Merge remote-tracking branch 'origin/HEAD'

content/publication/azeem-dielectric-2021/cite.bib

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+@article{azeem_dielectric_2021,
+ abstract = {Small perturbations in the dielectric environment around resonant dielectric structures usually lead to a frequency shift of the resonator modes directly proportional to the polarizability of the perturbation. Here, we report experimental observations of strong frequency shifts that can oppose and even exceed the contribution of the perturbations’ polarizability. We show in particular how the mode frequencies of a lithium niobate whispering-gallery-mode resonator are shifted by planar substrates—of refractive indices ranging from 1.50 to 4.22—contacting the resonator rim. Both blue- and redshifts are observed, as well as an increase in mode linewidth, when substrates are moved into the evanescent field of the whispering gallery mode. We compare the experimental results to a theoretical model by Foreman et al. [J. Opt. Soc. Am. B33, 2177 (2016)JOBPDE0740-322410.1364/JOSAB.33.002177] and provide an additional intuitive explanation based on the Goos–Hänchen shift for the optical domain, with applications to dielectric structures ranging from meta-surfaces to photonic crystal cavities.},
+ author = {Azeem, Farhan and Trainor, Luke S. and Devane, Patrick A. and Norman, Daniel S. and Rueda, Alfredo and Lambert, Nicholas J. and Kumari, Madhuri and Foreman, Matthew R. and Schwefel, Harald G. L.},
+ doi = {10.1364/OL.420791},
+ issn = {1539-4794},
+ journal = {Optics Letters},
+ keywords = {Lithium niobate, Refractive index, Parametric down conversion, Tunable diode lasers, Photonic crystal cavities, Quantum optics},
+ month = {May},
+ note = {citations $≥$ 3 },
+ number = {10},
+ pages = {2477--2480},
+ shorttitle = {Dielectric perturbations},
+ title = {Dielectric perturbations: anomalous resonance frequency shifts in optical resonators},
+ url = {https://www.osapublishing.org/ol/abstract.cfm?uri=ol-46-10-2477},
+ urldate = {2021-05-15},
+ volume = {46},
+ year = {2021}
+}

content/publication/azeem-dielectric-2021/index.md

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+---
+title: 'Dielectric perturbations: anomalous resonance frequency shifts in optical
+  resonators'
+authors:
+- Farhan Azeem
+- Luke S. Trainor
+- Patrick A. Devane
+- Daniel S. Norman
+- Alfredo Rueda
+- Nicholas J. Lambert
+- Madhuri Kumari
+- Matthew R. Foreman
+- Harald G. L. Schwefel
+date: '2021-05-01'
+publishDate: '2024-06-19T11:08:09.102911Z'
+publication_types:
+- article-journal
+publication: '*Optics Letters*'
+doi: 10.1364/OL.420791
+abstract: Small perturbations in the dielectric environment around resonant dielectric
+  structures usually lead to a frequency shift of the resonator modes directly proportional
+  to the polarizability of the perturbation. Here, we report experimental observations
+  of strong frequency shifts that can oppose and even exceed the contribution of the
+  perturbations’ polarizability. We show in particular how the mode frequencies of
+  a lithium niobate whispering-gallery-mode resonator are shifted by planar substrates—of
+  refractive indices ranging from 1.50 to 4.22—contacting the resonator rim. Both
+  blue- and redshifts are observed, as well as an increase in mode linewidth, when
+  substrates are moved into the evanescent field of the whispering gallery mode. We
+  compare the experimental results to a theoretical model by Foreman et al. [J. Opt.
+  Soc. Am. B33, 2177 (2016)JOBPDE0740-322410.1364/JOSAB.33.002177] and provide an
+  additional intuitive explanation based on the Goos–Hänchen shift for the optical
+  domain, with applications to dielectric structures ranging from meta-surfaces to
+  photonic crystal cavities.
+tags:
+- Lithium niobate
+- Refractive index
+- Parametric down conversion
+- Tunable diode lasers
+- Photonic crystal cavities
+- Quantum optics
+links:
+- name: URL
+  url: https://www.osapublishing.org/ol/abstract.cfm?uri=ol-46-10-2477
+---

