Name: high resolution phonon-assisted quasi-resonance fluorescence spectroscopy
Uploaded: 2016-06-28T13:00:00
Description: Watch this Scientific Journal Video about High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy at JoVE.com

The authors would like to acknowledge Allan Bracker and Daniel Gammon at the Naval Research Laboratory for providing the samples being studied. This work was supported (in part) by the Defense Threat Reduction Agency, Basic Research Award # HDTRA1-15-1-0011, to University of California-Merced.

Note: The methodology described is specific to a particular software, although other software packages may be used instead.
1. Sample Preparation and Cool Down
<ol>
	<li>Fabricate the sample.
	<ol>
		<li>Grow the sample, using the Stranski-Krastanov growth method via molecular beam epitaxy creating two vertically-stacked self-assembled InAs/GaAs QDs that are separated by a 4 nm tunnel barrier as previously described.16 Embed the QDs in an electric field effect structure (i.e.<...

<ol>
	<li>Germanis, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Piezoelectric+InAs/GaAs+quantum+dots+with+reduced+fine-structure+splitting+for+the+generation+of+entangled+photons.">Piezoelectric InAs/GaAs quantum dots with reduced fine-structure splitting for the generation of entangled photons.</a> Phys. Rev. B. 86, 1-4 (2012).</li><li>Valenti, J. A., Fischer, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectroscopic+Properties+of+Cool+Stars+(SPOCS).+I.+1040+F,+G,+and+K+Dwarfs+from+Keck,+Lick,+and+AAT+Planet+Search+Programs.">Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs.</a> ApJ. 159, 141-166 (2005).</li><li>Oetiker, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Searching+for+Companions+to+Late+Type+M+Stars.">Searching for Companions to Late Type M Stars.</a> .Astro. Soc. Pac. Conf. Ser. 212, (2000).</li><li>Seguin, R., Rodt, S., Schliwa, A., Potschke, K., Pohl, U. W., Bimberg, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Size-dependence+of+anisotropic+exchange+interaction+in+InAs/GaAs+quantum+dots.">Size-dependence of anisotropic exchange interaction in InAs/GaAs quantum dots.</a> Phys. Status Solidi B. 243 (15), 3937-3941 (2006).</li><li>Belhadj, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlling+the+Polarization+Eigenstate+of+a+Quantum+Dot+Exciton+with+Light.">Controlling the Polarization Eigenstate of a Quantum Dot Exciton with Light.</a> Phys. Rev. Lett. 103 (1-4), (2009).</li><li>Ulrich, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+single+quantum+dot+emission+characteristics+and+fine+structure+by+lateral+electric+fields.">Control of single quantum dot emission characteristics and fine structure by lateral electric fields.</a> Phys. Status Solidi B. 246 (2), 302-306 (2009).</li><li>Vamivakas, A. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+spin-dependent+quantum+jumps+via+quantum+dot+resonance+fluorescence.">Observation of spin-dependent quantum jumps via quantum dot resonance fluorescence.</a> Nature. 467, 297-300 (2010).</li><li>Poem, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polarization+sensitive+spectroscopy+of+charged+quantum+dots.">Polarization sensitive spectroscopy of charged quantum dots.</a> Phys. Rev. B. 76, (2007).</li><li>Flagg, E. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resonantly+driven+coherent+oscillations+in+a+solid-state+quantum+emitter.">Resonantly driven coherent oscillations in a solid-state quantum emitter.</a> Nature Phys. 5, 203-207 (2009).</li><li>Scheibner, M., Bacher, G., Forchel, A., Passow, T., Hommel, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spin+Dynamics+in+CdSe/ZnSe+Quantum+Dots:+Resonant+vesus+Nonresonant+Excitation.">Spin Dynamics in CdSe/ZnSe Quantum Dots: Resonant vesus Nonresonant Excitation.</a> J. Supercond. Nov. Magn. 16 (2), 395-398 (2003).