Polarization-Dependent Lasing Behavior from Low-Symmetry

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Polarization-Dependent Lasing Behavior from Low-Symmetry Nanocavity Arrays Michael P. Knudson, Ran Li, Danqing Wang, Weijia Wang, Richard D. Schaller, and Teri W. Odom ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.9b01142 • Publication Date (Web): 02 Apr 2019 Downloaded from http://pubs.acs.org on April 3, 2019

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Polarization-Dependent Lasing Behavior from Low-Symmetry Nanocavity Arrays Michael P. Knudson1, Ran Li1, Danqing Wang2, Weijia Wang2, Richard D. Schaller3,4, and Teri W. Odom*,1,2,3 1

Department of Materials Science and Engineering

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Graduate Program in Applied Physics

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Department of Chemistry, Northwestern University, Evanston, Illinois, 60208, USA

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Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL 60439, USA

*Address correspondence to [email protected] Abstract This paper reports how geometric effects in low-symmetry plasmonic nanoparticle arrays can produce polarization-dependent lasing responses. We developed a scalable fabrication procedure to pattern rhombohedral arrays of aluminum anisotropic nanoparticles that support lattice plasmon modes from both first-order and second-order diffraction coupling. We found that nanoparticle shape can be used to engineer the spatial overlap between electromagnetic hot spots of different lattice modes and dye gain to support plasmonic lasing. The lasing behavior revealed that plasmonexciton energy transfer depends on polarization, with stronger coupling and faster dynamics when the transition dipole moments of the excited gain are aligned with the electric field of the plasmon modes. Keywords: lasing, symmetry, lattice plasmons, polarization, aluminum plasmonics, anisotropic nanoparticles

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Geometry is a key factor that determines the properties of photonic nanostructures, including band structure, mode degeneracy, localization of enhanced electric fields, and mode-sensitivity to polarization.1, 2 The breaking or manipulation of symmetry in optical systems has resulted in a range of distinct structures and responses: metal nanoparticles arranged in asymmetric clusters produce chiral interactions with circularly polarized light;3, 4 resonators with broken symmetries enable dark modes to couple to far-field radiation;5,

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and quasicrystals with high orders of

rotational symmetry but no translational symmetry exhibit rotationally invariant band structures. 7-10

Lattice plasmons or surface lattice resonances (collective responses from the localized surface

plasmons (LSPs) of metal nanoparticles coupled to Bragg diffraction modes11-14) can be tuned by changing lattice geometry in situ on stretchable substrates,15, 16 but little work has been performed on low-symmetry lattices. Although arrays of cylindrical nanoparticles have been tested with honeycomb and Lieb crystal structures containing multiple nanoparticles per unit cell, the overall band structures still reflected the underlying hexagonal and square lattices, respectively.17 High quality factors and subwavelength mode confinement of lattice plasmon resonances have enabled their application in enhanced fluorescence18-22 and lasing23-26 by using nanoparticle arrays as optical cavities for gain media. The most common particle lattices are square and hexagonal arrays of cylindrical nanoparticles.2, 15, 27 1D superlattices—2D arrays of nanoparticles patterned into 1D arrays of microscale patterns—show polarization-sensitive responses.28, 29 Moreover, 1D superlattices of gold nanoparticles can switch between either multi-mode or single-mode lasing depending on polarization.25 Finite-lattices of nanoparticles also show lasing from a dark mode by coupling to the edges of the array.26 Although lattice symmetry of plasmonic nanocavities can be directly correlated to optical band structure17 and lasing far-field emission patterns,25 less is known


