A diffuser includes a front-side gradient surface formed from a diffuser block, a back-side gradient surface formed from the diffuser block, and opening structures formed from the front-side gradient surface to the back-side gradient surface. Each opening structure includes a conical opening having a first end along the front-side gradient surface and a second end corresponding to an apex at a depth within the diffuser block, and a cylindrical opening formed from the depth to the back-side gradient surface. The opening structures are arranged in rows including a first set of rows and a second set of rows alternately positioned along a length of the diffuser block.