</li><li>Faelt, S., Atature, M., Tureci, H. E., Zhao, Y., Badolato, A., Imamoglu, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strong+electron-hole+exchange+in+coherently+coupled+quantum+dots.">Strong electron-hole exchange in coherently coupled quantum dots.</a> Phys. Rev. Lett. 100, 1-4 (2008).</li><li>Vamivakas, A. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strong+Extinction+of+a+Far-Field+Laser+Beam+by+a+Single+Quantum+Dot.">Strong Extinction of a Far-Field Laser Beam by a Single Quantum Dot.</a> Nano Letters. 7 (9), 2892-2896 (2007).</li><li>Scheibner, M., Economou, S., Ponomarev, I. V., Jennings, C., Bracker, A., Gammon, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-Photon+Absorption+by+a+Quantum+Dot+Pair.">Two-Photon Absorption by a Quantum Dot Pair.</a> Phys. Rev. B. 92, (2015).</li><li>Palik, E. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Handbook of Optical Constants of Solids. Vols. I and II. , (1985).</li><li>Kerfoot, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optophononics+with+Coupled+Quantum+Dots.">Optophononics with Coupled Quantum Dots.</a> Nat. Commun. 5, 1-6 (2013).</li><li>Scheibner, M., Bracker, A. S., Kim, D., Gammon, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Essential+concepts+in+the+optical+properties+of+quantum+dot+molecules.">Essential concepts in the optical properties of quantum dot molecules.</a> Solid State Commun. 149, 1427-1435 (2009).</li><li>Bracker, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+electron+and+hole+tunneling+with+asymmetric+InAs+quantum+dot+molecules.">Engineering electron and hole tunneling with asymmetric InAs quantum dot molecules.</a> Appl. Phys. Lett. 89, 1-3 (2006).</li><li>Doty, M. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrically+Tunable+g+Factors+in+Quantum+Dot+Molecular+Spin+States.">Electrically Tunable g Factors in Quantum Dot Molecular Spin States.</a> Phys. Rev. Lett. 97, 1-4 (2006).</li><li>Stinaff, E. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+Signatures+of+Coupled+Quantum+Dots.">Optical Signatures of Coupled Quantum Dots.</a> Science. 311, 636-639 (2006).</li><li>Tkachenko, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Optical Spectroscopy: Methods and Instrumentations. , (2006).</li><li>Hecht, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Optics. , (2014).</li><li>O'Donnell, K. P., Chen, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temperature+dependence+of+semiconductor+band+gaps.">Temperature dependence of semiconductor band gaps.</a> Appl. Phys. Lett. 58, 2924-2926 (1991).</li><li>Stinaff, E. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polarization+dependent+photoluminescence+of+charged+quantum+dot+molecules.">Polarization dependent photoluminescence of charged quantum dot molecules.</a> Phys. Stat. Sol. (c). 5 (7), 2464-2468 (2008).</li><li>Jelezko, F., Wrachtrup, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+defect+centres+in+diamond:+A+review.">Single defect centres in diamond: A review.</a> Phys. Stat. Sol. (a). 203 (13), 3207-3225 (2006).</li><li>Doherty, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+nitrogen-vacancy+colour+centre+in+diamond.">The nitrogen-vacancy colour centre in diamond.</a> Physics Reports. 528 (1), 1-45 (2013).</li></ol>

The above instructions demonstrate the phonon-assisted quasi-resonance spectroscopy method. By exciting into a QD discrete state, one can monitor the phonon emission line, achieving high resolutions. In the example provided, by using phonons it is even possible to resolve the lifetime-limited linewidth of the neutral exciton visible in experiments. The method is easy to incorporate into existing PL spectroscopy setups. As mentioned, once the energy of the desired transition line is identified via non-resonant spectroscop...

