21 research outputs found
Rate Equation Theory for Organic Diode Laser and Experimental Validation with Microcavity OLED
We present a new model for an organic laser diode based on rate equations for polarons, singlet and triplet excitons, both in host and dopant molecules, and photon densities. The model is validated by comparing calculated optical responses with measurements on high-speed low-Q OLEDS under pulsed nanosecond electrical excitation. The model confirms the threshold-current density of ~500A/cm2 observed in the recent first experiment with indication of lasing in an OLED with DFB-grating in the group of Adachi [1], if the Q-factor ~20K and no residual absorption occurs
A Detection of Cosmological 21 cm Emission from CHIME in Cross-correlation with eBOSS Measurements of the Lyman- Forest
We report the detection of 21 cm emission at an average redshift in the cross-correlation of data from the Canadian Hydrogen Intensity
Mapping Experiment (CHIME) with measurements of the Lyman- forest from
eBOSS. Data collected by CHIME over 88 days in the ~MHz frequency band
() are formed into maps of the sky and high-pass delay filtered
to suppress the foreground power, corresponding to removing cosmological scales
with at the average redshift.
Line-of-sight spectra to the eBOSS background quasar locations are extracted
from the CHIME maps and combined with the Lyman- forest flux
transmission spectra to estimate the 21 cm-Lyman- cross-correlation
function. Fitting a simulation-derived template function to this measurement
results in a detection significance. The coherent accumulation of the
signal through cross-correlation is sufficient to enable a detection despite
excess variance from foreground residuals times brighter than the
expected thermal noise level in the correlation function. These results are the
highest-redshift measurement of \tcm emission to date, and set the stage for
future 21 cm intensity mapping analyses at
CHIME/FRB Discovery of 25 Repeating Fast Radio Burst Sources
We present the discovery of 25 new repeating fast radio burst (FRB) sources
found among CHIME/FRB events detected between 2019 September 30 and 2021 May 1.
The sources were found using a new clustering algorithm that looks for multiple
events co-located on the sky having similar dispersion measures (DMs). The new
repeaters have DMs ranging from 220 pc cm to 1700 pc
cm, and include sources having exhibited as few as two bursts to as many
as twelve. We report a statistically significant difference in both the DM and
extragalactic DM (eDM) distributions between repeating and apparently
nonrepeating sources, with repeaters having lower mean DM and eDM, and we
discuss the implications. We find no clear bimodality between the repetition
rates of repeaters and upper limits on repetition from apparently nonrepeating
sources after correcting for sensitivity and exposure effects, although some
active repeating sources stand out as anomalous. We measure the repeater
fraction and find that it tends to an equilibrium of % over
our exposure thus far. We also report on 14 more sources which are promising
repeating FRB candidates and which merit follow-up observations for
confirmation.Comment: Submitted to ApJ. Comments are welcome and follow-up observations are
encouraged
Sub-second periodicity in a fast radio burst
Fast radio bursts (FRBs) are millisecond-duration flashes of radio waves that
are visible at distances of billions of light-years. The nature of their
progenitors and their emission mechanism remain open astrophysical questions.
