Fig. 1. LG spectra of input signal and amplified signal pumped by Gaussian and flattop beams. (a) and (b) show the cases of w_p = w_s, 2w_s, and 3w_s for IG^e_4,0 and IG^o_4,2 signals at gain of 2, respectively. (c) LG spectra with different gain factors at w_p = 3w_s.

Fig. 2. Diagram of the OPA experimental setup, where the key components include the mirror (M), lenses (L1-L7), polarizing beam splitter (PBS), half-wave plate (HWP), spatial light modulator (SLM), spatial filter (SF), beam profiler (CMOS), and dichroic mirror (DM).

Fig. 3. Simulated and experimentally observed results of the OPA pumped by a Gaussian beam, where (a) shows the IG signal profiles; (b) and (c) are corresponding amplified signal profiles with w_p = w_s, 2w_s, respectively.

Fig. 4. Results of the OPA pumped by a flattop beam, where (a)–(c) show the theoretical beam profiles, the measured signals, and the corresponding amplified signals, respectively; (d) comparison of the far-field amplified light and the input signal obtained via experimental observation.

Fig. 5. Measured amplified signal energy and gain factor versus the input signal energy for IG-mode OPA. Inset, the overlap of the pump, IG^e_4,0, and IG^o_4,2 signals.