Excitation of electrostatic waves at the beat frequency of two laser beams in a semiconductor plasma

1998 ◽  
Vol 20 (9) ◽  
pp. 1327-1336
Author(s):  
A. A. Mamun ◽  
C. A. Mendoza-Briceño
2011 ◽  
Vol 2011 ◽  
pp. 1-8
Author(s):  
Kengo Murasawa ◽  
Koki Sato ◽  
Takehiko Hidaka

A method for measuring frequencies of the terahertz (THz) radiation emitted by the antenna mounted on the photoconductive (PC) device is presented. Two laser beams with slightly different frequencies irradiate the PC device, producing a beat current of 1 THz in the photocurrent. A microwave signal is applied to the antenna electrode. The frequency of the THz wave is measured using the homodyne detection of the optical beat with the high-order harmonics of the microwave. It is being investigated that the high-order harmonics are produced by the PC device owing to its nonlinearity. Periodic peaks generated by the homodyne detection were observed in the photocurrent, as the microwave was swept from 16 to 20 GHz with a power of −40 dBm. Using the peak frequencies, the THz-wave frequency was determined to be  GHz. The measurement error is estimated to be less than 0.43 GHz. The proposed method realizes a compact frequency meter in the THz region.


2019 ◽  
Vol 37 (4) ◽  
pp. 415-427
Author(s):  
Gunjan Purohit ◽  
Vinod Rawat ◽  
Priyanka Rawat

AbstractAn analytical and numerical study has been carried out for the generation of terahertz (THz) radiation by beating of two intense cosh-Gaussian laser beams (decentered Gaussian beams) in the rippled density magnetized plasma under the relativistic–ponderomotive regime. In this process, both laser beams exert a relativistic–ponderomotive force on plasma electrons at the beat frequency and impart them an oscillatory velocity in the presence of a static magnetic field. Due to coupling between this nonlinear oscillatory velocity with density ripple, nonlinear current is generated that excites the THz radiation at the different frequency. Higher-order paraxial-ray approximation (non-paraxial theory) has been used in this study. The effects of the decentered parameter, magnetic field, and density ripple on the THz radiation generation in ripple density magnetized plasma have been investigated. Further, the effect of beating of laser beams on the THz field amplitude and the efficiency of THz radiation have been studied. The amplitude and efficiency of the emitted radiation are found to be highly sensitive to the decentered parameter, magnetic field, and density ripple. It has been found that the amplitude and efficiency of the generated THz radiation increase significantly with increasing the values of decentered parameter, magnetic field, and density ripple.


1974 ◽  
Vol 52 (22) ◽  
pp. 2223-2227 ◽  
Author(s):  
C. E. Capjack ◽  
C. R. James

The plasma power absorbed from a beat frequency wave generated through the nonlinear mixing of two laser beams may be optimized by the utilization of an electron current resonance. The parametric dependence of the plasma power absorption near an electron resonance is examined together with experimental considerations for the case where CO2 lasers are used.


1975 ◽  
Vol 53 (23) ◽  
pp. 2606-2610 ◽  
Author(s):  
C. E. Capjack ◽  
C. R. James

The heating of magnetized plasmas through the utilization of a beat frequency harmonic which is excited at a frequency near to that of a Langmuir mode in the plasma is examined. Heating rates are obtained for plasmas with temperatures in the range 1 eV to 10 000 eV. In addition, the effects of the plasma density and the mixing angle of the laser beams on the heating rate will be examined.


