Alignment and focusing device for a multibeam laser system Page: 2 of 5
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ALIGNMENT AND FOCUSING DEVICE FOR A MULTIBEAM LASER SYSTEM*
William C. Sweatt
University of California, Los Alamos Scientific Laboratory
Los Aimos, NM 87545
Abstract
Large inertial confinement fusion laser systems have many beams focusing on a small target. The Antares
system is a 24-beam C02 pulse laser. To produce unIform illumination, the 24 beams must be individually
focused on (or near) the target's surface in a symmetric pattern.
To assess the quality of a given beam, we will locate a Smartt (point diffraction) interferometer at the
desired focal noint and illuminate it with an alignment laser. The resulting fringe pattern shows defocus,
lateral misalignment, and beam aberrations; all of which can be minimized by tilting and translating the fo-
cusing mirror and the preceding flat mirror.
The device described in this paper will remotely translate the Smirtt interferometer to any position in
the target space and point it in any direction using a two-axis gimbal. The fringes produced by the inter-
ferometer .e relayed out of the target vacuum shell to a vidicon by a train of prisms. We are designing
four separate "snap-In" heads to mount on the gimbal; two of which are Smartt interferometers (for 10.6 um
and 633 nm) and two for pinholes, should we wish to put an alignment beam backwards through the system.
Introduct on
A device is described that will aid in the alignment of the Antares laser system.1 Antares is a
pulsed C0 laser, which is being built to study inertial confinement fusion. It has 24 beam lines, which
deliver 4-k.l total energy. These 24 Deams must be focused on the target with a minimum amount of aberra-
tion. This ,, the purpose of the device explained here. it consists of a Smartt point diffraction inter-
rerometer2 that can be inserted into the target volume on the target insertion track. The Smartt inter-
ferometer is centered on a 2-axis gimbal so it can be pointed at any ona of the 24 beams. The gimbai is
mounted on a 3-axis translation stage ( ' mm travel) so it can be moved to any point in the target volume.
The system has been designed so that ei. or a 633-nm or a 10.6-um Smartt interferometer can be used. This
allows a tremendous range in sensitivity. Figure la is a schematic of the system.
As an alignment sequence, the Smartt is inserted into the target-vacuum shell and located where 1 of the
94 beans is supposed to focus. It is then pointed at the beam to be adjusted. The interference fringes seen
wuen it is illuminated with an alignment laser show defocus, tilt, and aberrations. The focus can be ad-
justed by translating the focusing parabola. The tilt can be corrected and the aberrations minimized by an
appropriate combination of tips and tilts of the parabola and the preceding flat mirror,
Using the Smartt interferometer will be a lengthy process (estimated 4 hours); so the pointing of the
first few beams could change slightly before the last ones are finished. Fortunately, minor pointing cor-
rect'Ions have an insignificant effect on the aberrations, hence a scheme that luickly currects small point-
ing errors alone could be quite useful. The following scheme is one possibility.
This gimbal system can also he used in the reverse direct lun. The vidicon can he replaced with a laser
and the alignment laser can be replaced with an alignment telescope. The Smartt interferometer would be re--
placed with a pinhole. The resLlt is c point source of light thiL can be located at any point In the target
volume where a bcrm should focus (Fig. lb). The pointing error will be seen by the alignment telescope so
it can be zeroed.
'n this paper , the optical and mechanical design of the system will be discussed. The gimbal is pres-
ently being fabricated. The prototype should be under test early in 1981.
DrsIign
The device mut be moderately small, so it can fit through the target insertion air lock. This makes
it difficult to install a vidicon on the gimbal. Also, cooling a vidiron in an evacuated region would be
hard, Iherefor', the vidicon has been located outside the vacuum shell, and the image of the Smartt inter-
fernmeter is relayed out by a system of mirrors and prisms. If the image is transferred nut through the
gimb. I aues, the image rotates bot does not translate. Ti's prisms shown in flg. 2 accomplish this. (The
usagt' is rotated usaig the "K" pri im s'own in Fig. Ia.) he prisms are beirg made out of 'ti'c selon ide
(/nSe), on" of the few materials that will .c nsmin it both 633 nm and 10.6-um radiation. The advantages ofIgInVi p : , in der the dm1pico, of th^ 1. S. Department of Fnergy
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Sweatt, W.C. Alignment and focusing device for a multibeam laser system, article, January 1, 1980; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1055580/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.