Here we report the detection of the multi-component FRB 20191221A and the
identification of a periodic separation of 216.8(1) ms between its components
with a significance of 6.5 sigmas. The long (~3 s) duration and nine or more
components forming the pulse profile make this source an outlier in the FRB
population. Such short periodicity provides strong evidence for a neutron-star
origin of the event. Moreover, our detection favours emission arising from the
neutron-star magnetosphere, as opposed to emission regions located further away
from the star, as predicted by some models.Comment: Updated to conform to the accepted versio
Theoretical and experimental studie of ”-OLED on coplanar waveguide electrodes in nanosecond scale pulses width under high current densities
Ce travail de thĂšse explore lâexcitation Ă©lectrique de micro-OLEDs en rĂ©gime dâimpulsion afin dâĂ©valuer la possibilitĂ© dâatteindre le seuil laser dans les diodes laser organiques qui restent encore Ă dĂ©montrer. Ilsâagit dâidentifier des solutions scientifiques et techniques ouvrant la voie vers des densitĂ©s dâexcitations Ă©lectriques Ă©quivalentes aux seuils laser observĂ©s en pompage optique. Dans la littĂ©rature, les seuils les plus bas sont Ă©quivalents Ă des densitĂ©s de courant entre 0.72 et 4kA/cmÂČ si on suppose une efficacitĂ© quantique externe de 1%. De telles densitĂ©s de courant imposent un rĂ©gime dâexcitation Ă©lectrique impulsionnel pour sâaffranchir des risques de destructions par effet thermique et des pertes par annihilation singulet-triplet dĂšs lors que lâon travaille avec des durĂ©es dâimpulsion de lâordre de la nanoseconde. Et pour espĂ©rer des rĂ©ponses Ă©lectriques et optiques efficaces Ă de telles durĂ©es dâimpulsions, il est proposĂ© ici de combiner lâĂ©lectronique hyperfrĂ©quence et lâoptoĂ©lectronique organique. A cet effet, un modĂšle Ă©lectrique Ă©quivalent de lâOLED permettant dâaccĂ©der Ă son temps de rĂ©ponse en mode tout-ou-rien est dĂ©veloppĂ©. De plus, des Ă©lectrodes spĂ©cifiques sont dimensionnĂ©es et structurĂ©es sous forme de lignes coplanaires dâimpĂ©dance caractĂ©ristique 50Ω afin de maĂźtriser lâimpĂ©dance du circuit dâexcitation et dâassurer le transfert du maximum dâĂ©nergie de lâimpulsion dâexcitation vers celui-ci. AprĂšs dĂ©pĂŽts de lâhĂ©tĂ©ro-structure organique basĂ©e sur le systĂšme hĂŽte-dopant Alq3:DCM, les composants ainsi rĂ©alisĂ©s sont caractĂ©risĂ©s Ă©lectriquement et optiquement avec diffĂ©rentes techniques par analyse vectorielle, en rĂ©gime continu et en rĂ©gime dâimpulsion. En rĂ©gime dâimpulsion de trĂšs courtes durĂ©es (2.5~20ns) et Ă faible taux de rĂ©pĂ©tition (100Hz), des temps de rĂ©ponse de 330ps etdes densitĂ©s de courant maximales entre 4 et 6kA/cmÂČ ont Ă©tĂ© mesurĂ©s alors que le maximum de luminance culmine Ă 4.11x10ⶠcd/mÂČ.This thesis explores the pulsed electrical excitation of micro-OLEDs in order to evaluate the possibility of reaching the laser threshold in organic laser diodes that have not yet be demonstrated. The main goal is the identification of the scientific and technical solutions towards high electrical excitation current densities equivalent to the laser thresholds observed under optical pumping. In the literature, the lowest reported thresholds are equivalent to current densities between 0.72 and 4kA/cmÂČ, assuming an external quantum efficiency of 1%. Such current densities imply a pulsed electrical excitation regime to prevent the risks of device breakdown by Joule heating effects and to avoid losses by excitons annihilation processes, as long as the pulses duration are in nanosecond range. To expect efficient electrical and optical responses to such pulse durations, it is suggested to combine microwave electronics and organic optoelectronics. For this purpose, an equivalent electrical model of the organic light emitting device, allowing access to its on-off mode time response, is developed. Additionally, specific electrodes are designed and patterned in the coplanar waveguide configuration with characteristic impedance of 50Ω, inorder to control the impedance of the excitation circuit and to ensure the maximum energy transfer of the excitation pulse to the device. After deposition of organic hetero-structure based on the Alq3:DCM host-guest system, the device is characterized electrically and optically with different techniques by vector network analysis, in continuous mode and in pulse mode. In pulse excitation regime with very short pulses durations (2.5~20ns) and low repetition rate (100Hz), time response of 330ps and maximum current densities between 4 and 6kA/cmÂČ are recorded while the maximum of luminance peaks at 4.11x10ⶠcd/mÂČ
