Transmitted laser beam diagnostic at the Omega laser facility

We have developed and commissioned a transmitted beam diagnostic (TBD) for the 2ω high intensity interaction beam at the Omega laser facility. The TBD consists of a bare-surface reflector mounted near the target, which collects and reflects 4% of the transmitted light to a detector assembly outside the vacuum chamber. The detector includes a time integrating near-field camera that measures beam spray, deflection, and the absolute transmitted power. We present a detailed description of the instrument and the calibration method and include first measurements on laser heated gas bag targets to demonstrate the performance of the diagnostic