Abstract
A 2 W deep-ultraviolet (DUV) source at 274 nm with 5.6 kW peak power is demonstrated by frequency quadrupling a diode-seeded, polarization-maintaining (PM), Yb-doped fiber master oscillator power amplifier (MOPA) system delivering 1.8 ns pulses at a repetition rate of 200 kHz. The second harmonic generation (SHG) and the fourth harmonic generation (FHG) are achieved by using Lithium Triborate (LBO) crystal and β-BaB2O4 (BBO) crystal in sequence, with an IR-to-green and green-to-UV conversion efficiency of up to 65% and 26%, respectively. This is the first kW peak power pulsed UV system reported at 274 nm which has great potential for machining insulators, 2D materials, isotopic separation of Calcium-48, and fluorescence analysis of biological molecules.
Highlights
Ultraviolet (UV) lasers are attractive solutions for many applications, such as machining [1], fluorescence research [2], and photolithography [3], because of their higher photon energy, smaller focus spots and larger absorption cross section in most materials in comparison to visible and infrared (IR) sources
High-brightness UV light is frequently obtained by nonlinear frequency conversion of Ti:Sapphire lasers with wavelength near λ~800 nm [6], and Nd-doped solid-state lasers [7] or Yb-doped fiber lasers [8] around λ~1 μm
The Yb-doped fiber amplifier (YDFA) exhibits a relatively broad gain band in the near-IR wavelength range around λ~1-1.15 μm [9]
Summary
Ultraviolet (UV) lasers are attractive solutions for many applications, such as machining [1], fluorescence research [2], and photolithography [3], because of their higher photon energy, smaller focus spots and larger absorption cross section in most materials in comparison to visible and infrared (IR) sources. MOPA systems can take full advantage of both the diode laser seed, which provides flexible wavelength tuning and serves as a frequency selector, and the fiber amplifier, which allows for the high brightness amplification over a wide wavelength range. It enables similar advantages in the visible and ultraviolet when frequency conversion techniques are used. The difficulty originates from the fact that λ~1.1 μm emission is close to the edge of the Yb gain band This necessitates a long active fiber to push the gain peak towards the longer wavelength edge and as such the maximum peak power extraction is primarily limited by the nonlinear effects within the long device length. The SHG and the FHG were achieved by using LBO crystal and BBO crystals in sequence, providing an IR-to-green and green-to-UV conversion efficiency as high as 65% and 26%, respectively
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