Abstract
Characteristics of high-power, narrow-linewidth, continuous-wave (cw) green radiation obtained by simple single-pass second-harmonic-generation (SHG) of a cw ytterbium fiber laser at 1064 nm in the nonlinear crystals of PPKTP and MgO:sPPLT are studied and compared. Temperature tuning and SHG power scaling up to nearly 10 W for input fundamental power levels up to 30 W are performed. Various contributions to thermal effects in both crystals, limiting the SHG conversion efficiency, are studied. Optimal focusing conditions and thermal management schemes are investigated to maximize SHG performance in MgO:sPPLT. Stable green output power and high spatial beam quality with M(2)<1.33 and M(2)<1.34 is achieved in MgO:sPPLT and PPKTP, respectively.
Highlights
Compact, high-power, green lasers are of interest for a variety of scientific and technological applications such as material processing [1], human surgery [2], and laser display technology [3]
We have demonstrated a maximum SH green power of 9.6 W at a single-pass efficiency of 32.7% in MgO-doped periodically poled stoichiometric LiTaO3 (MgO):sPPLT and 6.2 W at a conversion efficiency of 20.8% in Periodically poled KTiOPO4 (PPKTP)
Power stability measurements performed in both crystals revealed a peak-topeak power fluctuation of 8.6% over 1 hour at fundamental power of 20 W in PPKTP, while in MgO:sPPLT a long-term power stability with a peak-to-peak fluctuation of 9% was recorded over 13 hours at a fundamental power of 29.5 W, confirming that stable and highpower generation with negligible power degradation is possible with MgO:sPPLT
Summary
High-power, green lasers are of interest for a variety of scientific and technological applications such as material processing [1], human surgery [2], and laser display technology [3]. With the rapid advances in fiber laser technology, access to high cw fundamental powers of tens of watts is no longer a limitation, making the choice of nonlinear material the most critical factor in the attainment of high optical powers and practical single-pass SHG efficiencies In this regard, the most important material properties include high optical nonlinearity, long interaction length, noncritical phase-matching capability, and high optical damage threshold to withstand the large cw optical intensities. The emergence of other QPM nonlinear materials such as MgO-doped periodically poled stoichiometric LiTaO3 (MgO:sPPLT) with improved optical and thermal properties [9], along with increased resistance to photorefractive damage and GRIIRA, has provided an attractive new alternative to further overcome the limitations due to thermal effects to permit cw green radiation at elevated power levels. Single-frequency performance and frequency stability characteristics of the generated green radiation are studied, and spatial beam quality measurements of the output are presented
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