Free electron laser device for scanning a spatial field

A free electron laser device for conically scanning a spatial field, said device comprising:

• a drift tube disposed concentrically about the longitudinal axis of the device,
• mandrel means of less diameter than the drift tube being concentrically and rotatably mounted therein so as to define an annular space between the mandrel means and the drift tube interior surface,
• cooperating power supply means and magnetic field means for generating and guiding a free electron beam of annular shape as it propagates in a direction longitudinally of the tube toward its outer end and in the annular space between the tube and mandrel means,
• Wiggler magnetic field means concentrically disposed about the drift tube for generating a magnetic field in a direction generally transverse of the device longitudinal axis, the Wiggler magnetic field means for exciting the electrons of the beam to lase and form a radiation wave front of annular shape in the annular space between the tube and mandrel means, the wave front propagating toward the tube outer end.
• a series of canted mirror means of washer-like configuration disposed about the mandrel means, each of the mirror means extending generally transverse of the mandrel means and being pivotally connected to the mandrel means for limited movement about a pivotal axis generally transverse of the longitudinal axis of the device, each mirror means being longitudinally spaced a predetermined distance from an adjoining mirror means and having an inside diameter greater than the diameter of the mandrel means while at the same time having a outside diameter less than the inside diameter of the drift tube,
• actuator means mounted on the mandrel means and connected to each mirror means of the series for selectively controlling the pivotal movement of each mirror means, and
• motor means connected to the mandrel means for rotating the same about its longitudinal axis including the series of canted mirror means during formation of a propagating annular wave front in the annular space so that each of the canted mirror means reflects various waves of the front in order not only to redistribute the reflected waves to form asymmetrict diffraction patterns in the annular space but also to progressively steer the patterns toward the device outer end so as to form an asymmetric diffraction patterned laser beam and to project the laser beam from the device outer end into a spatial field about the device longitudinal axis and at an angle thereto such that the major lobe of the projected beam conically scans a region of the field about the device axis during rotation of said mandrel means.

A method for conically scanning a spatial field, said method comprising the steps of:

• generating a free electron beam of annular configuration for propagation within and along the annular space between a drift tube and rotatable mandrel means and in a direction toward the tube outer end, the mandrel means being concentrically disposed in the tube and arranged in alignment with the device longitudinal axis.
• subjecting the electrons of the beam to a Wiggler magnetic field disposed transversely of the device longitudinal axis so as to excite the electrons to form a wave front of annular shape that propagates in a direction toward the tube outer end,
• reflecting various waves of the wave front by a series of canted mirror means disposed about the mandrel means in longitudinally spaced relation to each other, each mirror means also being arranged at a predetermined angle in relation to a plane transverse of the mandrel means, the mirror means not only redistributing the phase of the reflected waves so as to form asymmetric diffraction patterns in the annular space but also to progressively steer the diffraction patterns of the reflected waves towards the outer end of the device so as to form an asymmetric diffraction patterned laser beam all during rotation of the mandrel means, and
• continuously projecting the laser beam of conical shape from the outer end of the device into a spatial field, a radial cross-section of the projected beam having a major lobe disposed at an angle about the device axis such that the major lobe conically scans the field during rotation of the mandrel means.