Therefore, the UT design transfers the savings to the customer, although it costs about the same to make the type II OPO. The longer crystal length of the dual crystal design also adds about 1/3 to 1/2 more efficiency to the BBO-3B II OPO than the single crystal design.
UT's BBO-3B II OPO is offered as fully computer controlled, with Windows software.
It could be controlled by another computer through RS 232 port. To support the wide tuning range, one also has to first calibrate the OPO, and therefore a Wavelength meter with an accuracy of 1cm-1 or better from 400nm to 700nm is required. UT also offers the low cost X-Wave wavelength meter for easy calibration.
UT's type II OPOs are offered to be pumped at 355nm, 532nm and 1064nm. They could be pumped by any Nd:YAG laser with a smooth beam shape (with diffraction rings minimized), for example, the Indi, Lab and Pro series from Spectra-Physics, the SureLite, PowerLite and MiniLite series from Continuum and the Infinity from Coherent.
3. Doubler/Mixer
High power UV laser sources are important for a variety of industrial and scientific applications. For scientific experiment, we also desire wide tunability along with high power output. Researchers at UT have done extensive research into the high power scaling of UV harmonic generation, and have designed our products based on such research (Sheng Wu, et.al. Optics Communications, Vol. 173, 371-376, 2000, Paper 2928 and 2929 at Photonics West 2000).
The small divergence of the type II BBO OPO means high efficiency doubling or mixing into the UV. When pumped with a single frequency pump laser, the SHG efficiency is as high as 40%, and about 15% when pumped with a broadband pump laser. Scientists at NASA Langley Research laboratory generated 160mJ at 320nm for DIAL study, by mixing a type II OPO with the third harmonic of the Nd:YAG laser --- an efficiency of almost 75% (from the signal of the OPO to 320nm, see Photonics Spectra October, 1999).
Performance of a BBO-3B II OPO pumped at 355nm and doubled into the UV. The insert is the Photo Acoustic spectra of NO takend at 226nm.
To further extend into the UV efficiently, UT offers BBO-UV Doubler/Mixer system. Based on UT's detailed research on the thermal effects of borate crystals in the deep UV. UT designed the doubler/mixers that could generate high efficiency under high average power in the deep UV.
For example, a doubler/mixer was built for a high power dye laser (gives out >200mJ/pulse at 590nm) for combustion study at Caltech's Department of Aeronauotics. This doubler/mixer could generate about 80mJ at 287nm (for OH radicals), and about 22mJ at 226nm (for NO molecules), and the repetition rate is 10Hz. Another group at Caltech's Department of Geological and Planetary Sciences use the doubled OPO radiation to conduct photolysis experiment of N2O, where they have confirmed that photolysis in the upper atmosphere represents a significant sink of N2O (Science, 278, 5 Dec 1997, pp. 1778 - 1780 ). Here, over 300mW of 210nm is generated at 100Hz with a BBO-3B II OPO pumped by an Infinity 40-100 Nd:YAG laser from Coherent.
Again, the doubler and mixer from UT are also controlled by the same computer Windows software for OPOs. Users could easily intergrate UT's OPO or doubler/mixer system into their existing experiment.