Etude théorique et expérimentale de micro-OLEDs rapides sur électrodes coplanaires en régime d'impulsions à haute densité de courant
This thesis explores the pulsed electrical excitation of micro-OLEDs in order to evaluate the possibility of reaching the laser threshold in organic laser diodes that have not yet be demonstrated. The main goal is the identification of the scientific and technical solutions towards high electrical excitation current densities equivalent to the laser thresholds observed under optical pumping. In the literature, the lowest reported thresholds are equivalent to current densities between 0.72 and 4kA/cmÂČ, assuming an external quantum efficiency of 1%. Such current densities imply a pulsed electrical excitation regime to prevent the risks of device breakdown by Joule heating effects and to avoid losses by excitons annihilation processes, as long as the pulses duration are in nanosecond range. To expect efficient electrical and optical responses to such pulse durations, it is suggested to combine microwave electronics and organic optoelectronics. For this purpose, an equivalent electrical model of the organic light emitting device, allowing access to its on-off mode time response, is developed. Additionally, specific electrodes are designed and patterned in the coplanar waveguide configuration with characteristic impedance of 50Ω, inorder to control the impedance of the excitation circuit and to ensure the maximum energy transfer of the excitation pulse to the device. After deposition of organic hetero-structure based on the Alq3:DCM host-guest system, the device is characterized electrically and optically with different techniques by vector network analysis, in continuous mode and in pulse mode. In pulse excitation regime with very short pulses durations (2.5~20ns) and low repetition rate (100Hz), time response of 330ps and maximum current densities between 4 and 6kA/cmÂČ are recorded while the maximum of luminance peaks at 4.11x10ⶠcd/mÂČ.Ce travail de thĂšse explore lâexcitation Ă©lectrique de micro-OLEDs en rĂ©gime dâimpulsion afin dâĂ©valuer la possibilitĂ© dâatteindre le seuil laser dans les diodes laser organiques qui restent encore Ă dĂ©montrer. Ilsâagit dâidentifier des solutions scientifiques et techniques ouvrant la voie vers des densitĂ©s dâexcitations Ă©lectriques Ă©quivalentes aux seuils laser observĂ©s en pompage optique. Dans la littĂ©rature, les seuils les plus bas sont Ă©quivalents Ă des densitĂ©s de courant entre 0.72 et 4kA/cmÂČ si on suppose une efficacitĂ© quantique externe de 1%. De telles densitĂ©s de courant imposent un rĂ©gime dâexcitation Ă©lectrique impulsionnel pour sâaffranchir des risques de destructions par effet thermique et des pertes par annihilation singulet-triplet dĂšs lors que lâon travaille avec des durĂ©es dâimpulsion de lâordre de la nanoseconde. Et pour espĂ©rer des rĂ©ponses Ă©lectriques et optiques efficaces Ă de telles durĂ©es dâimpulsions, il est proposĂ© ici de combiner lâĂ©lectronique hyperfrĂ©quence et lâoptoĂ©lectronique organique. A cet effet, un modĂšle Ă©lectrique Ă©quivalent de lâOLED permettant dâaccĂ©der Ă son temps de rĂ©ponse en mode tout-ou-rien est dĂ©veloppĂ©. De plus, des Ă©lectrodes spĂ©cifiques sont dimensionnĂ©es et structurĂ©es sous forme de lignes coplanaires dâimpĂ©dance caractĂ©ristique 50Ω afin de maĂźtriser lâimpĂ©dance du circuit dâexcitation et dâassurer le transfert du maximum dâĂ©nergie de lâimpulsion dâexcitation vers celui-ci. AprĂšs dĂ©pĂŽts de lâhĂ©tĂ©ro-structure organique basĂ©e sur le systĂšme hĂŽte-dopant Alq3:DCM, les composants ainsi rĂ©alisĂ©s sont caractĂ©risĂ©s Ă©lectriquement et optiquement avec diffĂ©rentes techniques par analyse vectorielle, en rĂ©gime continu et en rĂ©gime dâimpulsion. En rĂ©gime dâimpulsion de trĂšs courtes durĂ©es (2.5~20ns) et Ă faible taux de rĂ©pĂ©tition (100Hz), des temps de rĂ©ponse de 330ps etdes densitĂ©s de courant maximales entre 4 et 6kA/cmÂČ ont Ă©tĂ© mesurĂ©s alors que le maximum de luminance culmine Ă 4.11x10ⶠcd/mÂČ
