Bruce arrived around 8:30 AM and Shane around 8:45 AM. Weather conditions clear and sunny.
Today, we decided to replace the flashlamps in REAL's Nd:YAG laser even though the pair running had only 16M shots on them.
(Normally, a pair of flashlamps should provide 20M shots.). We decided to do it today since Bruce was planning on leaving and we wanted to be sure that the LabVIEW control system handled the change appropriately. Photo below is the pair of flashlamps removed.
We used a new pair of flashlamps with the following information stamped on the boxes: 203-0032, Lot# 1670836, 2014-10, Serial #1670836-009 and Serial #1670836-010.
Important Note: we struggled the remove the head for a long time due to not reading the instructions in the user manual carefully (see page 5-2). It is important to spin the thumbwheel screw CLOCKWISE to loosen to the head. This is the opposite of what one expects: counterclockwise to loosen.
Inspected the ends of Nd:YAG rod inside the laser head and they both looked perfect. Difficult to get picture of ends of the rod since the camera struggles to focus inside the recessed end of the head. Here is a photo of one end that shows the shiny surface of the rod indicating no debris or burns.
We installed the head with new lamps and discovered a water leak on the left (rear) bottom white plastic lamp retainer. Shane had noticed the new bottom lamp electrode did not fit snugly in the o-ring. Replaced both o-rings on bottom flashlamp (o-ring kit for Continuum Surelite III part number 507-0905) and leak stopped. For reference, photo below shows the black o-ring on the old top rod.
Shane noted shots on the laser when turning key back on: 409,107,460. (Note: 407107460/10/60/60/24 = 473.5 days of operation over life of the 20-year old laser.)
30-minute warm up (running flashlamps with shutter closed) was applied and started system at 11:52 AM PDT (18:52 UTC). We noticed the 1543 nm pulse energy down to 93 mJ and Shane observed red flashing (4-wave mixing?) on the inclusion in the 2" mirror downstream of Raman cell. The inclusion had grow since it was discovered on August 3.
Shut system off within 3 PPI scans (<510 shots). Called Scott Spuler in Colorado for consultation. He indicated he would charge extra for weekend service. A more careful inspection revealed: seed beam on IR viewing card looks fine indicating likely no damage to optics (prisms and windows) in Raman cell.
We concluded that changing the flashlamps had slightly changed the pointing of the Nd:YAG beam and that we should realign it with the seed beam. (We concluded that the reduction in pulse energy at 1.5 microns was due to incomplete overlap of the seed and pump.). We put the Nd:YAG in single-shot mode, held the 2" ceramic detector immediately downstream of the Raman cell, and adjusted the Nd:YAG beam on the upstream gimbal until it overlapped with the seed. Bruce did the adjustment and used the shorter micrometer and turned it about 1/4 turn. Unfortunately, no photo was taken to show the misalignment or overlap achieved. (It would be hard to photograph given the flash of the Nd:YAG on the ceramic.) Note for future: it would be super helpful to have more space (inches) between the end of the Raman cell and the 2" turning mirror in the big gimbal. It would also be very helpful to have a small camera dedicated to monitoring the health of that mirror.
Checked Nd:YAG water level in the reservoir inside the power and cooling unit.
At 1:14 PM PDT (20:41 UTC) we ran the system again (1.47 kV on flashlamps) and began to collect data. 1.5 micron pulse energy was a little too high for Scott's preference and Bruce increased the q-switch delay to 255 (instead of 237) to reduce energies slightly. Top plot below is Nd:YAG pulse energy and bottom plot is 1.5 micron energy.
Scott says we should aim for 135 mJ for longevity of the components.
We have been focused on the transmitter today and not paying as much attention to the weather. However, I can write that I have not seen any clouds, the winds are lighter than usual, and the visibility is very large and the particle count data appears to be down. Eastern panorama at 4 PM PDT:
GOES-18 visible satellite photo at 4:14 PM PDT:
5-minute mean wind speeds from the tall tower today ranged from 1-4 m/s. Directions much more erratic than yesterday.
In terms of "How far is the REAL seeing?", here is a screen shot of the LabVIEW display at 4:37 PM PDT:
Pierre's PPI images for raw SNR show it starting at about 30 at 200 m range. This is one of the poorest SNR days that I can recall.
Purple Air data for the sensor near the ISS confirms why: very low particle counts.
