Tsunami - Beckman Institute Laser Resource Center

Laser Description
2.4 -
2.2 -
2.0 -
1.8 -
g 1.6-
- 1.4-
z
g 1.2-
a 1.0-
0.8 -
0.6 -
0.4 -
0.2 -
700 750 800 850 900 950 1000 1050 1100
Wavelength (nm)
Figure 3-6: Tsunami Picosecond Tuning Curves
Wavelength Selection
The method used for wavelength tuning depends on whether the laser is
configured for fs or ps operation (Figure 3-3 and Figure 3-4).
fs systems. The fs Tsunami laser is wavelength tuned using a prism
sequence and a slit. This sequence provides a region in the cavity where
the wavelengths are spatially spread. A variable slit is located in this
dispersed beam. The output wavelength is tuned by changing the position
of the slit in the vertical plane. The width of the slit can also be changed
so that the bandwidth (and, hence, the temporal width) of the output pulse
can be varied. This simple, straight-forward method covers the entire
Ti:sapphire range for ultrashort pulses.
ps systems. The ps Tsunami laser is wavelength tuned using a birefringent
filter (bi-fi). The bi-fi consists of crystalline quartz plates placed within
the laser cavity at Brewster's angle. These plates are cut parallel to their
optical axes, and their birefringence causes the linear polarization of the incident
laser beam to become elliptical. A narrow range of wavelengths
makes a complete 180" (or multiple thereof) polarization flip and remains
linearly polarized; all other wavelengths remain elliptically polarized and
suffer losses at each Brewster-angle surface within the cavity and, thus,
fail to reach lasing threshold. The fiee spectral range of the bi-fi is the difference
between adjacent eigenwavelengths-those wavelengths that remain
linearly polarized after traversing the filter. Rotating the filter about
an axis normal to the plates changes these eigenwavelengths and, thus,
allows the output wavelength to be tuned.