2018 ◽  
Vol 36 (2) ◽  
pp. 236-245 ◽  
Author(s):  
Prateek Varshney ◽  
Ajit Upadhayay ◽  
K. Madhubabu ◽  
Vivek Sajal ◽  
J. A. Chakera

AbstractWe propose a scheme for terahertz (THz) radiation generation by non-linear mixing of two cosh-Gaussian laser beams in axially magnetized plasma with spatially periodic density ripple where electron-neutral collisions have been taken into account. The laser beams exert a non-linear ponderomotive force due to spatial non-uniformity in the intensity. The plasma electrons acquire non-linear oscillatory velocity under the influence of ponderomotive force. This oscillatory velocity couples with preformed density ripples (n′ = n0αeiαz) to generate a strong transient non-linear current that resonantly derives THz radiation of frequency ~ωh (upper hybrid frequency). Laser frequencies (ω1 and ω2) are chosen such that the beat frequency (ω) lies in the THz region. The periodicity of density ripple provides phase-matching conditions (ω = ω1 − ω2 and $\vec k = \vec k_1 - \vec k_2 + {\rm \vec \alpha} $) to transfer maximum momentum from laser to THz radiation. The axially applied external magnetic field can be utilized to enhance the non-linear coupling and control various parameters of generated THz wave. The effects of decentered parameters (b), collisional frequency (νen), and magnetic field strength (B0 = ωcm/e) are analyzed for strong THz radiation generation. Analytical results show that the amplitude of THz wave enhances with decentered parameters as well as with the magnitude of axially applied magnetic field. The THz amplitude is found to be highly sensitive to collision frequency.


Author(s):  
Robert Hard ◽  
Gerald Rupp ◽  
Matthew L. Withiam-Leitch ◽  
Lisa Cardamone

In a coordinated field of beating cilia, the direction of the power stroke is correlated with the orientation of basal body appendages, called basal feet. In newt lung ciliated cells, adjacent basal feet are interconnected by cold-stable microtubules (basal MTs). In the present study, we investigate the hypothesis that these basal MTs stabilize ciliary distribution and alignment. To accomplish this, newt lung primary cultures were treated with the microtubule disrupting agent, Colcemid. In newt lung cultures, cilia normally disperse in a characteristic fashion as the mucociliary epithelium migrates from the tissue explant. Four arbitrary, but progressive stages of dispersion were defined and used to monitor this redistribution process. Ciliaiy beat frequency, coordination, and dispersion were assessed for 91 hrs in untreated (control) and treated cultures. When compared to controls, cilia dispersed more rapidly and ciliary coordination decreased markedly in cultures treated with Colcemid (2 mM). Correlative LM/EM was used to assess whether these effects of Colcemid were coupled to ultrastructural changes. Living cells were defined as having coordinated or uncoordinated cilia and then were processed for transmission EM.


Author(s):  
Edna S. Kaneshiro

It is currently believed that ciliary beating results from microtubule sliding which is restricted in regions to cause bending. Cilia beat can be modified to bring about changes in beat frequency, cessation of beat and reversal in beat direction. In ciliated protozoans these modifications which determine swimming behavior have been shown to be related to intracellular (intraciliary) Ca2+ concentrations. The Ca2+ levels are in turn governed by the surface ciliary membrane which exhibits increased Ca2+ conductance (permeability) in response to depolarization. Mutants with altered behaviors have been isolated. Pawn mutants fail to exhibit reversal of the effective stroke of ciliary beat and therefore cannot swim backward. They lack the increased inward Ca2+ current in response to depolarizing stimuli. Both normal and pawn Paramecium made leaky to Ca2+ by Triton extrac¬tion of the surface membrane exhibit backward swimming only in reactivating solutions containing greater than IO-6 M Ca2+ Thus in pawns the ciliary reversal mechanism itself is left operational and only the control mechanism at the membrane is affected. The topographic location of voltage-dependent Ca2+ channels has been identified as a component of the ciliary mem¬brane since the inward Ca2+ conductance response is eliminated by deciliation and the return of the response occurs during cilia regeneration. Since the ciliary membrane has been impli¬cated in the control of Ca2+ levels in the cilium and therefore is the site of at least one kind of control of microtubule sliding, we have focused our attention on understanding the structure and function of the membrane.


1985 ◽  
Vol 132 (3) ◽  
pp. 191 ◽  
Author(s):  
Luk Kwai-Man ◽  
Yu Ping-Kong
Keyword(s):  

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