Analysis and detection of spatial coherence and frequency-locking in multi-mode lasers

2006 ◽  
Author(s):  
G. D'Alessandro ◽  
F. Papoff ◽  
T. Ackemann
Keyword(s):  
Spatial Coherence ◽  
Frequency Locking ◽  
Multi Mode

scholarly journals Asynchronous and Coherent Dynamics in Balanced Excitatory-Inhibitory Spiking Networks

2021 ◽  
Vol 15 ◽  
Author(s):  
Hongjie Bi ◽  
Matteo di Volo ◽  
Alessandro Torcini
Keyword(s):  
Spatial Scales ◽  
Spatial Coherence ◽  
Mean Field ◽  
Period Doubling ◽  
Structural Heterogeneity ◽  
Neural Mass Model ◽  
Current Fluctuations ◽  
Mass Model ◽  
Frequency Locking ◽  
Neural Mass

Dynamic excitatory-inhibitory (E-I) balance is a paradigmatic mechanism invoked to explain the irregular low firing activity observed in the cortex. However, we will show that the E-I balance can be at the origin of other regimes observable in the brain. The analysis is performed by combining extensive simulations of sparse E-I networks composed of N spiking neurons with analytical investigations of low dimensional neural mass models. The bifurcation diagrams, derived for the neural mass model, allow us to classify the possible asynchronous and coherent behaviors emerging in balanced E-I networks with structural heterogeneity for any finite in-degree K. Analytic mean-field (MF) results show that both supra and sub-threshold balanced asynchronous regimes are observable in our system in the limit N >> K >> 1. Due to the heterogeneity, the asynchronous states are characterized at the microscopic level by the splitting of the neurons in to three groups: silent, fluctuation, and mean driven. These features are consistent with experimental observations reported for heterogeneous neural circuits. The coherent rhythms observed in our system can range from periodic and quasi-periodic collective oscillations (COs) to coherent chaos. These rhythms are characterized by regular or irregular temporal fluctuations joined to spatial coherence somehow similar to coherent fluctuations observed in the cortex over multiple spatial scales. The COs can emerge due to two different mechanisms. A first mechanism analogous to the pyramidal-interneuron gamma (PING), usually invoked for the emergence of γ-oscillations. The second mechanism is intimately related to the presence of current fluctuations, which sustain COs characterized by an essentially simultaneous bursting of the two populations. We observe period-doubling cascades involving the PING-like COs finally leading to the appearance of coherent chaos. Fluctuation driven COs are usually observable in our system as quasi-periodic collective motions characterized by two incommensurate frequencies. However, for sufficiently strong current fluctuations these collective rhythms can lock. This represents a novel mechanism of frequency locking in neural populations promoted by intrinsic fluctuations. COs are observable for any finite in-degree K, however, their existence in the limit N >> K >> 1 appears as uncertain.

scholarly journals Asynchronous and coherent dynamics in balanced excitatory-inhibitory populations

2021 ◽  
Author(s):  
Hongjie Bi ◽  
Matteo di Volo ◽  
Alessandro Torcini
Keyword(s):  
Spatial Scales ◽  
Spatial Coherence ◽  
Period Doubling ◽  
Gamma Oscillations ◽  
Structural Heterogeneity ◽  
Neural Mass Model ◽  
Current Fluctuations ◽  
Mass Model ◽  
Frequency Locking ◽  
Neural Mass

Dynamic excitatory-inhibitory (E-I) balance is a paradigmatic mechanism invoked to explain the irregular low firing activity observed in the cortex. However, we will show that the E-I balance can be at the origin of other regimes observable in the brain. The analysis is performed by combining extensive simulations of sparse E-I networks composed of N spiking neurons with analytical investigations of low dimensional neural mass models. The bifurcation diagrams, derived for the neural mass model, allow to classify the possible asynchronous and coherent behaviours emerging in balanced E-I networks with structural heterogeneity for any finite in-degree K. In the limit N >> K >> 1 both supra and sub-threshold balanced asynchronous regimes can be observed in our system. Due to the heterogeneity the asynchronous states are characterized by the splitting of the neurons in three groups: silent, fluctuation and mean driven. These features are consistent with experimental observations reported for heterogeneous neural circuits. The coherent rhythms observed in our system can range from periodic and quasi-periodic collective oscillations (COs) to coherent chaos. These rhythms are characterized by regular or irregular temporal fluctuations joined to spatial coherence somehow similar to coherent fluctuations observed in the cortex over multiple spatial scales. The COs can emerge due to two different mechanisms. A first mechanism similar to the pyramidal-interneuron gamma (PING) one, usually invoked for the emergence of gamma-oscillations. The second mechanism is intimately related to the presence of current fluctuations, which sustain COs characterized by an essentially simultaneous bursting of the two populations. We observe period-doubling cascades involving the PING-like COs finally leading to the appearance of coherent chaos. Fluctuation driven COs are usually observable in our system as quasi-periodic collective motions characterized by two incommensurate frequencies. However, for sufficiently strong current fluctuations we report a novel mechanism of frequency locking among collective rhythms promoted by these intrinsic fluctuations. Our analysis suggest that despite PING-like or fluctuation driven COS are observable for any finite in-degree K, in the limit N >> K >> 1 these solutions finally result in two coexisting balanced regimes: an asynchronous and a fully synchronized one.

scholarly journals Possibilities of increase of gyrotron efficiency via frequency locking by external signal

