Cailabs Canunda Axicon User manual

INSTALLATION MANUAL
IINSTALLATION MANUAL

©Atypix

Table of content
1. Safety ............................................................................................................................................. 4
2. Recommended equipment for installation ....................................................................................... 4
3. Handling ......................................................................................................................................... 4
4. Typical optical setup ....................................................................................................................... 5
5. Installation ..................................................................................................................................... 6
Preliminary ........................................................................................................................................................................... 6
Laser source collimation ................................................................................................................................................... 6
Telescope installation (optional) ...................................................................................................................................... 7
Pre-positioning of axicon................................................................................................................................................... 7
Pre-alignment mirrors ...................................................................................................................................................... 8
Axicon alignment ................................................................................................................................................................10

4
1. Safety
• Always use gloves when handling the axicon.
• Always handle the axicon by its sides.
Beware of the risks involved when working with your laser. Check your laser eye safety class and follow the recommendations.
Follow the guidelines provided by the manufacturer of your laser source.
2. Recommended equipment
for installation
• Gloves
• Screwdriver
• IR card
• Beam block
• Straightedge ruler
• Iris diaphragm (optional)
• Camera
• Optical rail
• ND ilters
3. Handling

5
4. Typical optical setup
A typical optical setup for the generation of Bessel beams
and/or ring-shaped beams includes a collimated laser source,
alignment mirrors and a relective axicon. A telescope (optional)
might be needed to accommodate the laser beam diameter.
The optical elements needed are:
• 1x Lens Lcfor collimation (with mount)
• Optional - 2x Lenses Lt1 and Lt2 for the telescope (with
mount)
• 2x Alignment mirrors (with kinematic mount)
• 1x Relective axicon (with 2” rotation mount)
• 1x Plane mirror suited for the 2” rotation mount (for
preliminary alignment)
Installing the reflective axicon in this setup
requires 5 steps:
1. Laser source collimation
2. Telescope installation (optional)
3. Axicon pre-positioning
4. Mirrors pre-alignment
5. Axicon alignment

6
5. Installation
• Make sure that you have all the necessary tools.
• Start by placing every optical element with their holders
on the optical bench, following the schematic described in
section 4.
• Put every component at the same general height using the
straight edge ruler
• Place the beam block where needed (It will be placed after
the optics currently being aligned to avoid any incident)
• Do not place the camera on the beam path right now
Most laser outputs are already collimated, this step is only required if your laser is not collimated. A collimated laser
beam has a constant diameter over its propagation.
Preliminary
Laser source collimation
• 1x Lens Lcwith an EFL ƒc
Note: If the divergence of the laser source θ is known, the EFL
ƒcof the collimating lens can be chosen in order to obtain the
beam diameter Φ needed for the axicon, as they are related
according to the formula below:
ƒc=Φ
(2 tanθ)
To collimate your laser source, place the lens Lcat a distance ƒc
from the output of the laser source:
To verify that the collimation was done correctly, scan the IR
card along the laser beam after Lc. Collimation has been done
correctly when the diameter of the spot on the IR card stays
constant and maintains its circular shape when you scan the IR
Card along the laser beam.
• If the spot diameter increases over the optical axis, in-
crease the spacing between the lens and source output. If
it decreases, decrease this spacing.
• If the spot is not circular (elliptical), this shows that the
laser beam not pass by the lens’center. Reposition the lens’
height, lateral position and tilt until the beam is circular.
Possible diiculties:
Procedure:
Equipment needed:

7
Telescope installation (optional)
The laser beam diameter may need to be adjusted to it the axicon with the recommended dimensions. To adapt the
collimated beam diameter, a telescope must be installed.
Equipment needed:
• 1x Lens Lt1 with an EFL ƒt1, with mounts
• 1x Lens Lt2 with an EFL ƒt2, with mounts
ƒt2
ƒt1
• If the diameter of the spot increases along the optical axis,
move the lens Lt2 a bit farther away from the lens Lt1. If it
decreases, move it closer.
• If the beam propagates upward, downward, or laterally, or
if the spot is not circular (elliptical), it means that the laser
beam does not pass by the lenses’ center. Reposition the
lenses’ height, lateral position and tilt until the beam path
is correctly adjusted and the beam is circular. To ensure
that the beam is passing by the lenses’ center, you can put
an iris in front of the telescope, only allowing the central
part of the beam to propagate.
Pre-positioning of axicon
To correctly position the axicon at the recommended of-set
angle α,put a plane mirror inside the axicon mount. Place the rail
at an angle of 2α(since relection doubles the incidence angle)
corresponding to the beam relected onto the mirror placed in
the axicon mount.
To verify that the telescope has been correctly installed, move
the IR card along the laser beam after Lt2 over at least 1m. The
diameter of the spot on the IR card should stay constant and
maintain its circular shape when you scan the IR Card along the
laser beam.
Possible diiculties:
Procedure:
To enlarge the collimated beam diameter by a factor of ,
place the lenses Lt1 and Lt2 at a distance d=ƒt1+ƒt2 from each
other:

