Third Harmonic Generation

The Sirah THU-205 (third harmonic unit) is designed to generate laser radiation in the UV wavelength range, from 197 to 260 nm, by third harmonic generation (THG). It is operated together with a Nd:YAG pumped dye laser, either a PrecisionScan or a Cobra-Stretch model.


The dye laser is operated in the red spectral range, from 591 to 780 nm. Its output beam is first frequency doubled by a temperature stabilized BBO crystal. Then, the resulting UV beam is sum frequency mixed with the residual dye laser beam in a second temperature stabilized BBO crystal. A set of 4 dichroic mirrors separates the generated UV beam from the two incoming. Due to the short wavelength, different dichroics sets are necessary to cover the wavelength range of the THU-205. Alternativly a wavelength separation with four
Pellin-Broca prisms made of very high quality CaF2 can be used. This unit is mounted vertically behind the THU-205 (+ 171 mm in length). It can be mounted also horizontally behind the doubling unit for separation of the second harmonic generation (SHG).

Optical Layout


Tuning Range

WS-THU 4x Pellin-Broca prisms 190 – 450 nm
With DC-195 dichroics set 190 – 200 nm
With DC-205 dichroics set 200 – 210 nm
With DC-215 dichroics set 210 – 220 nm

Tuning curves for 500 mJ @ 532 nm pump laser energy.

General Characteristics

1) single crystal operation, requires WS-Auto Pellin-Broca unit
Energy Output 1% of pump laser energy
Linewidth approximately √3x dye laser linewidth / cm-1
Wavelength range with THG 197 – 220 nm
220 – 260 nm (SHG-215-T + SHG-280-T, optional)
Wavelength range with SHG 1) 206 – 220 nm (THG-197-T crystal, included)
215 – 280 nm (SHG-215-T crystal, optional)
250 – 380 nm (SHG-250-T crystal, included)
Maximum Pump Energy 650 mJ, with standard dye cell
800 mJ, with enhanced beam profile cell
1400 mJ, with 2nd main amplifier
Dye Laser Resonator 2400 lines / mm grating recommended
1800 lines / mm grating possible
Repetition Rate 10 Hz recommended
Crystal Tuning Mode look-up table (Autotracking optional)
UV Beam Polarization vertical, > 98 %
UV Beam Diameter (typical) 3 – 6 mm, depending on amplifier cell type
UV Beam Divergence < 0.5 mrad



All Dimensions in mm. Specifications are subject to change without notice.

Literature & Downloads

Datasheet THG