2019 ◽  
Vol 30 ◽  
pp. 09004
Author(s):  
Vladimir L. Bakunin ◽  
Gregory G. Denisov ◽  
Yury M. Guznov ◽  
Michael V. Morozkin ◽  
Yulia V. Novozhilova ◽  
...  
Keyword(s):  
Electron Beam ◽  
Cyclotron Frequency ◽  
External Signal ◽  
Frequency Locking ◽  
Frequency Resonance ◽  
Efficiency Increase ◽  
Optimal Efficiency ◽  
Multi Mode

Possibility of efficiency increase of a gyrotron, which frequency is locked by an external monochromatic signal, is studied. Dependencies of orbital efficiency on cyclotron frequency resonance mismatch for different currents of the electron beam are found. It is shown that in multi-mode gyrotron there is a possibility of shifting of frequency-locking zone to the region of parameters corresponding to the optimal efficiency, so efficiency may be significantly increased compared to the free gyrotron.

Frequency locking and the loss of spatial coherence for driven space-charge domains in ultrapure Ge

1992 ◽  
Vol 46 (12) ◽  
pp. 7469-7478 ◽  
Author(s):  
A. M. Kahn ◽  
D. J. Mar ◽  
R. M. Westervelt
Keyword(s):  
Space Charge ◽  
Spatial Coherence ◽  
Frequency Locking

scholarly journals Application of a Novel Nd:YAG/PPMgLN Laser Module Speckle-Suppressed by Multi-Mode Fibers in an Exhibition Environment

Photonics ◽  
2022 ◽  
Vol 9 (1) ◽  
pp. 46
Author(s):  
Xiao Liu ◽  
Xin-Ting Zeng ◽  
Wen-Jian Shi ◽  
Shang-Feng Bao ◽  
Tao Yu ◽  
...  
Keyword(s):  
Image Quality ◽  
Spatial Coherence ◽  
Optical Components ◽  
Service Guarantee ◽  
Different Types ◽  
Laser Sources ◽  
Laser Module ◽  
Interactive Experience ◽  
Multi Mode ◽  
High Coherence

Laser exhibition technology has been widely used in the virtual environment of exhibitions and shows, as well as in the physical conference and exhibition centers. However, the speckle issue due to the high coherence of laser sources has caused harmful impacts on image quality, which is one of the obstacles to exhibition effects. In this paper, we design a compact Nd:YAG/PPMgLN laser module at 561.5 nm and use two different types of big-core multi-mode fibers to lower the spatial coherence. According to our experiment, the speckle contrasts relating to these two types reduce to 7.9% and 4.1%, respectively. The results of this paper contribute to improving the application effects of key optical components in the exhibitions. Only in this way can we provide technical supports and service guarantee for the development of the exhibition activities, and an immersive interactive experience for the audiences.

Quanitative aspects of electron diffraction using electron holography

1995 ◽  
Vol 53 ◽  
pp. 616-617
Author(s):  
E. Völkl ◽  
L.F. Allard ◽  
B. Frost ◽  
T.A. Nolan
Keyword(s):  
Electron Beam ◽  
Electron Diffraction ◽  
Software Package ◽  
Spatial Coherence ◽  
Electron Holography ◽  
Image Intensity ◽  
Interference Fringes ◽  
Complex Image ◽  
The Difference ◽  
Recorded Image

Off-axis electron holography has the well known ability to preserve the complex image wave within the final, recorded image. This final image described by I(x,y) = I(r) contains contributions from the image intensity of the elastically scattered electrons IeI (r) = |A(r) exp (iΦ(r)) |, the contributions from the inelastically scattered electrons IineI (r), and the complex image wave Ψ = A(r) exp(iΦ(r)) as:(1) I(r) = IeI (r) + Iinel (r) + μ A(r) cos(2π Δk r + Φ(r))where the constant μ describes the contrast of the interference fringes which are related to the spatial coherence of the electron beam, and Φk is the resulting vector of the difference of the wavefront vectors of the two overlaping beams. Using a software package like HoloWorks, the complex image wave Ψ can be extracted.

Multi-mode light microscopy of microtubule assembly dynamics and chromosome movement in vivo and In vitro

1996 ◽  
Vol 54 ◽  
pp. 730-731
Author(s):  
E. D. Salmon ◽  
J. C. Waters ◽  
C. Waterman-Storer
Keyword(s):  
Imaging System ◽  
Ccd Camera ◽  
Transmitted Light ◽  
Microtubule Assembly ◽  
Live Cells ◽  
Optical Efficiency ◽  
Multiple Band ◽  
Multi Mode

We have developed a multi-mode digital imaging system which acquires images with a cooled CCD camera (Figure 1). A multiple band pass dichromatic mirror and robotically controlled filter wheels provide wavelength selection for epi-fluorescence. Shutters select illumination either by epi-fluorescence or by transmitted light for phase contrast or DIC. Many of our experiments involve investigations of spindle assembly dynamics and chromosome movements in live cells or unfixed reconstituted preparations in vitro in which photodamage and phototoxicity are major concerns. As a consequence, a major factor in the design was optical efficiency: achieving the highest image quality with the least number of illumination photons. This principle applies to both epi-fluorescence and transmitted light imaging modes. In living cells and extracts, microtubules are visualized using X-rhodamine labeled tubulin. Photoactivation of C2CF-fluorescein labeled tubulin is used to locally mark microtubules in studies of microtubule dynamics and translocation. Chromosomes are labeled with DAPI or Hoechst DNA intercalating dyes.

Sign in / Sign up

Export Citation Format

Share Document