content/publication/azeem-ultra-low-2022/cite.bib

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+@article{azeem_ultra-low_2022,
+ abstract = {Titanium doped sapphire (Ti:sapphire) is a laser gain material with broad gain bandwidth benefiting from the material stability of sapphire. These favorable characteristics of Ti:sapphire have given rise to femtosecond lasers and optical frequency combs. Shaping a single Ti:sapphire crystal into a millimeter sized high quality (Q) whispering gallery mode resonator (Q ≈ 108) reduces the lasing threshold to 14.2 mW and increases the laser slope efficiency to 34%. The observed lasing can be both multi-mode and single-mode. This is the first demonstration of a Ti:sapphire whispering-gallery laser. Furthermore, a novel method of evaluating the gain in Ti:sapphire in the near infrared region is demonstrated by introducing a probe laser with a central wavelength of 795 nm. This method results in decreasing linewidth of the modes excited with the probe laser, consequently increasing their Q. These findings open avenues for the usage of whispering gallery mode resonators as cavities for the implementation of compact Ti:sapphire lasers. Moreover, Ti:sapphire whispering-gallery laser can also be utilized as an amplifier inside its gain bandwidth by implementing a pump–probe configuration.},
+ author = {Azeem, Farhan and Trainor, Luke S. and Gao, Ang and Isarov, Maya and Strekalov, Dmitry V. and Schwefel, Harald G. L.},
+ doi = {10.1002/adom.202102137},
+ file = {Full Text PDF:/Users/harry/Zotero/storage/USQ4ERNI/Azeem et al. - 2022 - Ultra-Low Threshold Titanium-Doped Sapphire Whispe.pdf:application/pdf;Snapshot:/Users/harry/Zotero/storage/NBVKGQPI/adom.html:text/html},
+ issn = {2195-1071},
+ journal = {Advanced Optical Materials},
+ keywords = {Ti:sapphire, whispering-gallery laser, whispering-gallery modes},
+ note = {Cover Article, citations $≥$ 4},
+ number = {8},
+ pages = {2102137},
+ title = {Ultra-Low Threshold Titanium-Doped Sapphire Whispering-Gallery Laser},
+ url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202102137},
+ urldate = {2022-05-04},
+ volume = {10},
+ year = {2022}
+}

content/publication/azeem-ultra-low-2022/index.md

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+---
+title: Ultra-Low Threshold Titanium-Doped Sapphire Whispering-Gallery Laser
+authors:
+- Farhan Azeem
+- Luke S. Trainor
+- Ang Gao
+- Maya Isarov
+- Dmitry V. Strekalov
+- Harald G. L. Schwefel
+date: '2022-01-01'
+publishDate: '2024-06-19T11:08:09.138605Z'
+publication_types:
+- article-journal
+publication: '*Advanced Optical Materials*'
+doi: 10.1002/adom.202102137
+abstract: Titanium doped sapphire (Ti:sapphire) is a laser gain material with broad
+  gain bandwidth benefiting from the material stability of sapphire. These favorable
+  characteristics of Ti:sapphire have given rise to femtosecond lasers and optical
+  frequency combs. Shaping a single Ti:sapphire crystal into a millimeter sized high
+  quality (Q) whispering gallery mode resonator (Q ≈ 108) reduces the lasing threshold
+  to 14.2 mW and increases the laser slope efficiency to 34%. The observed lasing
+  can be both multi-mode and single-mode. This is the first demonstration of a Ti:sapphire
+  whispering-gallery laser. Furthermore, a novel method of evaluating the gain in
+  Ti:sapphire in the near infrared region is demonstrated by introducing a probe laser
+  with a central wavelength of 795 nm. This method results in decreasing linewidth
+  of the modes excited with the probe laser, consequently increasing their Q. These
+  findings open avenues for the usage of whispering gallery mode resonators as cavities
+  for the implementation of compact Ti:sapphire lasers. Moreover, Ti:sapphire whispering-gallery
+  laser can also be utilized as an amplifier inside its gain bandwidth by implementing
+  a pump–probe configuration.
+tags:
+- Ti:sapphire
+- whispering-gallery laser
+- whispering-gallery modes
+links:
+- name: URL
+  url: https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202102137
+---