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about how reducing lattice symmetry can be used to achieve on-demand tuning and switching of lasing emission. Here we show that low-symmetry nanoparticle arrays with anisotropic unit-cell shapes can exhibit polarization-dependent lasing action. Using soft nanolithography, we fabricated cm2-areas of rhombohedral lattices with rhombus-shaped plasmonic nanoparticles. The anisotropic particle structure enabled engineering of the spatial overlap between electromagnetic hot spots of the two lattice plasmon modes and dye gain molecules. We focused on Al nanoparticles to achieve robust lattice plasmon lasing at visible wavelengths. Examination of the lasing dynamics under different pump polarizations revealed that energy transfer between excitons and plasmons was faster when their dipole moments had the same oscillation direction, leading to shorter lasing rise times and decay lifetimes. Switching between the lasing modes of a rhombohedral lattice of Al nanoparticles was performed by changing pump polarization; critically, the regions of population inversion for the two lasing modes were from the same physical hot spot locations. RESULTS AND DISCUSSION Al nanoparticle arrays were fabricated on quartz slides by deposition through sacrificial Au hole-array masks (Figure 1a). Hole-array masks with rhombohedral symmetry were prepared by combining multiple steps of solvent-assisted nanoscale embossing (SANE30), etching, and metal deposition (Figure S1). Briefly, photoresist lines 150-nm wide with a0 = 400 nm were patterned on a Si substrate using SANE with an elastomeric (poly(dimethylsiloxane), PDMS) mold; after Cr deposition and liftoff, an array of Cr lines was produced. This process was then repeated (spincoating photoresist, SANE, Cr deposition, and liftoff) but with the PDMS mold rotated at a selected angle  to create a second set of intersecting Cr lines and form a 2D array of Cr holes. The Cr hole film served as an etch mask for deep reactive-ion etching of pits in the Si substrate.


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Figure 1: Low-symmetry Nanoparticle Arrays. (a) Fabrication scheme using a Au hole array as a physical deposition mask. (b) SEM image of a sample Au hole array patterned with a rhombus-shaped nanoholes arranged in a rhombohedral lattice. (c) SEM image of a rhombohedral Al nanoparticle array showing the lattice vectors. (d) The reciprocal space for a rhombohedral lattice with first order modes shown in blue and second order modes in green. (e) Transmission spectra showing two lattice modes. Au deposition followed by etching of the Cr film resulted in free-standing hole arrays as masks for nanoparticle formation (Figure 1b). This process generated rhombohedral lattices of rhombusshaped nanoparticles 80 nm wide by 130 nm long (Figure 1c) and 100 nm tall (Figure S2). We achieved an accuracy of ±3° in  and focused on angles between 60° - 70° ( = 62°, 67°) to optimize the position of the Bragg diffraction modes relative to the LSP resonance along the short axis of the nanoparticles. The long-axis LSP wavelength was too red to couple with the Bragg modes of this array. We have demonstrated that gratings with rhombohedral symmetry exhibit broadband plasmonic resonances that depend on lattice angle  defined by the basis vectors.31 Rhombohedral lattices are defined by two real-space basis vectors a1 and a2 of equal length (𝑎0 / sin 𝜃) forming a lattice angle  (Figure 1c, overlay) with reciprocal-space vectors: 𝒌1 = 〈−cos(𝜃/2) , sin(𝜃/2)〉


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𝒌2 = 〈cos(𝜃/2) , sin(𝜃/2)〉

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(1)

The reciprocal lattice is indexed using (i,j) to represent a combination of basis vectors ik1 + jk2 (Figure 1d). Each point in reciprocal space represents a wavevector contribution for a Bragg mode with wavelength 𝜆 = 𝑛𝑎0⁄|𝒌𝑖𝑗 | at normal angle, where n is refractive index, and a0 is periodicity. Al nanoparticle arrays were covered with dimethyl sulfoxide (DMSO) (n = 1.47) to match the index of the quartz substrate (n = 1.45). The zero-order transmission spectrum normal to the substrate for the  = 67° lattice showed two lattice plasmon modes: 𝜆1 = 513 nm and 𝜆2 = 570 nm under TM polarization, which was along the short axis of the nanoparticles (𝜑 = 0°) (Figure 1e). Because lattice plasmon modes at green wavelengths are not possible from Au or Ag nanoparticle arrays because of the interband transition wavelengths of the metals,15 we used Al nanoparticles to access these modes. The  = 62° lattice showed similar behavior for 𝜆2 = 570 nm but a longer wavelength for 𝜆1 = 553 nm (Figures S3a-c). Transmission spectra at different incidence angles compiled into dispersion diagrams revealed why one resonance was at the same wavelength (𝜆2) while the other changed depending on lattice angle (𝜆1) (Figure S3d-e). The lattice plasmon modes closely followed the dispersive Bragg modes from analytical calculations and formed two band edge states with near-zero group velocity vg = d𝜔/dk at k = 0. The band edge at 𝜆2 based on the coupling of first-order Bragg modes to the nanoparticle LSP has been the focus of most previous work.13, 15, 23, 24, 26 Here, the band edge at 𝜆1 results from interactions between the particle LSP and second-order Bragg modes and emerges as the lattice symmetry is reduced. Second-order Bragg coupling with plasmon modes has been observed with waveguides;32 for the lattice plasmon mode at 𝜆1, the index around the aluminum nanoparticle lattice is uniform.


