Jared lab notebook

--Jmiles2 (talk) 12:39, 13 May 2014 (CDT)

I need close to 17 mW of seed power for the 2nd FORT beam to work at 2 Watts. Although this is is in the range of acceptable powers for this TA I still want to contact M2K lasers and make sure the Intensity is not too high. I can only get about 40% through the AOM when powering it with 2 Watts. I get around 33% out of the fiber at higher power (~600 mW). I get over 200 mW from the output of the fiber.
Need two AWG outputs for evaporative cooling of both FORT lasers. For the FPGA, FORT on/of Channel 14, is a switch to the FORT 1 amplifier, and turns it on or off. The RF in to the amplifier is controlled by the AWG which is triggered from CHannel 10, FORT AWG. OFF means the AWG is triggered.

--Jmiles2 (talk) 14:25, 14 May 2014 (CDT) For the AWG/hittite chip on FORT 1, 3db input on CW setting is equivalent to 33 to 33.2 dbm output power, 2 Watts, maybe a tad more. Since I'm not running this all the time, I think slightly more than 2 Watts should be fine. On pulse setting, 0 V input gives 11.5 dbm and -700 mV gives 32.8 dbm. A little over 20 dbm attenuation, that should work fine for what we're doing. The majority of attenuation happens from 0 to -200 mV.

I made an identical circuit for FORT 2. at 0 V, the output is 33 dbm for 4.5 dbm input power. The input power might change based on what RF generator you use, always check it first. At 700 mV the output is 4 dbm, 29 dbm range, I think the circuit for regulating the current to the chip is slightly off in the FORT 1 circuit. 4 dbm input give 33 dbm at CW setting.

--Jmiles2 (talk) 11:05, 15 May 2014 (CDT) Need to get FORT 1 laser to one polarization. Alignment affects polarization, looks like most of the light is vertically polarized. 19 amps give me 20 Watts in vertical direction. ~20 Watts is max for the AOM. Put in a wave plate to change to horizontally polarized so it would go through the beam cube. Still get good efficiency through beam cube, 45% to 50% at high powers. I get a little over 7 Watts after the beam cube.

FORT 2 is now aligned to the MOT. I can get atoms trapped with either FORT now, they are aligned over top of one another and I can load FORT 2 from the atoms in FORT 1, with no MOT. Need to check lifetimes of both.

--Jmiles2 (talk) 16:14, 19 May 2014 (CDT) Lifetime of FORT 1 is now much longer than it used to be. I'm not sure why, but it might be because the laser power is not jumping around as much. It was moving around by as 20% on the photo diode when evaporative cooling at the end of March. The only thing that is different is that I have the laser going through a beam cube, and have optimized the alingment so that the Horizontal linearly polarized light is maximized at ~18 Amps of laser current. 18 to 19 amps should be operating current, around 20 Watts on the AOM.
Taking different temperature measurements for different evaporation times, up to ~400ms.

--Jmiles2 (talk) 10:09, 21 May 2014 (CDT) Lifetime data from Both FORTS. Lifetime Data Fort Lifetimes. Green is the high power FORT around March 2014 and Black is the same FORT in May 2014. Red is the TA FORT, also taken in May 2014.

--Jmiles2 (talk) 17:17, 24 May 2014 (CDT) Put a shutter after the TA for the MOT beams. This improved the lifetimes by around 150 ms. Can get temperatures equivalent to ~16 nm/us. I should do a temp scan with more data points, around 10 to get a more accurate number. All of the temp measurements with the 1064 FORT have 200us exposure time.

--Jmiles2 (talk) 18:13, 30 May 2014 (CDT) Coupling beam on resonance 204.5 Mhz. Probe resonance at 220 MHz. No EIT yet. I think it's a laser issue, this happened about a month ago when I tried to get EIT with the 1064 nm FORT. I'll do the threshold test on the laser and find the peaks again, maybe put it through the interferometer.

--Jmiles2 (talk) 18:18, 9 June 2014 (CDT) Need to find EIT again. Polarization might be an issue, need them to be opposite linearly polarized I think. Only using the Large FORT laser to trap atoms. Peaks look fine on the laser, and linewidth seems reasonable. I could try another diode, but I don't why I'm not seeing anything :(

--Jmiles2 (talk) 14:17, 12 June 2014 (CDT) EIT works, although the transfer should go to zero at high control powers, it seems to go back up at much higher powers, ~50mW control with 15 mW probe. beam sizes around 1mm. I can check my background better by looking at the two spots where I add together the pixels with no FORT. Subtracting these two should give me zero but there will be some small error in this.

--Jmiles2 (talk) 18:01, 16 June 2014 (CDT) I can get EIT on both beams, and they both do basically the same thing, the curves aren't exact, but they never have been. The second EIT pulse looks slightly different than the first but the most transfer still occurs around 3mW. I think the standing wave is working but it isn't consistent. There is a pattern there, but it's much noiser than ones that I have seen before.