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Unknown User (shane)
Sunday, August 27.
Bruce arrived around 8:30 AM and Shane around 8:45 AM. Weather conditions clear and sunny.
Today, we decided to replace the flashlamps in REAL's Nd:YAG laser even though the pair running had only 16M shots on them.
(Normally, a pair of flashlamps should provide 20M shots.). We decided to do it today since Bruce was planning on leaving and we wanted to be sure that the LabVIEW control system handled the change appropriately. Photo below is the pair of flashlamps removed.
We used a new pair of flashlamps with the following information stamped on the boxes: 203-0032, Lot# 1670836, 2014-10, Serial #1670836-009 and Serial #1670836-010.
Important Note: we struggled the remove the head for a long time due to not reading the instructions in the user manual carefully (see page 5-2). It is important to spin the thumbwheel screw CLOCKWISE to loosen to the head. This is the opposite of what one expects: counterclockwise to loosen.
Inspected the ends of Nd:YAG rod inside the laser head and they both looked perfect. Difficult to get picture of ends of the rod since the camera struggles to focus inside the recessed end of the head. Here is a photo of one end that shows the shiny surface of the rod indicating no debris or burns.
We installed the head with new lamps and discovered a water leak on the left (rear) bottom white plastic lamp retainer. Shane had noticed the new bottom lamp electrode did not fit snugly in the o-ring. Replaced both o-rings on bottom flashlamp (o-ring kit for Continuum Surelite III part number 507-0905) and leak stopped. For reference, photo below shows the black o-ring on the old top rod.
Shane noted shots on the laser when turning key back on: 409,107,460. (Note: 407107460/10/60/60/24 = 473.5 days of operation over life of the 20-year old laser.)
30-minute warm up (running flashlamps with shutter closed) was applied and started system at 11:52 AM PDT (18:52 UTC). We noticed the 1543 nm pulse energy down to 93 mJ and Shane observed red flashing (4-wave mixing?) on the inclusion in the 2" mirror downstream of Raman cell. The inclusion had grow since it was discovered on August 3.
Shut system off within 3 PPI scans (<510 shots). Called Scott Spuler in Colorado for consultation. He indicated he would charge extra for weekend service. A more careful inspection revealed: seed beam on IR viewing card looks fine indicating likely no damage to optics (prisms and windows) in Raman cell.
We concluded that changing the flashlamps had slightly changed the pointing of the Nd:YAG beam and that we should realign it with the seed beam. (We concluded that the reduction in pulse energy at 1.5 microns was due to incomplete overlap of the seed and pump.). We put the Nd:YAG in single-shot mode, held the 2" ceramic detector immediately downstream of the Raman cell, and adjusted the Nd:YAG beam on the upstream gimbal until it overlapped with the seed. Bruce did the adjustment and used the shorter micrometer and turned it about 1/4 turn. Unfortunately, no photo was taken to show the misalignment or overlap achieved. (It would be hard to photograph given the flash of the Nd:YAG on the ceramic.) Note for future: it would be super helpful to have more space (inches) between the end of the Raman cell and the 2" turning mirror in the big gimbal. It would also be very helpful to have a small camera dedicated to monitoring the health of that mirror.
Checked Nd:YAG water level in the reservoir inside the power and cooling unit.
At 1:14 PM PDT (20:41 UTC) we ran the system again (1.47 kV on flashlamps) and began to collect data. 1.5 micron pulse energy was a little too high for Scott's preference and Bruce increased the q-switch delay to 255 (instead of 237) to reduce energies slightly. Top plot below is Nd:YAG pulse energy and bottom plot is 1.5 micron energy.
Scott says we should aim for 135 mJ for longevity of the components.
We have been focused on the transmitter today and not paying as much attention to the weather. However, I can write that I have not seen any clouds, the winds are lighter than usual, and the visibility is very large and the particle count data appears to be down. Eastern panorama at 4 PM PDT:
GOES-18 visible satellite photo at 4:14 PM PDT:
5-minute mean wind speeds from the tall tower today ranged from 1-4 m/s. Directions much more erratic than yesterday.
In terms of "How far is the REAL seeing?", here is a screen shot of the LabVIEW display at 4:37 PM PDT:
Pierre's PPI images for raw SNR show it starting at about 30 at 200 m range. This is one of the poorest SNR days that I can recall.
Purple Air data for the sensor near the ISS confirms why: very low particle counts.