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Simulated transmission spectra of Al nanoparticles arrays (n = 1.42) using finite-difference time-domain (FDTD) methods indicated that calculated lattice modes were in excellent agreement with measured data (Figure 1e). Since previous work mostly considered circular nanoparticles, we used FDTD simulations to analyze how the anisotropic nanoparticle shape affected the location of hot spots for the same rhombohedral lattice geometry. Phase maps at the lattice plasmon wavelengths showed characteristic standing wave behavior with horizontal polarization (𝜑1 = 0°) for the λ1 mode and diagonal polarization (𝜑2 = 56.5°, along a1) for the λ2 mode (Figures 2a-d). These directions were defined by the (1,1) and (1,0) Bragg modes of the rhombohedral lattice. Near-field intensity maps revealed that the locations of the plasmonic hot spots depended on nanoparticle shape. For rhombus-shaped nanoparticles, both the λ1 mode and λ2 mode showed hot spots concentrated at the nanoparticle corners along the short axis (Figure 2e and 2g). In contrast, for circular particles, the hot spots aligned with mode oscillation because of the isotropic particle shape (Figures 2f and 2h, Figure S4). Therefore, we found that array geometry can engineer specific regions of electric field enhancement.

Figure 2: Near-field maps of rhombus-shaped and circular nanoparticles. (a-b) Phase for 𝜆 1 showing standing waves for the (1,1) mode with rhombohedral and circular particles, respectively. (c-d) Phase for 𝜆2 showing standing waves for the (1,0) mode. (e-f) Electric field intensity for 𝜆1. (g-h) Electric field intensity for 𝜆2.


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We integrated Al rhombohedral lattices with a green laser dye (C-481, whose broad photoluminescence spectrally overlaps both lattice modes) to create plasmon laser devices (Figure 3a). The dye (20 mM concentration) was excited with a 400-nm, pulsed pump source (35 fs, 1 kHz) at normal incidence, and emission was collected normal to the sample. A depolarizer removed the source polarization. A dichroic mirror reflected the 400-nm pump beam toward the sample for normal incidence excitation, and sample emission with wavelengths > 500 nm was transmitted through the dichroic mirror for collection by a spectrometer. Spectrally narrow lasing peaks (FWHM < 1.5 nm) appeared at both 𝜆1 and 𝜆2 lattice plasmon wavelengths (Figure 3b). Differences in relative emission intensity of the two laser modes can be attributed to optical mode quality and spectral overlap of each mode with the dye photoluminescence. Lasing intensities rose

Figure 3: Lasing measurements of rhombohedral array. (a) Scheme of experimental setup for lasing measurements with pumping and collecting emission at normal incident angle. (b) Lasing spectrum for 67° lattice angle with overlay of dye emission. (c) Light-light curve showing evolution of lasing emission intensity for increasing pump intensity with an inset showing a zoomed-in view of the lasing threshold.


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sharply above threshold due to the high concentration of gain (5-s pause between measurements), and the background emission was several orders of magnitude lower. Emission intensity showed thresholds between 0.7-0.8 mJ/cm2 for both lasing modes (Figure 3c). Above pump intensities > 1.5 mJ/cm2, lasing emission plateaued and remained stable up to the maximum investigated intensity (3.3 mJ/cm2). Far-field beam profile measurements revealed that the emission was a welldefined beam at surface normal with divergence angle < 1.5° (Figure S5). Previous studies of lattice plasmon lasers based on square arrays of isotropic nanoparticles showed similar divergence angles and elongated beam profiles caused by ASE at off-normal angles.23, 24 Not surprisingly,  = 62° lattices exhibited lasing action with linewidths, threshold behavior, and beam profiles similar to  = 67° lattices but with more closely spaced emission wavelengths (Figure S6). The slightly lower thresholds (0.6-0.7 mJ/cm2) were likely due to differences in mode quality, which is sensitive to nanoparticle width. To determine spatial regions contributing to population inversion, we examined the near-field intensity maps in FDTD simulations. Changing in-plane pump polarization resulted in switching between lasing modes (Figure 4a). 𝜆1 lasing dominated near horizontal polarization (𝜑1 = 0°) and 𝜆2 lasing near the diagonal polarization (𝜑2 = 56.5°, along a1), which corresponded to the standing wave behavior (Figures 2a, 2c). Lasing emission from both modes was supported at intermediate polarizations (𝜑 = 40° as one example). Simulations of cylindrical nanoparticles in a rhombohedral lattice showed similar switchable lasing spectra (Figure S7). Calculated spatial maps indicate that 1

