Fig. 1. (a) Schematic of the liquid-cooled split-slab amplifier cell. The pink vertical line represents the laser beam. (b) Photo of the assembled amplifier.

Fig. 2. (a) Experimental setup used to characterize the amplifier in a four-pass configuration. The gain is measured using photo-diodes (PDs). Spatial distribution of gain is measured on a CCD camera. Wavefront distortion is measured with an HASO wavefront analyzer. (b) Single-pass gain distribution of the clear aperture of 90 mm × 90 mm (1 shot/min, 29 L/min). A gain average of 1.151 is obtained with a standard deviation of 0.013 over the 90 mm × 90 mm area.

Fig. 3. Spatial distribution of the amplified transmitted wavefront along a 1 h sequence at 1 shot per minute, flow rate of 29 L/min, as measured with the wavefront analyzer. A great stability of the wavefront is obtained with an RMS of less than 0.08% for the PV value over the whole sequence (see Table 1). Some vertical lines can be observed on some shots (e.g., shot #43), induced by the coolant flow.

Fig. 4. One-dimensional PSD over the (1–10 mm) range calculated from the wavefront measurements. Each envelope represents the minimum-to-maximum PSD variation along a 1 h sequence at a flow rate of 29 L/min for repetition rates of 1 shot/min, 1 shot/2 min and 1 shot/5 min, respectively. The purple dashed line is a guide to the eye representing a typical PSD specification for ICF laser slabs^[17,18].