today with Manar, we brought the Koheras to the Minicav optical room and aligned it with the Iris used for the cavity.

but if I properly understood what Manar said to me, the cavity mirrors have been moved by roughly 1cm after Daniele and Manar finished the alignment.
with what we saw today, it seems the cavity is not aligned anymore.... we will check that tomorrow with Daniele.
we have a beam at the output window but I'm quite sure it only goes through M1 and not M2 anymore... and then directly to the output window in between M2 and M4.

the other important point for us is the room temperature.
it seems to be set at 25.5°C or something like that.
it's much too high.
Aurélien, who is the person to contact to change this temperature?
a setting around 21°C would be much more convenient...

• We changed the mirrors position back to the original reference (0, 0, 0, 0) for all mirrors, but the alignment could not be found.
• The course of action will be :

                      -  abandon the alignment done previously with Helium Neon Laser

                      - Set and distance between the spherical M3-M4 to a value that stabilizes the cavity, and keep the distance between the planar at zero reference.

                      -  Align the cavity from the start with the koheras

                      - after finishing the alignment, change the distance between the planar mirrors M1-M2 mirrors to match the rep. frequency 876.3636 MHz 

                           While maintaining the alignment.

Today, the vacuum pressure inside the Minicav was good : 7.8e-6 mbar
the Gauge model is a Leybold PTR 90N => see picture for details
surprisingly, the same gauge connected to the TurboVac SL 80 was not read with the same value (see pictures)
the Pfeiffer pumping system has its own gauge which gives an expected lower pressure value : 8.94e-7 mbar.

we made a leakage test with the cavity valve closed:
we lost 0.2e-6 mbar in 15s which is roughly equivalent to 1e-3mbar in 20h !!!

we made also a test of locking with the pumping system ON:
the silent block works pretty well and the locking doesn't seem perturbated.
(air flow OFF and no talking during the lock)
we clearly saw a sensitivity of the lock to the laser power => we can think to a feedback loop on the laser power with and AOM for example.

************************** The work in this report is done in the Minicavity clean room ***************************

Location: Minicavity Clean Room

1. On 14/01/2021
   • Installation of the minicavity base (reference plate) (First attempt)
   • People: Yann, Carmelo and Manar (Guided by Aurélien from afar)

   • There was an issue with the holes for the screws (they were smaller than the original design)

2. On 26/01/2021
   • Installation of the minicavity base (reference plate) (Second and Last attempt)
   • People: Yann, Manar (Guided by Aurélien from afar)
   • The arrival of the new corrected plate. Installation went smoothly without issues.
   • **** Note: Need to check the correct placement of the plate.
3. On 01/02/2021
   • Update on the status of the plate
   • a picture of the placement of the plate is attached, it shows that it needs adjustment
   • a schematic of the plate is attached
     The plane mirrors must be spaced 88 mm apart and the spherical ones are 88.7 mm apart.
   • ****note: the cables for the motors are not connected yet. 

*****Note: The phone was cleaned thoroughly with the duster and ethanol before taking it into the clean room.

The reference plate position was adjusted;

- previously: the side facing us (where the plane mirrors are located), the distance between plane mirrors was smaller than spherical. 

- now: its position was reversed, the distance between the plane is grater than spherical.

***A good way to always notice this immediately is the marker (pointed in the red circle) at the top left in the picture attached.

The plate should always be placed in a way that the marker should be located on the spherical mirrors side on the left away from us.

The minicavity mirror mounts are located in the preparation room  before the clean room in the cupboard.

There are three mounts and two primary mounts for the mounts to be placed on.

Need another one to have a set of four --→ They are made specifically by the lab, order extra one

The mirrors have what seems to be damage spots on them

To be investigated after finishing the alignment 

attached a picture of the mirror (To show the mirror size scale)

There are spare mirrors placed in the preparation room of the minicavity

the exact number to be investigated

approx ~ 12  -→    9 of them are injection  

Specific length (5 mm) for the screws used to fix the mirrors and the irises in the cavity box

need to search for extra, don't have enough

the amount needed  (3 x 4 = 12) at least, each mirror is fixed with three screws

As shown in the image attached when placing the mirror mounts (or irises) of the very close mirrors on the mounts they hit each other. 

The motor's location needs to be changed for them not to hit each other (pushed a little to the back or the front)

This restricts the motion of the motors later on.

Not sure if this was the case before changing the plate or only after

The mirrors were placed in the wrong orientation, it was adjusted correctly

but the issue of having the mirrors/irises hitting each other was still there.

The motors need to be moved in the longitudinal position to avoid this issue.

Throughout all the range of motion for the motors  

-→ no problem with the mirrors close together (M1-M3 and M2-M4) hitting each other.

-⇾ the problem with the pinholes hitting each other was fixed by trimming their edges a little, no issue for M1-M3 and M2-M4 now. 

The beam waist of the Koheras CW laser after the collimater is bigger than the Waist required for injection inside the cavity at M1.

A Telescope is to be made to match the two beams.

Details will be added ......

The telescope to adjust the beam size was made only using one lens with very long focal length (1 meter)

it is placed a distance of 40 cm from the collimeter and 1 meter from the center of the beam waist between the planar mirrors.

This way the two beam (of laser and cavity) have the shape when they propagate

(                              )                                /-----------()------- 40 cm ----------(collimater)_______[Koheras]

                                                                |

\                w|--------------/-------100 cm -------------/

The placement of the new ordered optical joint for the minicav

A new optical window was installed in place of the old broken one (it was broken from the sides, a sign there might have been a leakage before !!! )

The old broken window is placed in a container in SAS room in the gray cupboard titled "old window broken on the side"

The one changed is the output window behind M2 and M4

Properties of the new window attached

Update, they are received and the order is logged in MINICAV orders

Mounts placed in SAS cupboard

Enclosed is the current setup of the minicavity

** made by Fred