Ultra-short optical pulse generation and laser perspective in an Alq3 based micro OLED
We report experimental and theoretical investigations with high-speed ”-OLEDs and demonstrate promising optical pulse responses as short as 400 ps using Alq3. These observations indicate that high-speed ”-OLEDs can be used for light communication in the GHz regime. The measurements are for in-house fabricated ”-OLEDs without cavity and size of 100 ”m x 100 ”m. With a validated model for an electrically pumped OLED, we simulate the generation of ultra-short optical pulses. The model includes Stoke-shifted reabsorption and field-enhanced Langevin recombination rate. For the Alq3 system we compare the results with the above-mentioned measurements. The good agreement between the measurement and the simulation is the basis for further study of the prospects for ultra-short dynamics and organic laser diode operation on the ps time scale.</p
An organic laser diode model:a comparison between numerical and experimental dynamical responses in the high-current density nanosecond pulse regime below threshold
Recently, Adachi and co-workers have reported convincing proof of stimulated emission in an organic hetero-structure under electrical excitation [1]. This new organic laser diode opens a new era in the field of\u3cbr/\u3elasing with solid-state organic materials that covers the whole visible spectrum and can be patterned more easily than conventional III-V materials. This new device combines properties from dye-lasers and diode laser, and thus will also open new research in the field of laser dynamics with promising new and interesting behavior.\u3cbr/\u3eIn this study we propose a first organic laser diode model, and we check its validity by comparing the numerical results with experimental measurements acquired in the nanosecond pulsed regime below threshold. For the first time, we identify one parameters of the model that has been underestimated
Ultra-short optical pulse generation in micro OLEDs and the perspective of lasing
We report experimental and theoretical investigations with an in-house fabricated tris(8-hydroxyquinoline)-aluminum (Alq3)-based high-speed micro-organic light-emitting diodes (Ό-OLEDs) and demonstrate very promising optical pulse responses as short as 400 ps. With a model for an electrically pumped OLED, we simulate the emission of sub-nanosecond optical pulses. The model includes field-dependent (Poole-Frenkel) Langevin recombination and reabsorption of photons by singlets (Stokes-shifted), and by triplets (TA). The good agreement between the measurement and the simulation is the basis for further study of the prospects on the ps time scale, i.e. stimulated emission and conditions for laser operation. For an Alq3-based micro-OLED with high-Q optical cavity, we predict pulsed laser operation with damped relaxation oscillations in the GHz regime and several orders of magnitude linewidth narrowing, but only during 3 ns at most. The simulated current density threshold values vary from 10 kA cm-2 for Q= 500 to less than 1 kA cm-2 for Q = 1000. No continuous-wave (CW) lasing is found due to the accumulation of triplet excitons for t > 5 ns, which has two deteriorating effects, (a) suppression of the gain-providing singlet excitons due to singlet-triplet absorption and (b) suppression of the photon density due to photon absorption by triplets (TA). Prospects for CW-lasing with other organic molecules are discussed
Organic diode laser dynamics: Rate-equation model, reabsorption, validation and threshold predictions
We present and analyze a simple model based on six rate equations for an electrically pumped organic diode laser. The model applies to organic host-guest systems and includes Stoke-shifted reabsorption in a self-consistent manner. With the validated model for the Alq3:DCM host-guest system, we predict the threshold for short-pulse laser operation. We predict laser operation characterized by damped relaxation oscillations in the GHz regime and several orders of magnitude linewidth narrowing. Prospect for CW steady-state laser operation is discussed