The scattering of green beam

After adjusted the waveplate and the EOM, we adjust the Faraday Isolator today to get more power transmit. Now more than half of the power can reach the cavity.

There are some problems we need to fixed,

1. The crystal is not fixed, when we try to get the mode matching, sometimes cannot avoid touch the cavity, then we lost everything. Matteo did the alignment many times in few hours working.

2.There are too many green reflected back, the maximum efficiency we got is about 17%, with a input infrared power of 670mW, and output green of 119mW, when the cavity is locked. But there are at least four reflect green beam on the mirror before the dichoric mirror, we are able to measure two of them, one has 1-2 mW power, the other has 4mW.

3. The green beam has some fringe on it, so this maybe means there is not only one green beam come out from the cavity, but we are not sure.

After first time we got a efficiency of about 16%, we break the lock and wait for twenty minutes to see if the system is stable or not. When we try to lock it again 20min later, the output of green is almost the same with some tiny re-alignment.

Optical setup for JASMINE scatterometer

I finished the configuration of the optical setup for our hemispherical scatterometer Yesterday.
The beam of the new laser is now focussed to a beam diameter of ca. 0.32 mm at the sample's surface.

However, I think there are still things that need to be done:

A diagram of measurements of the beam's profile is shown in the attachment. It shows the measured values of the profile without a focussing lens (circles) and with a lens at 430 mm distance to the collimator (stars). The actual distance of the lens in the setup is, however, 490 mm. Due to a small mistake, I underestimated the distance to the sample a little bit and had to readjust the positionof the lens.
Anyway, as can be seen, the measured values are in consistence with the calculated ones (dotted curves) only until the waist has been reached. With increasing distance again, there is a considerable difference between measured and theoretical value of the beam's radius*.
I think I have to measure again and try to find out the reason of the difference.

*The values are related to a Gaussian fit of the beam's cross-sectional intensity and represent the diameter of a Gaussian curve.

BS mirror

Yesterday we found out that the BS mirror is pretty sensitive to the polarization. From p to s polarization, the transmit part can change from 10% to 2% (it is a 90:10 BS mirror). Mirror is BSX17 from Thorlabs. Below is the website:

https://www.thorlabschina.cn/newgrouppage9.cfm?objectgroup_id=4808&pn=BSX17

And we test the cable which can send signal from end room to the central room, we followed the cable to the end room, found a same box as in the central room, send a sine signal from there and got the signal with the oscilloscope in the central.But in the west end, we could not find the box, but I think we will not use that arm.

Picomotors connection

On Friday, Manuel and Takahashi-san went to TAMA and sucessfully tested picomotor controller connection. Here a summary of what I have understood about this:

 

In order to make the computer be able to comunicate with the picomotor controller they must have the same IP address (except for the last digits).

Controller should have a static iP address and for this reason cannot be connected directly to NAOJ network (since it doesn't allow a static IP address). We have to choose a port in the  getaway which are isolated from NAOJ network (and disconnetected from the internet).

The network used for the optical lever control is one if the and can be a good choise. The relative IP adreddes are of the form 133.140.121.XX.

The ports relative to this network in the gataway that can be found up-left corner in tama central room are the number 1 and 2 (see pictures 1 and 2). 

 

The steps to establish the connection :

1) Pick a gateaway port which is isolated from the naoj network (disconnected from the internet) and  find  the relative IP addreses

2) Using serial port assign to the controller a proper IP address ( command IPADRR )

3) The proper IP address has to be the same of the network except for the last digits which has to be not yet assigned ( make a ping to check..)

5) Also the pc IP adress should be check and eventually changed (with the " assign manually option") to a proper one. (Same of the network with different last digits)

6) Connect both the PC and the controller to the same network and try the ping

[NB if we are not interested in being connected to a network we can simply connect the pc and the controller to the same switch and manually assign them a compatible IP address. In order to connect the PC directy to the controller a crossover cable is needed ]

Comment to picomotors connection issues (Click here to view original report: 396)

following Takahashi-san's advice I connected PC, controller and network cable to the same Ethernet hub. The ping still fails. BUT if I unplug the nework cable, which means I isolate my system from NAOJ network, then I get this ping returns:

Pinging 10.68.10.241 with 32 bytes of data:

Reply from 133.40.117.65: Destination host unreachable.

Reply from 133.40.117.65: Destination host unreachable.

Reply from 133.40.117.65: Destination host unreachable.

Reply from 133.40.117.65: Destination host unreachable.

Ping statistics for 10.68.10.241:

      Packets: Sent = 4, Recieved = 4, Lost = 0 (0% loss),

In the case of 192.168.11.121-IP controller the ping still fails, even in the isolated case.

