All solid-state single-frequency DUV source at 248 nm

An all solid-state single-frequency 248 nm pulsed deep ultraviolet (DUV) source was realized based on multi-stage nonlinear frequency conversions of a 1064 nm fundamental driver. In detail, a 355 nm source, which is the third harmonic wave of 1064 nm laser, and an 827 nm source, which is the signal of an optical parametric oscillator (OPO) pumped by 532 nm laser, are combined for sum-frequency generation (SFG) to get the target wavelength of 248 nm. Finally, an average power of ∼120 mW was obtained at a 4 kHz repetition rate with a pulse width of 4.8 ns. The beam quality factor M² was measured to be less than 1.5, and the linewidth was estimated to be ∼250 MHz. This method is compact, robust, and requires only one single and easily accessible 1064 nm fundamental driver. The presented 248 nm source could serve as an excellent seed for the KrF excimer laser amplifier to improve the beam quality and coherence.