--Jmiles2 (talk) 12:42, 20 June 2014 (CDT) Can't get a good standing wave pattern, even though EIT curves look good. I think it might be something with the FORT. It's possibly too inconsistent to see the small change (~20%) I need to see in the standing wave patter. I looked at scans of the Large FORT yesterday and it looks like the signal was oscillating much more than it was when I did EIT before with the D1 line with the 850 nm FORT. I'm going to try to get the 1064 TA FORT working so I can see if the signal from those FORT atoms is more stable.

--Jmiles2 (talk) 10:19, 23 June 2014 (CDT) Need to watch the power out of the TA, I think something might be wrong. Today I have 12.8mW input power and 1.41 Out at 3.106 Amps. I thought I was getting more a few days ago. I also think I need a longer focal asphere to better couple to the TA. I have a very short focal length asphere right now.

--Jmiles2 (talk) 18:35, 24 June 2014 (CDT) I'm going to work with the TA_FORT for now. I can get some evidence of standing waves with either FORT laser, but the better data was taken with the TA FORT. I'm going to look more into the statistics of my measurement. This could be a problem that I haven't addressed up to this point. The standing wave hasn't always worked in the past, the one Think that I thought fixed it was a loose mirror, but I was never sure that was the case. The standing wave shouldn't be that hard to get though, once it works, it usually stays working fine for awhile, over a month.

I get a decent signal with the TA FORT with only ~220 mW of power. The beam size could be expanded bigger to make a deeper trap.

--Jmiles2 (talk) 10:37, 26 June 2014 (CDT) I think noise might be a problem. I started looking at the fluorescence from the MOT with a photodiode. The signal oscillates at around 120 Hz, the same frequency that the feedback to the laser piezo is oscillating, I think this is changing the frequency of the beam slightly and a different number of atoms is loaded into the MOT. It would also change the number of atoms I detect in the FORT because I use the same laser to look at the fluorescence of the FORT atoms with a photodiode.

--Jmiles2 (talk) 15:56, 27 June 2014 (CDT) Noise in the FORT atoms go down when I turn up the gain on the MOT seed laser. There is a standing wave, but I can't get a good plot that shows more than one peak. I think this is the same problem I've had before but never quite figured out what was wrong.

The TA before the second High frequency seems very sensitive to alignment. Over the course of the day it got unaligned, and I had some trouble getting it back, about 265 mW out of that to get ~170 through the high frequency AOM.

--Jmiles2 (talk) 23:08, 1 July 2014 (CDT) Standing wave working much better now, up to 25%, not sure why. The last thing I did was realign the coupling beam from ChB on to ChC, it didn't seem to do much, the power I got through the fiber went from ~4.98mW to ~5.02mW, not much at all. I also did the threshold test on the seed laser again, it did improve it, but I didn't see a better standing wave immediately after. It also looks there is some asymmetry with the standing wave. I get different results whether ChC or ChB has the larger coupling beam power.

While things were working, I checked to see if the collection size (how many camera pixels I take as data) affected the percent difference between nodes and anti-nodes. I doubled the size and saw little difference.

I see a good standing wave with the Big FORT laser. Maybe some narrowing too. I might have even been using the wrong settings, I think I was using the saved state 9 on the delay generator instead of 8. They should both be very similar, so I don't think it's a huge problem, but I can't remember for sure which one I was using for the data I was taking, it should be 8 but I think it might have been 9 for some of it.

Either way, I still got really good contrast with the standing wave, and contrast with the larger FORT.

--Jmiles2 (talk) 15:55, 3 July 2014 (CDT) When the laser is pulsed, there is a different amount of power that gets through The AOM than when it is on CW. For Ch.C. the pulsed power is about 10% less that the CW power. For Ch.B. the pulsed power is about 5% higher than CW. This could cause some differences in what I set the power to. I want to check this every few days, because I think I'm getting slightly different numbers when I test it. I'm focusing the CW into a photodiode, and then switching to pulsed, seeing what the difference is. I got 15% instead of 10% for CH.B. yesterday...but I'll go with 10% for now.

It would be helpful if I could measure that pulse power by itself.

--Jmiles2 (talk) 14:02, 17 July 2014 (CDT) I still get a different signal depending on which coupling beam I have larger. I increased my signal to noise by using the binning feature on the camera. This combines pixels on the camera, making my signal about the same, but the noise that I subtract is now much less. The noise is more off an offset now, and doesn't affect the pattern that much. This also lets me go to lower power, which should reduce the Fort Temperature.

There are still other noise issues I'm not sure about. I might just have to accumulate more.

--Jmiles2 (talk) 16:45, 18 July 2014 (CDT) My signal is still noisy compared to the feature I want to see. [[1]]