maximum regions of the stimulated emission rate (ℏ𝑤 𝑬𝑑𝑷 ) for both lasing modes were at the edges 𝑑𝑡 of the rhombohedral nanoparticles along the short axis (Figures 4b-d); these areas overlapped with the enhanced local fields of lattice plasmon modes (Figures 2e, g). Importantly, although the two lattice plasmon cavity modes overlap spatially, they couple to different populations of dye


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Figure 4: Simulated emission profiles at the onset of lasing. (a) Simulated lasing spectra of a 67° array for different in-plane polarization angles 𝜑. (b-d) Associated stimulated emission mappings show lattice plasmon lasing hot spots at the nanoparticle corners along the short axis. (e-f) Spontaneous emission hot spots with lower intensity change location based on pump polarization. molecules within the shared hot spots according to their transition dipole moments. Therefore, lasing from two modes is possible by the random dipole orientations of dye molecules in solution. Maps of spontaneous emission rate (N2/21) for rhombohedral arrays were sensitive to polarization and showed intensities 14 orders of magnitude weaker than stimulated emission (Figures 4e-g). Emission maps showing the entire unit cell used in calculations confirmed that both stimulated emission and spontaneous emission were strongest close to the nanoparticles (Figure S8). The Purcell effect depends on mode volume, quality factor, wavelength, and polarization and can increase the emission rates of emitters within optical cavities.33 Hence, we expect lasing should exhibit accelerated emission lifetimes depending on the alignment between pump polarization and lattice plasmon mode oscillation direction. We found that pump polarization influenced spectral output and lasing dynamics of plasmon-exciton coupling. We characterized simultaneously the temporal and spectral output of lasing emission from rhombohedral lattice plasmon lasers (Figure


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5a and Figure S9). The horizontal white line at time t = 0 corresponds to the pump laser pulses, and plasmon lasing signals followed the pump by 40-100 ps. Emission maps exhibited spectrally narrow signals (x-axis) with a sharp rise in intensity followed by gradual decay in time (y-axis). Lasing emission from the 𝜆1 and 𝜆2 modes appeared when the pump polarization aligned with their respective lattice mode oscillation directions (𝜑1 = 0° and 𝜑2 = 56.5°), similar to switchable lasing in other nanolasers with liquid gain.25, 34 At pump polarization of 90°, only spontaneous emission was observed, and there was no lasing from either lattice cavity mode. We binned emission data

Figure 5: Polarization dependent lasing dynamics. (a) Temporally and spectrally resolved streak camera images showing lasing output as a function of time and wavelength for different in-plane pump polarizations 𝜑 in the case of a 67° array. Simulated spectra (b) and emission dynamics (c). Faster dynamics are seen at polarization angles close to the 𝜆1 mode polarization at 𝜑1 = 0° and the 𝜆2 mode polarization at 𝜑2 = 56.5°.


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according to wavelength to examine trends in dynamics (Figure S10). The rise time represents the period of excited population accumulation leading to the onset of lasing and can be characterized by the delay time between pump pulse (t = 0) and lasing emission. We observed shorter 𝜆1 rise times for polarization close to 𝜑1 = 0° for both  = 67° lattices (Figure S10a) and  = 62° lattices (Figure S10b). Similarly, the 𝜆2 rise time was shorter for pump polarization close to the second lattice mode oscillation direction (𝜑2 = 56.5° or 59°). Changes in photon dynamics were also observed in the decay lifetime. To extract stimulated emission lifetimes, we fit a single-exponential decay function (I = A + I0 𝑒

