Author Topic: Keeping our kHz laser at the right temperature  (Read 2577 times)

April 11, 2017, 11:47:27 AM

Matt Wilkinson

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Keeping our kHz laser at the right temperature
« on: April 11, 2017, 11:47:27 AM »
Hi all

From about the beginning of 2017, the team at the SGF noticed some increased instability in our terrestrial range calibration values at the level of 2-3 mm.  It was particularly clear on the first calibration of the day being a low value and so we learnt to take at least two calibrations before starting an observing duty.

2 weeks ago we also saw an increase in the RMS of the calibrations and some periodic behaviour in the calibration range values.  We consequently took the kHz laser offline and began using our older 10Hz laser, which had very stable calibration values and RMS.

After some investigation and discussion with High-Q, the team found that the flow rate of the cooling water was much lower than it should have been.  The water used is a reservoir of distilled water, but after 10 years of use something had built up to block the waterways.

Temperatures in the laser bed were not being kept at a stabilised constant, causing energy fluctuations and range errors from the start diode. The temperature would change when the laser began firing after being off for a period (20+ minutes). It would stabilise after approximately 10 minutes, during which time calibration range differences were seen.

Running the flow backwards and using a descaler (Durgol was recommended) brought the flowrate up to specification levels.  Setting the best operating temperature removed the signals in the range values and now the calibration RMS and repeatability are now within acceptable levels.

Needless to say, we will be checking the flowrate more often from now on.


September 20, 2017, 09:35:50 PMReply #1


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Re: Keeping our kHz laser at the right temperature
« Reply #1 on: September 20, 2017, 09:35:50 PM »
Hi Matt,

We hardly ever have our laser not firing and very very rarely stop the water flow through the table but our start diode is possibly subject to temperature fluctuations since it is on the side near the air conditioning vent. Although we monitor table temperatures closely, I don't monitor anywhere near the start diode. I will install a thermo-couple on the diode housing today! Now that we are on our event timer, we can see much more subtle changes in system delay, so I am really on the hunt  for these little things - thanks.


October 11, 2017, 03:33:04 PMReply #2

Sven Bauer POT3

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Re: Keeping our kHz laser at the right temperature
« Reply #2 on: October 11, 2017, 03:33:04 PM »
We have a laser system similiar to HERL station. Even though we use purified water we have to clean the cooling circuit of our laser every few month. We will start to monitor the water flow in the tubes to see if too much deposits are reducing the flow and with that the cooling as well as the laser power.
We were talking to a technician from the company who said that the inside of the laser the pipes are made of Aluminium which probably reacts with the purified water ... generating white deposits that start to collect and block the pipes. Not much we can do about it except monitoring and cleaning. Descaler helps to remove the deposits quite well.

May 30, 2018, 01:40:18 PMReply #3


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Keeping our laser and electronics temperature
« Reply #3 on: May 30, 2018, 01:40:18 PM »
We are installing in Riga a network of SLR temperature sensors using RapsberryPI's and the software in Python.
One RapsberryPI with 2 sensors is monitoring the laser room (where the 25 meters calibration path single mode optical fiber is stored) and another sensor is on the PMT thermal box attached to the Telescope receiving Coudé path (on open air when tracking) but connected to the Laser Room sharing the heating/cooling.

The second RapsberryPI with 2 sensors is monitoring the Control/Electronics room and the CFD/Event Timer electronics

Here is a plot of the daily max/min temperatures at the PMT box