Catherine S. Plesko (Los Alamos National Laboratory), R. Ryan Clement (Los Alamos National Laboratory), Robert P. Weaver (Los Alamos National Laboratory), Paul A. Bradley (Los Alamos National Laboratory), Walter F. Huebner (Southwest Research Institute)
Keywords: Astronomy
Abstract:
For the last two decades adaptive optics has been used as a technique for correcting imaging applications and directed energy/laser targeting and laser communications systems affected by atmospheric turbulence. Typically these systems are bulky and limited to <10 kHz due to large computing overhead and limited photon efficiencies. Moreover most use zonal wavefront sensors which cannot easily handle extreme scintillation or unexpected obscuration of a pre-set aperture. Here we present a compact, lightweight adaptive optics system with the potential to operate at speeds of MHz. The system utilizes a hologram to perform an all-optical wavefront analysis that removes the need for any computer. Finally, the sensing is made on a modal basis so it is largely insensitive to scintillation and obscuration. We have constructed a prototype device and will present experimental results from our research. The holographic adaptive optics system begins with the creation of a multiplexed hologram. This hologram is created by recording the maximum and minimum response functions of every actuator in the deformable mirror against a unique focused reference beam. When a wavefront of some arbitrary phase is incident on the processed hologram, a number of focal spots are created – one pair for each actuator in the DM. The absolute phase error at each particular actuator location is simply related to the ratio of the intensity of each pair of spots. In this way we can use an array of photodetectors to give a direct readout of phase error without the need for any calculations. The advantages of holographic adaptive optics are many. To begin with, the measurement of phase error is made all optically, so the wavefront sensor directly controls the actuators in the DM without any computers. Using fast, photon counting photodetectors allows for closed loop correction limited only by the speed of the deformable mirror which in the case of MEMS devices can be 100 kHz or more. All this can be achieved in an extremely compact and lightweight package making it perfectly suited to applications such as UAV surveillance imagery and free space optical communications systems. Lastly, since the correction is made on a modal basis instead of zonal, it is virtually insensitive to scintillation and obscuration. Date of Conference: September 1-4. 2009
Track: Astronomy