content/publication/botello-sensitivity-2018/cite.bib

@@ -0,0 +1,19 @@
+@article{botello_sensitivity_2018,
+ abstract = {Conventional ultra-high sensitivity detectors in the millimeter-wave range are usually cooled as their own thermal noise at room temperature would mask the weak received radiation. The need for cryogenic systems increases the cost and complexity of the instruments, hindering the development of, among others, airborne and space applications. In this work, the nonlinear parametric upconversion of millimeter-wave radiation to the optical domain inside high-quality (Q) lithium niobate whispering-gallery mode (WGM) resonators is proposed for ultra-low noise detection. We experimentally demonstrate coherent upconversion of millimeter-wave signals to a 1550 nm telecom carrier, with a photon conversion efficiency surpassing the state-of-the-art by 2 orders of magnitude. Moreover, a theoretical model shows that the thermal equilibrium of counterpropagating WGMs is broken by overcoupling the millimeter-wave WGM, effectively cooling the upconverted mode and allowing ultra-low noise detection. By theoretically estimating the sensitivity of a correlation radiometer based on the presented scheme, it is found that room-temperature radiometers with better sensitivity than state-of-the-art high-electron-mobility transistor (HEMT)-based radiometers can be designed. This detection paradigm can be used to develop room-temperature instrumentation for radio astronomy, earth observation, planetary missions, and imaging systems.},
+ author = {Botello, Gabriel Santamaría and Sedlmeir, Florian and Rueda, Alfredo and Abdalmalak, Kerlos Atia and Brown, Elliott R. and Leuchs, Gerd and Preu, Sascha and Segovia-Vargas, Daniel and Strekalov, Dmitry V. and Muñoz, Luis Enrique García and Schwefel, Harald G. L.},
+ copyright = {© 2018 Optical Society of America},
+ doi = {10.1364/OPTICA.5.001210},
+ file = {Full Text PDF:/Users/harry/Zotero/storage/RRRPTPZU/Botello et al. - 2018 - Sensitivity limits of millimeter-wave photonic rad.pdf:application/pdf;Snapshot:/Users/harry/Zotero/storage/FN5EWMLM/abstract.html:text/html},
+ issn = {2334-2536},
+ journal = {Optica},
+ keywords = {Sum frequency generation, Q factor, Power spectral density, Amplified spontaneous emission, Coupled mode theory, Nonlinear parametric processes},
+ month = {October},
+ note = { citations $≥$ 27},
+ number = {10},
+ pages = {1210--1219},
+ title = {Sensitivity limits of millimeter-wave photonic radiometers based on efficient electro-optic upconverters},
+ url = {https://www.osapublishing.org/optica/abstract.cfm?uri=optica-5-10-1210},
+ urldate = {2018-09-29},
+ volume = {5},
+ year = {2018}
+}

content/publication/botello-sensitivity-2018/index.md

@@ -0,0 +1,49 @@
+---
+title: Sensitivity limits of millimeter-wave photonic radiometers based on efficient
+  electro-optic upconverters
+authors:
+- Gabriel Santamaría Botello
+- Florian Sedlmeir
+- Alfredo Rueda
+- Kerlos Atia Abdalmalak
+- Elliott R. Brown
+- Gerd Leuchs
+- Sascha Preu
+- Daniel Segovia-Vargas
+- Dmitry V. Strekalov
+- Luis Enrique García Muñoz
+- Harald G. L. Schwefel
+date: '2018-10-01'
+publishDate: '2024-06-19T11:08:09.022928Z'
+publication_types:
+- article-journal
+publication: '*Optica*'
+doi: 10.1364/OPTICA.5.001210
+abstract: Conventional ultra-high sensitivity detectors in the millimeter-wave range
+  are usually cooled as their own thermal noise at room temperature would mask the
+  weak received radiation. The need for cryogenic systems increases the cost and complexity
+  of the instruments, hindering the development of, among others, airborne and space
+  applications. In this work, the nonlinear parametric upconversion of millimeter-wave
+  radiation to the optical domain inside high-quality (Q) lithium niobate whispering-gallery
+  mode (WGM) resonators is proposed for ultra-low noise detection. We experimentally
+  demonstrate coherent upconversion of millimeter-wave signals to a 1550 nm
+  telecom carrier, with a photon conversion efficiency surpassing the state-of-the-art
+  by 2 orders of magnitude. Moreover, a theoretical model shows that the thermal equilibrium
+  of counterpropagating WGMs is broken by overcoupling the millimeter-wave WGM, effectively
+  cooling the upconverted mode and allowing ultra-low noise detection. By theoretically
+  estimating the sensitivity of a correlation radiometer based on the presented scheme,
+  it is found that room-temperature radiometers with better sensitivity than state-of-the-art
+  high-electron-mobility transistor (HEMT)-based radiometers can be designed. This
+  detection paradigm can be used to develop room-temperature instrumentation for radio
+  astronomy, earth observation, planetary missions, and imaging systems.
+tags:
+- Sum frequency generation
+- Q factor
+- Power spectral density
+- Amplified spontaneous emission
+- Coupled mode theory
+- Nonlinear parametric processes
+links:
+- name: URL
+  url: https://www.osapublishing.org/optica/abstract.cfm?uri=optica-5-10-1210
+---

