Fig. 1. Attenuation of laser intensity using a random pinhole attenuator (RPA). (a) Schematic diagram for attenuating the laser intensity using the RPA. (b) Intensity of the laser beam on the yz-plane shown in (a). (c) Intensity distribution at the focal plane calculated for different numbers of pinholes.

Fig. 2. Random pinhole array fabricated with a number-density gradient. (a) Simplified model of the random pinhole array. (b), (c) Microscope images of the random pinhole array obtained with (b) 20× and (c) 50× magnification.

Fig. 3. Beam profiles of the focused beam. (a)–(d) The beam profiles of the focused beam and the distorted beam. The intensity is attenuated using (a), (c) an ND filter (Thorlabs NDC-100C-4M) and (b), (d) a random pinhole attenuator (RPA). (e) The intensity lineouts along the x-axis of the beam shown in (a) and (b). The x-axis represents the distance from the beam’s center, while the y-axis depicts the relative intensity on a logarithmic scale. (f) The measured optical density versus the angle of the variable attenuation board. OD denotes the optical density.

Fig. 4. Photos of an RPA. (a) RPA fabricated on an aluminum foil by laser drilling. (b) Magnified image showing randomly distributed pinholes. (c) Image of a pinhole.

Fig. 5. Beam profiles of the CoReLS 4 PW laser. (a) Beam profile of the focused 10-μJ laser beam without passing through the plasma mirror system and (b) beam profile of the focused laser beam obtained with the plasma mirror system. The energy of the laser beam was 80 J before the grating pulse compressor. (c) The schematics of the CoReLS 4 PW laser. The plasma mirrors (PMs), RPA and off-axis parabola (OAP) are shown.

Fig. 6. Comparison of temporal characteristics of two attenuation cases. (a) Laser electric fields obtained with an ND filter (red line) and with an RPA (blue line). (b) Spectral intensities and phases of the two cases.