Nonlinear frequency conversion has been proven to be an attractive alternative to access spectral regions that are inaccessible to conventional laser sources. Still, the high-power, continuous-wave (cw) ultraviolet (UV) generation, based on frequency conversion processes, has been challenging due to the short-wavelength transparency cut-off and low nonlinearity of the available nonlinear materials. Some of the promising birefringent nonlinear materials for UV generation are LiB3O5 (LBO), β-BaB2O4 (BBO), and bismuth triborate, BiB3O6 (BIBO). The commercially available all-solid-state cw UV sources employ intracavity sum-frequency generation (SFG) schemes in LBO, which require mandatory active stabilization of the cavity and temperature phase-matching. On the other hand, single-pass schemes are simple, compact, robust, and do not require active stabilization. However, the low nonlinearity of LBO and BBO precludes them from single-pass SFG. The quasi-phase-matched (QPM) nonlinear material such as MgO:sPPLT with high nonlinearity and no spatial walk-off, also has transparency into the UV. However, 1st-order QPM SFG into the UV requires a grating period of ~2 μm, which is quite challenging to fabricate. As a result 3rd-order QPM, with a reduced effective nonlinear coefficient of 2.7 pm/V has been used to generate UV radiation under temperature phase-matching [1]. On the other hand, BIBO can be phase-matched at room temperature for UV generation by SFG of infrared and green, under type-I (ee→o) configuration [2]. It possesses high nonlinearity (deff~3.4 pm/V), bulk UV damage threshold (50 MW/cm2) and low UV absorption coefficient (αUV<0.02 cm−1).

© 2013 IEEE

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