Comment to picomotors connection issues (Click here to view original report: 396)

I found that NAOJ network uses DNS, so I follow the instructions of "Ethernet Configuration Example 2" at page 50 of the manual. (last time we tried Example 1 and, apparently, it didn't work because of DNS).

Through serial port, the IPADDR command returns 192.168.11.121 for one controller and 10.68.10.241 for the controller labeled NM2.

I connect the controller with IP address 192.168.11.121.

HOSTNAME command returns: nf8752-295333

I change the hostname with the command HOSTNAME NF8752-001

Save the configuration with the SAV command

RESET

Try to ping NF8752-001, failed (it says: "Ping request could not find host NF8752-001")

Green power and the effciency

I upload two figure, the first one is the green power as a function a infrared power.Both in the two figures, the infrared power was measured just before the cavity, and the green is measured in the transmit path of the dichoric mirror. This is the result after I adjusted the EOM and BS mirror, so I got a maximum power of green over 60mW.

In the second figure, the y-axis is the green power over infrared power, I just want to show the efficiency of infrared change into green at different input power.

I already changed the dichoric mirror from Thorlab two inch one into CVI one inch mirror has a anti-reflect coating on the back side can reduce the amount of power reflect by it. Still doing the alignment with the new mirror.

picomotors connection issues

In the past days we made some tests in order to check the communication between the computer and the picomotor controller.

Details on the picomotors drivers can be found in the user's manual at this link:

http://164.54.212.3/control_systems_manuals/87XX_Manual_RevC.pdf

We followed the instructions to configure the ethernet connection at page 48/50 of the manual but we didn't succeed in setting the communication.

We did the following steps:

1) Connect a PC to the serial port and send a IPADDR MCL command to get the IP address of the controller. For the controller named NM2 we got the IP 10.68.10.241.

2) Connect the controller and the computer to the same ethernet network in TAMA and try to ping the drivers from the pc without success.

3) Since we are convinced that the IP we got is not the good one to connect to TAMA newtwork ( all the other adresses are of the form 133.40.XXX.XX) we tried to ask the IP adress (again by using serial port) after having connected the drivers to the ethernet but we got the same answer.

We probably need the advice of a TAMA network expert in order to fix the problem.

Crystalline coating roughness

We have 2 crystalline coating samples from CMS company, one attached on a silica substrate and one on a sapphire substrate.

I plot the surface roughness of the crystalline coating samples we measured at LMA.

I calculated the PSD of the surface profile.

Progress of Feb 28th

I removed the EOM and checked the polarization, if not there is not enough space for PBS. The total power inject onto the PBS is 768mW, and the reflect part is 764mW, so I think this is enough to prove the polarization is S.

Then I put the EOM back and adjust it to a good position, also change the move the BS mirror a little bit for not let the beam goes too closed to the edge. After these, I do the alignment again and get pretty good mode matching.

I changed the laser power, to see with different amount of infrared what is the efficiency of the green production. And at one infrared power I measured the green beam with different SHG temperature, and found the best phase matching temperature. I tried to make a plot, but found at there are two points are not very reasonable, I will measure it again tomorrow to see if the problem comes from the measurement.

Some problems found today

The first problem is that I found out the upper part of the cavity(pointed by the arrow in the picture) can be moved, and if I twist a little bit in counterclockwise to maximum, I will get TEM00.

Then the EOM is very sensitive, even touch it can change the transmit power. There are some possibility, one is while touching, the alignment changed, the other one is there are some electric effect, but not quiet sure about this guess. Or it maybe caused by the polarization before the EOM.

So I will check the following things: the alignment of the EOM, the polarization between the laser and the EOM.

Checking the alignment of EOM is also because we lose too much power there, and also between the waveplate, I have already check the waveplate all have AR coating. At the very beginning of the experiment, I checked the transmission rate of the Faraday Isolator and EOM are both less than 90%.

There are also a small problem with the BS mirror, the beam is near the edge of the mirror which will lead to more scattering. So I will also adjust the position of it.

Status of vacuum system in South arm of TAMA

I checked the vacuum system for South arm in TAMA on 20th.
The 300m arm tube is in vacuum, 71mTorr at the South End and 92mTorr at the Mid point.
Three TMPs (Near, Mid, and End) along the arm can work with the rotary pumps (RPs).
We can start to evacuate the tube without initial pumping by a large RP.

The next step;
1) Start evacuation.
2) Check the penning gauges in HV (<10^-4 Torr).
3) Check the ionization pumps (IPs) in UHV (<10^-7 Torr).

