Friday, August 10, 2007
Summer experiments
Tom Kennedy, my post-doc advisor at the Naval Research Lab, emailed me a couple of days ago and asked how the experiments were coming. I emailed him back some details. Since I don't talk about the specifics of my research to people very much (I worry about boring and/or confusing people), I thought I'd post my reply to Tom here, with just a couple of paragraphs removed. Hope Tom doesn't mind. This way people can read or skip over, as desired! :-)
If you don't understand all the terms, that's OK!
Acronym glossary:
ESR = electron spin resonance
NMR = nuclear magnetic resonance
ODENDOR = optically detected electron-nuclear double resonance
ODMR = optically detected magnetic resonance
PL = photoluminescence
___
Tom,
Experiments have been hectic, but have been going very well overall this whole summer. As you know, the first set of experiments were to test out our cavity using the InP sample for the ESR, and optical NMR with GaAs to test the nuclear coils. That all went smoothly. I plan to use that data along with details on the cavity construction, theoretical predictions of cavity modes, etc, in a Review of Scientific Instruments paper.
Then, we had good success doing ESR on the three main samples. It was almost too easy with the Kerr rotation technique! I kept telling my students that we were able to do in one afternoon something that you and I had tried unsuccessfully to do for at least 6 months! I'm still amazed that we can get quality data in 20 second-long scans! Anyway, in addition to the ESR, we had good success seeing nuclear effects, and were able to eliminate those nuclear effects using NMR. We were able to do ODENDOR, but with only mixed success--scans were not reproducible at all and I think we kept on getting caught in the age-old problem involving feed-back between the electrons and nuclei. That is, when we resonated the nuclei in the ODENDOR experiment, the electron resonance position would shift and (since the ESR signal is what we were detecting) blur the results. But we were able to (I think) get publishable data there too. If I recall correctly, we were even able to see the quadrupole splitting in two of the three nuclear resonances from the ODENDOR experiment. Also, by using the ESR resonance position to track the amount of effective B-field from the nuclei as a function of time, we were able to measure the nuclear relaxation time very convincingly (after first having polarized the nuclei to some extent). I think I'll be able to tie all of this stuff together into a single paper concentrating on ODMR with the nuclear effects.
The last couple of days haven't been nearly as successful, unfortunately. We tried doing the Kerr rotation ESR on two quantum well samples (14 nm QWs). We *may* have seen something with a g-factor of about 0.36, but I was by no means convinced. If it was present, it was extremely broad--and there was a lot of weird stuff going on in the background on one of the samples. So I've given up on that for the time being.
Tomorrow is our last day of experiments. Just for fun, we're going to try something completely different. I never was able to measure T1 of the 3E14 sample using the old PL polarization technique, because the probe pulse had to be so extremely weak. So, we're going to try doing this with Kerr rotation as the probe pulse. It'll require synchronizing two lasers and pulsing them both electronically--one circularly polarized that is above the bandgap, to polarize the electrons, and one linearly polarized that is just below the bandgap, to provide the Kerr rotation probe of the polarization status. Seems like it should work! But we'll see. [Note: it wasn't successful at all. C'est la vie.]
John
If you don't understand all the terms, that's OK!
Acronym glossary:
ESR = electron spin resonance
NMR = nuclear magnetic resonance
ODENDOR = optically detected electron-nuclear double resonance
ODMR = optically detected magnetic resonance
PL = photoluminescence
___
Tom,
Experiments have been hectic, but have been going very well overall this whole summer. As you know, the first set of experiments were to test out our cavity using the InP sample for the ESR, and optical NMR with GaAs to test the nuclear coils. That all went smoothly. I plan to use that data along with details on the cavity construction, theoretical predictions of cavity modes, etc, in a Review of Scientific Instruments paper.
Then, we had good success doing ESR on the three main samples. It was almost too easy with the Kerr rotation technique! I kept telling my students that we were able to do in one afternoon something that you and I had tried unsuccessfully to do for at least 6 months! I'm still amazed that we can get quality data in 20 second-long scans! Anyway, in addition to the ESR, we had good success seeing nuclear effects, and were able to eliminate those nuclear effects using NMR. We were able to do ODENDOR, but with only mixed success--scans were not reproducible at all and I think we kept on getting caught in the age-old problem involving feed-back between the electrons and nuclei. That is, when we resonated the nuclei in the ODENDOR experiment, the electron resonance position would shift and (since the ESR signal is what we were detecting) blur the results. But we were able to (I think) get publishable data there too. If I recall correctly, we were even able to see the quadrupole splitting in two of the three nuclear resonances from the ODENDOR experiment. Also, by using the ESR resonance position to track the amount of effective B-field from the nuclei as a function of time, we were able to measure the nuclear relaxation time very convincingly (after first having polarized the nuclei to some extent). I think I'll be able to tie all of this stuff together into a single paper concentrating on ODMR with the nuclear effects.
The last couple of days haven't been nearly as successful, unfortunately. We tried doing the Kerr rotation ESR on two quantum well samples (14 nm QWs). We *may* have seen something with a g-factor of about 0.36, but I was by no means convinced. If it was present, it was extremely broad--and there was a lot of weird stuff going on in the background on one of the samples. So I've given up on that for the time being.
Tomorrow is our last day of experiments. Just for fun, we're going to try something completely different. I never was able to measure T1 of the 3E14 sample using the old PL polarization technique, because the probe pulse had to be so extremely weak. So, we're going to try doing this with Kerr rotation as the probe pulse. It'll require synchronizing two lasers and pulsing them both electronically--one circularly polarized that is above the bandgap, to polarize the electrons, and one linearly polarized that is just below the bandgap, to provide the Kerr rotation probe of the polarization status. Seems like it should work! But we'll see. [Note: it wasn't successful at all. C'est la vie.]
John
# posted by John Colton @ 9:57 PM 
