Fabrication of Cryogenic Manganite Bolometers to Measure the Total Energy at the LCLS Free Electron X-Ray Laser

We are developing cryogenic bolometers to measure the total energy of the Linac Coherent Light Source (LCLS) free electron X-ray laser that is currently being built at the Stanford Linear Accelerator Center. LCLS will produce ultrashort ~ 200 fs X-ray laser pulses with ~ 10¹³ photons at 0.8 keV up to ~ 10¹² photons at 8 keV per pulse at a repeat interval as short as 8 ms, and will be accompanied by a halo of spontaneous undulator radiation. Our bolometer consists of a 375 mu m thick Si absorber and a Nd_0.67 Sr_0.33 MnO₃ sensor operated at its metal-insulator transition. It will measure the total energy of each pulse with a precision of < 1%, and is designed to meet the conflicting requirements of radiation hardness, sensitivity, linearity over a dynamic range of three orders of magnitude, and readout speed compatible with the LCLS pulse rate. Here we discuss bolometer design and fabrication, and the photoresponse of prototype devices to pulsed optical lasers.