Fig. 1. (a) Dependence of the central diffraction efficiency of the VBG on the product of the refractive index modulation and grating thickness; (b) angular selectivity of the VBG and HVBG.

Fig. 2. Principle of the BSF based on HVBGs.

Fig. 3. Diagram of band-stop filtering in a two-stage amplifier system.

Fig. 4. Angular selectivity of the HVBGs used in the simulation.

Fig. 5. Near-field beam profiles of (a) the incident beam, (b) output beam from Amp.1, and output beams from the two-stage amplifier system (c) without BSF and (d) with BSF.

Fig. 6. The dependence of near-field modulation on the accumulated B integral.

Fig. 7. Dependence of the normalized PSD on the spatial frequency both in (a) the $x$ direction and (b) the $y$ direction for the incident beam, the output beam from Amp.1 and the output beams from the two-stage amplifier system without and with two-dimensional BSF.