High resolution is the key to unlocking new knowledge. With this knowledge, new technologies can be developed such as better sensors, more precise manufacturing tools, and more efficient computational devices. Generating this key, however, often comes at a high cost of resources, time or both. This issue is omnipresent across all scales from the atomic physics of resolving the lifted degeneracies of electron spins to astronomy where a small spectral shift can lead to detection of planets next to distant stars.1,2,3 
The focus of this work is on using a standard spectrometer setup and showing how it can resolve spectral features below its resolution limit, especially with regard to the field of semiconductor optics. The example presented is that of anisotropic electron-hole (e-h) exchange splitting in InAs/GaAs quantum dots (QDs), which is on the order of a few &#181;eV.4 The resolution limit of the spectrometer can be overcome by combining standard PL and laser spectroscopy techniques. This method of quasi-resonance fluorescence has the added benefit of achieving laser limited resolution using a commonplace single-stage spectrometer.
A standard optical spectroscopy system for single QD PL spectroscopy consists of a single-stage 0.3-0.75 m monochromator and a charge coupled device (CCD) detector along with an excitation laser source and optics. Such a system is at best capable of resolving 50 &#181;eV in the near-infrared spectrum around 950 nm. Even with the use of statistical and deconvolution techniques, such a single monochromator setup is not capable of resolving less than 20 &#181;eV in PL measurements.5 This resolution can also be improved by using a triple spectrometer, in triple additive mode, where the spectrum is successively dispersed by all three gratings. The triple spectrometer has the advantage of increased resolution, capable of resolving around 10 &#181;eV. In an alternative configuration, triple subtractive mode, the first two gratings behave as a band pass filter, giving the added feature of being able to separate the excitation and detection by less than 0.5 meV. The drawback of the triple spectrometer is that it is a costly system.
Before presenting the method of interest, we briefly discuss other experimental approaches that, with added complexity, achieve better spectral resolution and are able to resolve the fine structure of single QDs. Elements of these methods are relevant to the presented method. One such method is adding a Fabry-Perot interferometer (FPI) in the detection path of a single spectrometer setup.6 Using this method the resolution is set by the finesse of the FPI. Thus, the spectrometer&#39;s resolution is improved to 1 &#181;eV, at the cost of added complexity and lower signal intensity.7 The interferometer method also changes the general operation of the spectrometer with the CCD camera, effectively becoming a single point detector, and the tuning through various energies is achieved by adjusting the FPI cavity itself.
Resonance fluorescence (RF) spectroscopy, another method where a single optical transition is both excited and monitored also offers the promise of high-resolution spectroscopy. The spectral resolution is only limited by the laser linewidth and keeps the CCD as a multi-channel detector, where not just one sensor is detecting the signal but a number of CCD pixels. This multichannel detection is advantageous in terms of signal averaging. The challenge in RF spectroscopy is separating the PL signal from the larger background of the scattered laser light, especially when measuring at the single QD level. A number of techniques can be used to lower the ratio of signal to scattered laser light, which involve either polarization8, spatial9 or temporal separation10 of the excitation and detection. The first is to use high extinction polarizers to suppress the scattered light, but this method has the unfavorable outcome of losing polarization information from the PL.8 Another possible method to obtain resonance fluorescence is to engineer semiconductor systems that are coupled to optical cavities where the excitation and detection paths are spatially separated. This eliminates the issue of having to resolve the PL signal from the large laser background. However, this method is limited to intricate sample fabrication which is in general resource intensive.9
Another class of methods that is also able to resolve minute energy differences is that of pure laser spectroscopy, such as differential transmission, which has the benefit of achieving laser-limited resolution with complete polarization information. This method typically requires lock-in detection to observe miniscule changes in the transmission signal compared to that of the large laser background.11 Lately, advances in nanofabrication have led to a boost of the fraction of laser light that interacts with the QD(s) to values up to 20%, by either using index-matched solid immersion lenses or embedding the dots in photonic crystal waveguides.12
Even though these methods have the capability of achieving high energy resolution, they come at the cost of expensive equipment, complex sample fabrication and loss of information. The method in this work combines elements from these three methods without adding complexity in instrumentation or sample fabrication to a regular PL setup.
Recent work has shown that with a triple spectrometer system in subtractive mode, it is possible to visualize the singlet-triplet fine structure in the two-photon transition spectrum of a quantum dot molecule (QDM).13 The involved energy splitting on the order of a few to tens of &#956;eV were resolved using a triple subtractive mode, which allowed to excite the transitions resonantly and detect within less than a meV. The spectral information was extracted by monitoring below the transition using acoustic phonons and other lower-lying exciton transitions. This method can also be applied to resolve the anisotropic e-h exchange splitting and even the lifetime-limited linewidth of the exciton transition of 8 &#181;eV and 4 &#181;eV, respectively as seen in Figure 1. Similar to this result, this paper will focus on a simple spectrometer setup that will incorporate many of the advantages that the other high resolution methods possess. Additionally the CCD will remain as a multi-channel detector. The experimental setup can also be kept fairly inexpensive relative to other high-resolution spectroscopy methods and has the added benefit of being easily modified to achieve single point correlation measurements. Unlike the result using acoustic phonons and a triple spectrometer, the underlying key is to make use of the LO-phonon satellite associated with the semiconductors and related alloys that make up semiconductor samples. The energy separation between LO-phonon satellite and the zero-phonon line (ZPL) is on the order of tens of meV for such samples, allowing the use of a single-stage spectrometer.14 This energy separation allows for use of the proposed quasi-resonance spectroscopy method by resonantly driving a transition and monitoring below the excitation by an energy equal to one LO phonon. This technique is analogous to that of PL excitation where one excites into an excited transition and monitors the ground state transition.15 The separation between the transition being excited and that of the LO-phonon satellite allows for the use of edge pass filters to suppress the elastically scattered light. This method of using the phonon satellite allows for laser linewidth limited resolution, since resonantly exciting the transition is typically the only time that the LO-phonon satellite emission becomes visible.

