Synchronous pumped femto-second optic parametric oscillator based on PPLN
With the advent of Optical Parametric Oscillator (OPO), new lasers with tunable wavelength appear. The laser can work at various wavelengths easily based on OPO. Moreover, OPO has so many advantages, for example: high contrast ratio, widely tunable wavelength range, various tuning methods, etc, which compare to traditional oscillators.
Nanosecond and picosecond OPO’s are well developed up to now. There are so many commercial products. But femtoseond OPO is still in studies due to much more difficult to synchronization to the pump laser, as well, high energy femtosecond pump laser is difficult to get. As for the applications, for example, femto-chemistry, femto-biology, ultrafast resolution and wavelength resolution experiments need femtoseond pulse at different wavelength.
We build a OPO, which pumped by a home-made Ti: sapphire oscillator. The configuration of OPO is shown in Figure 1, which based on PPLN nonlinear crystal( periodic poled LiON3 ). The pumping laser from Ti: sapphire oscillator works with 900mW in 46fs, and the central wavelength is 800nm with bandwidth of 23nm, which are shown in figure 1.
Figure 1. (a) the central wavelength of the T:S oscillator is 800nm,spectral width is 23nm;(b) the pulse duration is 46fs.
The pumping Laser is focused into the PPLN by a lens with focus length of 100 mm. The OPO cavity is very similar to the Ti: s cavity, in which two concave mirrors with radius of 100 mm are used as accumulating the fluorescence, a 5% transmission mirror as output coupler and 4 high reflectivity at 1.1~1.3 mm mirrors are used. The schematic of the OPO is shown in Figure 2.
Figure 2 Configuration of OPO
By tuning the length of cavity, or pump wavelength, and temperature of nonlinear crystal, the OPO can work fine, which wavelength tunable from 1.1 to 1.3um. The corresponding idler central wavelength is 2.93~2.08um. The tunable wavelength range of signal is shown in Figure 3.
Figure 3 tunable wavelength range of signal
The pulse duration is 167fs, measured by a autocorrelator, which is shown in Figure 4.
Figure 4 pulse duration is 167fs at 1225 mm
In near future, we will build OPO in UV range. By combining OPO and synchronization technology, we will build a frequency comb system which can cover spectrum range from UV to IR.
Now we are building a new OPO which works at 1053nm, which will be the seed for high energy Nd glass amplifier, due to its high contrast ratio and high beam quality. But the power stability and central wavelength stability must be very high for this seed, so corresponding feed back loops are in studies for control power and central wavelength.