You won’t be able to use KTP for outputting short wavelengths. If we could, 473nm would be more efficient and cheaper to obtain. LBO, BBO and BiBO are typically used for producing <500nm. BiBO has the best efficiency but it is expensive and hard to get hold of. LBO is by far the most common crystal to use other than KTP. Crystals require phase matching, so you need to know the angle of which to orient the crystal to produce doubled output. Some crystals are cut with the phase matching angle already considered, so they are easy to use. Bare in mind that with directly doubled diodes the output beam will be dependent on the input beam specs. So poor beam quality in will have poor beam quality out.