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high resolution phonon-assisted quasi-resonance fluorescence spectroscopy

High resolution optical spectroscopy methods are demanding in terms of either technology, equipment, complexity, time or a combination of these. Here we demonstrate an optical spectroscopy method that is capable of resolving spectral features beyond that of the spin fine structure and homogeneous linewidth of single quantum dots (QDs) using a standard, easy-to-use spectrometer setup. This method incorporates both laser and photoluminescence spectroscopy, combining the advantage of laser line-width limited resolution with multi-channel photoluminescence detection. Such a scheme allows for considerable improvement of resolution over that of a common single-stage spectrometer. The method uses phonons to assist in the measurement of the photoluminescence of a single quantum dot after resonant excitation of its ground state transition. The phonon&#39;s energy difference allows one to separate and filter out the laser light exciting the quantum dot. An advantageous feature of this method is its straight forward integration into standard spectroscopy setups, which are accessible to most researchers.

The results presented in the figures show the high resolution capabilities of using phonons to assist in the PL measurement. The schematic (Figure 2) shows that, with the exception of the edge pass filters on both excitation and detection, the experimental setup remains a standard spectroscopy setup, with the optional addition of polarization control. Comparison with a single and triple spectrometer (Figure. 3) portrays the phonon-assisted method&#39;s gr...

Watch this Scientific Journal Video about High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy at JoVE.com

High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy

The manuscript describes a method of phonon-assisted quasi-resonant fluorescence spectroscopy that incorporates both laser-limited resolution and photoluminescence (PL) spectroscopy. This method utilizes optical phonons to provide linewidth-limited resolution spectra of atom-like semiconductor structures in the energy domain. The method is also easily realized with a single spectrometer optical spectroscopy setup.

High resolution optical spectroscopy methods are demanding in terms of either technology, equipment, complexity, time or a combination of these. Here we ...

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