content/publication/breunig-whispering-2013/cite.bib

@@ -0,0 +1,17 @@
+@article{breunig_whispering_2013,
+ abstract = {Optical whispering gallery modes (WGMs) of mm-sized axisymmetric resonators are well localized at the equator. Employing this distinctive feature, we obtain simple analytical relations for the frequencies and eigenfunctions of WGMs which include the major radius of the resonator and the curvature radius of the rim. Being compared with results of finite-element simulations, these relations show a high accuracy and practicability. High-precision free-spectral-range measurements with a millimeter-sized disc resonator made of MgF2 allow us to identify the WGMs and confirm the applicability of our analytical description.},
+ author = {Breunig, Ingo and Sturman, Boris and Sedlmeir, Florian and Schwefel, Harald G. L. and Buse, Karsten},
+ doi = {10.1364/OE.21.030683},
+ journal = {Optics Express},
+ keywords = {Optical resonators, Resonators},
+ month = {December},
+ note = { citations $≥$ 72},
+ number = {25},
+ pages = {30683--30692},
+ shorttitle = {Whispering gallery modes at the rim of an axisymmetric optical resonator},
+ title = {Whispering gallery modes at the rim of an axisymmetric optical resonator: Analytical versus numerical description and comparison with experiment},
+ url = {http://www.opticsexpress.org/abstract.cfm?URI=oe-21-25-30683},
+ urldate = {2013-12-05},
+ volume = {21},
+ year = {2013}
+}

content/publication/breunig-whispering-2013/index.md

@@ -0,0 +1,30 @@
+---
+title: 'Whispering gallery modes at the rim of an axisymmetric optical resonator:
+  Analytical versus numerical description and comparison with experiment'
+authors:
+- Ingo Breunig
+- Boris Sturman
+- Florian Sedlmeir
+- Harald G. L. Schwefel
+- Karsten Buse
+date: '2013-12-01'
+publishDate: '2024-06-19T11:08:08.834578Z'
+publication_types:
+- article-journal
+publication: '*Optics Express*'
+doi: 10.1364/OE.21.030683
+abstract: Optical whispering gallery modes (WGMs) of mm-sized axisymmetric resonators
+  are well localized at the equator. Employing this distinctive feature, we obtain
+  simple analytical relations for the frequencies and eigenfunctions of WGMs which
+  include the major radius of the resonator and the curvature radius of the rim. Being
+  compared with results of finite-element simulations, these relations show a high
+  accuracy and practicability. High-precision free-spectral-range measurements with
+  a millimeter-sized disc resonator made of MgF2 allow us to identify the WGMs and
+  confirm the applicability of our analytical description.
+tags:
+- Optical resonators
+- Resonators
+links:
+- name: URL
+  url: http://www.opticsexpress.org/abstract.cfm?URI=oe-21-25-30683
+---