Infrared power

I add a figure for better understanding the infrared power at each position.

Uncoated half ball glueing test

before gluing the coated spherical mirrors to the 1"-support, I made a test with an uncoated one. It is cured with UV light, so I put it under a neon light wich have a small part of UV. The higher the UV intensity, the faster the cure, so now I have to wait some days for curing and bonding.

Polarization and power

I checked the polarization with PBS, found out that we are using the p in infrared and s in green.So the dichoric mirror should be changed.

Then I checked the infrared power at different position with less output power of laser.The result:

Laser-(808.3mW)-waveplate-(795.5)-waveplate-(794)-Faraday Isolator-(728.4)-waveplate-(650)-EOM-(517)-BS mirror-\(429.4)-(399,6)-lens1-(331.9)

-mirror/-(323.2)-lens2-(307.9)-waveplate-(303.0)-lens3-(299.2)-mirror\-(293.7)-dichoric mirror-/-(292.8)-SHG

Between the BS mirror and the lens1, the power seems reduce with the distance.

And after checked the power, I found out I lost the alignment seriously. No matter how I change, the TEM00 cannot get larger. I think I did not move the cavity, but I cannot find other reason for this situation.

Check the power (part of)

After the ATC people return the table leg back, I found out I need to the alignment again. But after I finished it, tried to get some data of the infrared power. I found out the table was not put back in a good position, when I pushed on one corner, the other side will lift. So Manueal helped me to fixed the table more, and of course I need to adjust the alignment once again after it. I forgot to check the table is horizontal or not, I will do it tomorrow.

So until now I only checked power of half beam path. But it does not seems very reasonable, so I will reduce the power and do it again to check.

I checked the polarization, we are using the S polarization in infrared and get P polarization in green. The dichoric mirror we are using now is HBSY21 from Thorlab, which has a better performance in S polarization in reflection and better in P in transmission. Below is the website for more information:

https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=7035&pn=HBSY21

The green power now is about 46mW which measured after the dichoric mirror, and since I cannot put a power meter in the beam path, so I tried to measure the green beam which is reflected by the back surface of the dichoric mirror, and it is separated from the input beam,so I could measure it without block the infrared. And the power of this beam is aobut 4mW. But I need to check about other information of the back surface of the mirror.

Comment to Check the phase matching temperature (Click here to view original report: 385)

- Indeed the Pound-Drever signal looked strange.
Out of the resonance is very close to zero as it should. So there is no large electronic offset.
On one side of the resonance the signal is positive and looks relatively normal.
But on the other side of the resonance it's only slightly negative and when the cavity is at
resonance the signal is positive. A picture would have helped this explanation.

- When the cavity is at resonance we measured about 65 mW on the green beam coming
from the SHG and transmitted through the dichroich mirror. It would be nice to see how much
IR power we are injecting into the SHG cavity. It would also be interesting to see how much
green light is not transmitted by the dichroic mirror to have a full picture.

Change the PD

Today we changed the 15MHz tuned PD, which is also more sensitive to infrared than the one we used before(Thorlabs PDA36A).

After the readjustment of the beam, we got a better error signal than before, about 100mV peak to peak and also the positive and the negative part are almost the same.

With this error signal, we try to lock the cavity but it seems the signal is wrong. After changing the modulation phase, we locked the cavity and it last longer time.

But even with the new PD,there is still the 'jump' when goes near the resonance, so we get rid of another possible reason.

The next step is try to get the transfer function of the loop to see more details.

Check the phase matching temperature

I found the green beam power as a function of the cavity temperature while scanning the cavity with 28Hz triangle wave. And the result shows in the first figure. Compared to the figure we got without the miniscope, it looks different.

Since directly we cannot see the temperature, the peak of the figure has the resistance of 3.265 kiloohm.

And in the following three pictures, the beam shape changes while the temperature change.

The second and the third pictures show that the beam start to get strange, inside this range, the beam basically is a spot, but as the temperature goes away from the maximum, there are more things around the spot.

We did some test today find out the reason why there is asymmetric of the resonance peak.

1.Set the temperature back to near room temperature, when there is no green light produced. In this way, we get rid of the effect of the green beam. But the asymmetric does not change much.

2. Change the laser crystal temperature, still nothing change.

We did not find the reason for the asymmetric, and also from the error signal, it seems there is some offset, but did not very clear where it comes from. I will change the PD to the one more sensitive to the infrared and with the 15MHz tuned.

Filter cavity servo preparation

I attach some slides where I have summarized the work done to prepare the filter cavity servo.

In the second attachement there is a computation of the optical gain of the cavity.