8
The alignment mirrors allow you to adjust the laser beam optical axis with the requested input optical axis of the axicon.
Pre-alignment mirrors
Place the beam block in front of the axicon mount (currently
holding a mirror). Visually preposition the mirrors in the right
position. By moving the kinematic mounts and with the visual
help provided by the IR card, position the beam roughly at the
center of the axicon mount, where the axicon will be.
Align the irst mirror so that the beam exiting the second mirror
is at the correct lateral position and same height as the axicon
center. Then align the second mirror to ensure that the beam
remains horizontal and aims at the center of the axicon mount.
Equipment needed:
• 2x Alignment mirrors, with kinematic mounts
• 1x Relective axicon, with 2” rotation mount
Procedure:

9
Once broad alignment is completed, turn the source of and
move the beam block from being in front of the axicon mount to
behind the axicon.
Right now, there is still a mirror in the axicon mount. Adjust
the mount angle to have the relected beam propagating at the
angle deined by the rail (installed in 4.4).
Using the IR card, scan the beam path to verify that the beam
follows the rail. If not, adjust the mirror angle.
• Make sure that the beam is completely relected by
the mirrors and not cropped at the edges. This is easily
conirmed by ensuring the circularity of the beam (with an
IR card if using an IR laser) after each mirror. If the beam
is cropped, check the shape of the beam before and after
each optic. Once you have found out where the beam is
cropped, adjust the previous optics position or angle until it
is no longer cropped.
Possible diiculties:

10
Axicon alignment
When the mirror in the axicon mount is correctly positioned,
replace it with the axicon. The axicon’s substrate has a lat
edge that can be used to achieve the correct rotational position.
This lat edge should be placed at the top.
[
Axicon’s
lat edge
With the IR card, scan the beam path to see where the Bessel beam and the ring-shaped beam are generated:
Bessel beam in near ield (left), ring-shaped beam in far ield (right)
Here, the two mirrors alignment technique can be used where
the irst mirror is adjusted to ensure correct positioning in
near ield (i.e. that the beam exiting the second mirror is at the
same height as the axicon center and that the beam is at the
correct lateral spot just after this second mirror). The second
mirror is then adjusted to aim at the center of the axicon. By
doing so, the beam position right behind the second mirror is
modiied and needs to be adjusted through an iterative process,
alternating between alignment of the irst and second mirror.
From a visual perspective, you should see a circular beam behind
the axicon with a homogeneous intensity, except at the center
where it brightens (corresponding to the central spot of the
Bessel beam). This beam will propagate over tens of centimetres
(depending on the axicon and system in use) and slowly evolve
into a donut shape.
A irst alignment can be performed visually by observing if the
beam in near ield is circular and if its bright spot is centered. In
far ield, you must verify that the ring is circular.
By adjusting the two mirrors placed before the axicon, the user
ensures the injection angle and position are correct. The irst
mirror allows adjustment in near ield whilst the second one
allows correction in far ield.
As mentioned before, this will be an iterative process, going
back and forth between aligning the irst and second mirror.

11
Once this general alignment is obtained, place the camera on
the rail, and set it up (sensitivity, contrast…) to observe the
beam generated by the axicon. If necessary, place a ND ilter in
front of the camera.
You can then repeat the above process by moving the camera
from near to far ield by using the rail.
Possible diiculties:
• If the central lobe of the Bessel beam is split in several
spots, the axicon is not correctly rotated. Slightly change
the rotation of the axicon until the central lobes uniies.
• Once the mirrors have been ine-tuned, a proper
measurement of the depth of ield of the generated
Bessel beam can be performed. If the experimental depth
of ield greatly difers from the theoretical one while the
beam shape seems appropriate, this is a symptom of bad
collimation. The user can adjust collimation (by varying
the spacing inside the telescope for example). Check the
collimation by scanning the IR card along the laser beam
in front of the axicon. Collimation has been correctly done
when the diameter of the spot on the IR card remains
constant when you scan the IR Card along the laser beam.

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07/2019 – Cailabs reserves the right to modify the speciications without prior notice. Printed on PEFC™ certiied paper (Programme for Endorsement of Forest Certiication schemes).