−t⁄ τ,

where τ is decay

lifetime) to the emission.25 We could not measure spontaneous emission alongside stimulated emission because the spontaneous emission intensity was several orders of magnitude weaker. We discovered that the decay lifetime at λ1 was shorter for polarizations close to the first lattice mode oscillation direction (𝜑1 = 0°) for both lattice angles tested. Lifetimes for lasing at λ2 were shorter near the second lattice mode oscillation direction (𝜑2 = 56.5° or 59°). The intrinsic emission decay lifetime (586 ± 18 ps) for the dye solution without a nanoparticle array was more than an order of magnitude longer than the lasing lifetimes (7-30 ps) (Figure S11). Dyes with transition dipoles aligned to lattice plasmon oscillations produced faster plasmon-exciton energy transfer and led to shorter rise time and faster lifetime at certain pump polarizations. We performed FDTD simulations of Al nanoparticle arrays in a 4-level gain model25 based on the C-481 dye to obtain further insight into the measured polarization-dependent lasing dynamics. Although the simulated lasing emission under different pump polarization 𝜑 (Figure 5b) was in agreement with experiment, the spectral linewidths were broader than those measured because the rate equations lacked dephasing considerations,35 and the simulation times were limited.25 Pump polarizations with 𝜑 = 0° - 50° resulted in lasing at 𝜆 1, and polarizations with 𝜑 = 40° - 90°


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produced lasing at 𝜆2. The emission dynamics (monitored as electric field intensity) showed two sets of decay peaks (Figure 5c). The earlier set of peaks from 0.8-2 ps corresponded to lasing at 𝜆1 while the second set of peaks from 1.5-3 ps were from lasing at 𝜆2. Lasing at the two modes showed faster rise times and shorter decay lifetimes when the pump polarizations were closer to the corresponding lattice mode oscillation direction (𝜑1 = 0°, 𝜑2 = 56.5°). This simulated behavior agrees qualitatively with experimental trends and supports that faster plasmon-exciton energy transfer dynamics occur when the transition dipoles of the gain are aligned with the electric field of the plasmon oscillations. CONCLUSIONS In summary, we found that nanoparticle shape, lattice symmetry, and emitter transition dipole orientation have a direct influence on the electromagnetic hot spots responsible for plasmon lasing and associated dynamics. Rhombic nanoparticles can support hot spots in the same locations but from different lattice modes; hence, dye molecules with random dipole orientations localized to these regions can couple to different modes and result in lasing at different wavelengths depending on polarization. Notably, plasmon-exciton coupling and energy transfer dynamics depend on the orientation of the transition dipole moments in the gain relative to the electric field of the plasmon mode. These results offer a strategy to integrate open optical cavities with low-dimensional semiconductors that exhibit anisotropic emission.36, 37 Moreover, understanding the correlation between cavity modes and emission dynamics will enable selective modulation speeds for applications in optical sensing and communications.38, 39


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METHODS Fabrication of Au Hole Array Masks: Si wafers were treated with MicroChem MCC Primer 80/20. Shipley 1805 photoresist was diluted with propylene glycol monomethyl ether acetate (PGMEA), spun on the wafers to thickness of 90 nm, and baked at 115 C for 2 minutes. PDMS stamps patterned with 400-nm periodic lines were used to perform solvent-assisted nanoscale embossing (SANE) with dimethylformamide (DMF) as the solvent.30 Residual resist was removed with a brief oxygen plasma treatment. A thin (7-nm) Cr film was deposited by thermal evaporation, followed by resist liftoff using MicroChem Remover 1165. The previous steps were repeated a second time with the lines rotated at the chosen lattice angle to form a Cr hole array. Si masked by Cr was etched to form pits by deep reactive ion etching (DRIE) using a co-flow of SF6 and C4F8 process gases.40, 41 A thick (120-nm) layer of Au was deposited by thermal evaporation, producing a gold hole array. Wet etching the Cr adhesion layer (Transene Cr Etchant) released the Au hole array from the silicon, so it could float on water for transfer to a quartz substrate. Al nanoparticles 100-nm tall were deposited by e-beam evaporation using the Au hole array as a physical deposition mask, after which the mask was removed using adhesive tape. Finite-Difference Time-Domain Simulations: Simulations were performed using commercial software (Lumerical). Simulations used a background index of n = 1.42, and a 4-nm mesh was applied to the rhombohedral Al nanoparticles (Palik). The rhombohedral lattice geometry was defined using 2 or 4 nanoparticles per simulation area and applying periodic (nonsymmetric) x- and y-boundary conditions. Perfectly matched layers were applied at the z-boundary conditions. Transmission simulations used a broadband light source, while lasing simulations were pumped using 400-nm wavelength light. For lasing simulations, nanoparticles were embedded in a layer of gain material modeled as a 4-level system for the laser dye with an absorption peak near 400 nm, broad emission centered at 520 nm, and concentration of 20 mM. Transition lifetimes were set to 𝜏30 = 𝜏21 = 1 ns and 𝜏32 = 𝜏10 = 1 0 fs, which provide representative trends in 1

