Realization of Cascaded Frequency Conversions Using a Single GdxY1-xCOB Crystal

In the field of nonlinear optics, cascaded frequency conversion is an effective method to obtain a solid-state laser source in the short wavelength region. By far, the most famous and popular frequency conversion approach is cascaded third-harmonic-generation (THG), which is composed of two steps: a phase-matching (PM) second-harmonic-generation, followed by a PM sum-frequency-generation. Correspondingly, two nonlinear optical (NLO) crystals are required. Theoretically, THG could be realized by utilizing only one crystal, as long as the frequency conversion processes occur at similar PM orientations and the polarization matching problem is solved. In this paper, we realized this approach by using one Gd
_x
Y
_1-x
COB crystal; an ultrawide angular acceptance was observed because the SHG process was noncritical phase matching, thereby providing the advantages of large angular acceptance and freedom from beam walk-off as the optimum PM approach in the NLO domain. Compared to the traditional cascaded THG configuration that requires two crystals, this configuration possesses the advantages of small volume, compactness, and low cost, all of which are favorable for practical applications.