Pulsed optically detected NMR of single GaAs/AlGaAs quantum wells

Light-induced Knight shifts inGaAs∕AlxGa1−xAsquantum wells

“…22 Furthermore, we had to be able to modify the laser irradiation during the experiment. For that purpose, the laser beam ͑from a titanium sapphire ring laser͒ was split into two parts, which could both be controlled independently with an acousto-optic modulator.…”

“…Nuclear spin transients were excited by a radiofrequency ͑rf͒ pulse with a duration of 6 s and a frequency of 9.971 MHz, close to the resonance frequency for 75 As. As described in an earlier paper, 22 the resulting signal is closely related to the free induction decay ͑FID͒, and the NMR spectrum can be recovered by Fourier transformation of the timedomain signal. Figure 1 shows a typical spectrum.…”

“…20 Some of the optically detected NMR techniques that have been used to overcome the sensitivity issues of NMR in individual heterostructures such as quantum wells and quantum dots cause severe broadending of the NMR transitions, 18,19 thereby obscuring the relatively small Knight shifts. These problems can be avoided with a more recently introduced experiment, 22 which uses optical pumping to increase the nuclear spin polarization as well as optical detection, but combines them with pulsed radiofrequency ͑rf͒ excitation of the nuclear spins to avoid power broadening: during detection, the nuclear spins precess freely, in the absence of an rf field. The Fourier transform of the optically detected free induction decay, therefore, shows the natural width of the NMR transitions and is ideally suited to measure small resonance shifts with high precision and accuracy.…”

An optical NMR spectrometer for Larmor-beat detection and high-resolution POWER NMR

“…6 Further dramatic sensitivity enhancements may be obtained by using the same electron-nuclear coupling for optical detection of the NMR signal. Various methods have been developed to encode NMR signals in the polarization of photoluminescence ͑PL͒, [2][3][4]6,12,13 in optical frequency shifts 7 or in Faraday rotation of a linearly polarized optical probe. 14 Here, we detail implementation and advantages of the PL-based Larmor-beat-detection ͑LBD͒ method.…”

“…5,8,9 To date, few detailed descriptions of ONMR instrumentation and procedures have been presented. 13,15 The goal of the present paper is to present the features of our apparatus that enable the unique combination of optical NMR with both LBD and POWER NMR imaging. Many aspects are equally relevant to alternate versions of optically detected NMR.…”