dynamics.23 Stimulated (ℏ𝑤 𝑬𝑑𝑷 ) and spontaneous emission rates (N2/21) were mapped using an 𝑑𝑡 array of point monitors (2436) in the plane of the nanoparticles to track the energy level populations for the gain medium. The snapshots of emission rates were taken at the onset of lasing. Lasing Measurements: A drop of 20 mM solution of C-481 dye dissolved in DMSO was placed on each nanoparticle array and capped with a cover slip. We found that 20 mM dye


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concentration produced lasing in our system, but lower dye concentrations we tested up to 10 mM did not provide sufficient gain to overcome cavity loss. The completed samples were pumped at normal incidence using 35-fs, 400-nm laser pulses with a repetition rate of 1 kHz, beam diameter of 152 microns, and controlled pulse energies up to 3.3 mJ/cm2 using a variable neutral density filter. The polarized pump beam was either passed through a depolarizer to produce unpolarized light (Figure 3 experiments) or through a half-wave plate to rotate the polarization angle (Figure 5 experiments). Pulsed laser emission was collected normal to the sample with pump signal removed using a dichroic mirror and long-pass filters. Far-field emission with a free space distance from the sample of at least several cm was examined using either a spectrometer and CCD, beam profiler, or streak camera. Beam Profile Measurements: A two-dimensional charge coupled device (CCD) array was positioned directly behind the nanolaser to collect the sample-normal emission. A combination of two long-pass filters (560 nm and 570 nm) was used to isolate the longer-wavelength mode at 570 nm, and they were replaced with a band pass filter (515 nm or 550 nm, 10 nm pass band) to isolate the shorter-wavelength mode at 513 nm or 553 nm. The effectiveness of these filters was verified based on the laser spectral profiles before implementing the filters with the beam profiler. The intensity distribution above lasing threshold was mapped spatially for the beam profile crosssection in the x-y plane. The distance z from the nanolaser to the beam profiler CCD was measured and used to convert from pixels to divergence angle. Time-Resolved Photoluminescence: Sample emission following pulsed excitation was coupled into a spectrograph and streak camera that was synchronized to the 1 kHz repetition rate of the pump laser so repeated nanolaser pulses were synchronized on the detector. Integration times of 0.5 seconds allowed averaging over several nanolaser pulses. Streak camera data was binned by wavelength with an 8-nm bin width around each laser mode. Each emission curve was fit to a single exponential decay using time points following peak emission intensity. ACKNOWLEDGEMENTS This work was supported by the Vannevar Bush Faculty Fellowship from the DOD under Grant No. N00014-17-1-3023. Research for this paper was conducted with Government support under contract FA9550-11-C-0028 and awarded by the Department of Defense, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship


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(M.P.K.), 32 CFR 168a. This work made use of the EPIC, Keck-II, and SPID facilities of Northwestern University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. This work utilized the Northwestern University Micro/Nano Fabrication Facility (NUFAB) and the Materials Processing and Microfabrication Facility (NUFAB-Cook). This research was supported in part through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University, which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Supporting Information Available: Scheme for nanoparticle array fabrication; AFM images of nanoparticle heights; optical transmission properties of anisotropic nanoparticle arrays; optical transmission properties of circular nanoparticle arrays; beam profile measurements for lasing; lasing spectrum and light-light curve for a 62° lattice angle; temporally and spectrally resolved emission maps for a 62° lattice angle; laser emission decay curves for characterizing lifetimes; C481 dye emission decay curve for measuring intrinsic lifetime.


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Polarization-Dependent Lasing Behavior from Low-Symmetry

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