Measured Beam Deformations in a Guide Made of Tubular Gas Lenses

Tubular gas lenses have possible use as focusing elements in an optical beam waveguide. 1,2 Theoretical analysis has shown that thermal gas lenses are not ideal; beam distortion from the cumulative effect of lens aberrations 2 " 6 and the beam wandering resulting from lens misalignments 7 - 8 limit the number of lenses that can be used in a beam waveguide. Beyond this number, corrective devices such as redirectors, refocusers, and mode filters must be used. 0 ' 10 Redirectors sense the position of the beam and introduce deflections which tend to realign the beam with the guide axis. Refocusers sense the increase of beamwidth and tend to focus the beam back to its ideal profile. Mode filters reduce the content of unwanted higher order modes. Previous experiments indicated difficulties with the accurate alignment of the lenses.11 From this experience we worked out a method of alignment by which we achieved satisfactory accuracy and beam stability. Subsequently we measured the deformation of the beam transmitted off axis and around a bend and compared it with theory. We compared beam distortions for nonconfocal lens spacings with those of confocal geometry. 179