According to Sellmeier equation

the calculation and analysis on the collinear sum-frequence generation and frequency doubling in biaxial crystal LiB

3

O

5

(LBO) are made in terms of principle axes. The results demonstrate that sum-frequency mixing of a Nd:YAG laser

<

1.064nm)and a dry laser (from 0.56μm to 0.85μm) radiation can be realized in both of the two types of phase-matching(PM)process. Type Ⅱ PM is generally more efficient than that of type Ⅰ

while type Ⅰ is phase matchable over a larger wavelength range. As mentioned in the latter

0.266μm UV radiation can be generated by sum-frequency mixing of the Nd:YAG laser with 1.064μm radiation and its third-harmonic generation with 0.355μm radiation by type I PM process in LBO crystal.An interesting feature of sum-frequency generation and frequency doubling in LBO is that non-critical phase matching(NCPM)can be obtained in x-y plane (type Ⅰ PM)and in y-z plane (type Ⅱ PM) at room temperature

while the nonlinear coefficient deff reaches its maximum. NCPM ensures the advantage of both a large acceptance angle and a small walkoff angle

thus makes LBO with a longer coherent length and higher efficiency in frequency conversion. The curves of the phase matching angle

effective nonlinear coefficient

walkoff angle

acceptance angle and spectral bandwidth versus the fundamental wavelength are plotted according to the formulas we derived in type I PM in x-y plane and type Ⅱ PM in y-z plane

respectively. The theoretical guiding to experiments and applications in LBO is presented.