content/publication/carmon-syosv-08/cite.bib

@@ -0,0 +1,24 @@
+@article{CarmonSYOSV08,
+ abstract = {We study level crossing in the optical
+whispering-gallery (WG) modes by using toroidal microcavities.
+Experimentally, we image the stationary envelope patterns of the
+composite optical modes that arise when WG modes of different
+wavelengths coincide in frequency. Numerically, we calculate
+crossings of levels that correspond with the observed degenerate
+modes, where our method takes into account the not perfectly
+transverse nature of their field polarizations. In addition, we
+analyze anticrossing with a large avoidance gap between modes of
+the same azimuthal number.
+},
+ author = {Tal Carmon and Harald G. L. Schwefel and Lan Yang and
+Mark Oxborrow and A. Douglas Stone and Kerry J. Vahala},
+ doi = {10.1103/PhysRevLett.100.103905},
+ journal = {Physical Review Letters},
+ note = { citations $≥$ 98},
+ pages = {103905},
+ title = {Static envelope patterns in composite resonances
+generated by level crossing in optical toroidal microcavities},
+ url = {http://link.aps.org/abstract/PRL/v100/e103905 },
+ volume = {100},
+ year = {2008}
+}

content/publication/carmon-syosv-08/index.md

@@ -0,0 +1,27 @@
+---
+title: Static envelope patterns in composite resonances generated by level crossing
+  in optical toroidal microcavities
+authors:
+- Tal Carmon
+- Harald G. L. Schwefel
+- Lan Yang
+- Mark Oxborrow
+- A. Douglas Stone
+- Kerry J. Vahala
+date: '2008-01-01'
+publishDate: '2024-06-19T11:08:08.748797Z'
+publication_types:
+- article-journal
+publication: '*Physical Review Letters*'
+doi: 10.1103/PhysRevLett.100.103905
+abstract: 'We study level crossing in the optical whispering-gallery (WG) modes by
+  using toroidal microcavities. Experimentally, we image the stationary envelope patterns
+  of the composite optical modes that arise when WG modes of different wavelengths
+  coincide in frequency. Numerically, we calculate crossings of levels that correspond
+  with the observed degenerate modes, where our method takes into account the not
+  perfectly transverse nature of their field polarizations. In addition, we analyze
+  anticrossing with a large avoidance gap between modes of the same azimuthal number. '
+links:
+- name: URL
+  url: 'http://link.aps.org/abstract/PRL/v100/e103905 '
+---

content/publication/christensen-distance-2022/cite.bib

@@ -0,0 +1,20 @@
+@article{christensen_distance_2022,
+ abstract = {In this work, we analyze the first whispering gallery mode resonator (WGMR) made from monocrystalline yttrium lithium fluoride (YLF). The disc-shaped resonator is fabricated using single-point diamond turning and exhibits a high intrinsic quality factor (Q) of 8×108. Moreover, we employ a novel, to the best of our knowledge, method based on microscopic imaging of Newton’s rings through the back of a trapezoidal prism. This method can be used to evanescently couple light into a WGMR and monitor the separation between the cavity and the coupling prism. Accurately calibrating the distance between a coupling prism and a WGMR is desirable as it can be used to improve experimental control and conditions, i.e., accurate coupler gap calibration can aid in tuning into desired coupling regimes and can be used to avoid potential damage caused by collisions between the coupling prism and the WGMR. Here, we use two different trapezoidal prisms together with the high-Q YLF WGMR to demonstrate and discuss this method.},
+ author = {Christensen, Josh T. and Azeem, Farhan and Trainor, Luke S. and Strekalov, Dmitry V. and Schwefel, Harald G. L.},
+ copyright = {© 2022 Optica Publishing Group},
+ doi = {10.1364/OL.474539},
+ file = {Submitted Version:/Users/harry/Zotero/storage/4YEB6B5D/Christensen et al. - 2022 - Distance calibration via Newton’s rings in yttrium.pdf:application/pdf},
+ issn = {1539-4794},
+ journal = {Optics Letters},
+ keywords = {Optical resonators, Whispering gallery modes, Total internal reflection, Single point diamond turning, Calibration, Solid state laser materials},
+ language = {EN},
+ month = {December},
+ note = {Publisher: Optica Publishing Group},
+ number = {23},
+ pages = {6053--6056},
+ title = {Distance calibration via Newton’s rings in yttrium lithium fluoride whispering gallery mode resonators},
+ url = {https://opg.optica.org/ol/abstract.cfm?uri=ol-47-23-6053},
+ urldate = {2022-11-22},
+ volume = {47},
+ year = {2022}
+}