Phase matching retracing behavior for second harmonic generation in LiB3O5 crystal

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Abstract
The nonmonotonic relation between the increasing wavelength and the noncritical phasematching (NCPM) temperature are analyzed in detail for temperature‐tuned as well as the phase matching angle for angle‐tuned second harmonic generation in a LiB3O5 (LBO) crystal. This relation was called ‘‘the phase matching retracing behavior.’’ Because of the retrace, LBO is the unique nonlinear optical crystal that can produce the spectra through blue to near infrared by NCPM. It has been shown that the retracing wavelengths (∼1.3 μm), and furthermore, the conjugation relation for phase matched wavelengths are approximately independent of the tuning means. There exist at the retracing wavelengths not only the retrace for the tuning curves but also for the beam walkoff, group velocity mismatch, and the angular and spectral acceptances. The spectral noncritical phase matching is achieved and the group velocity mismatch is zero at the retracing points. The temperature acceptances are also very large. These properties of LBO, combining its high damage threshold, high transparency, nonhygroscopicity, and the availability of the large and high quality crystal, make LBO the best choice in doubling, either by type I or type II, by temperature‐tuned or angle‐tuned, the radiations (including ultrafast pulses) in the vicinity of 1.3 μm, such as those from some diode lasers, optical parametric oscillator/amplifier, and Nd:YAG/YAP/YLF lasers working at 4F3/2–4I13/2 transition.