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1.
The mechanism of generation of terahertz radiation upon irradiation of a target by short (∼ 0.1 ns) high-intensity laser pulses
(I ∼ 1018−1019 W cm−2) is investigated by numerical simulation using the relativistic electromagnetic PIC code. The interaction of such a pulse
with the target, a plasma is formed on it. Electrons emitted from the plasma form a virtual cathode whose oscillations are
determined not only by their self-field, but also by the field of ions of the plasma. Generation occurs in the terahertz frequency
range with the efficiency thrice as high as in the absence of ions (i.e., with traditional reditron generation mechanism).
The explanation for this effect is also given. 相似文献
2.
I. I. Kalikinskii 《Technical Physics》1998,43(2):247-248
The energy of the radiation emitted by an ultrarelativistic (1 GeV) electron at a transition from vacuum into yttrium iron
garnet I3Fe5O12 at the ferromagnetic resonance frequency (vacuum wavelength 3 cm) is estimated. The energy at this frequency was found to
be 10−13 eV·s. If modern electron accelerators are used (particle current 10 mA), then for 1 s the energy at the ferromagnetic resonance
frequency will be of the order of 1 J·s, so that the effect could have practical applications.
Zh. Tekh. Fiz. 68, 122–123 (February 1998) 相似文献
3.
K. R. Allakhverdiev M. Ö. Yetis T. K. Baykara S. M. T. Özbek E. Yu. Salaev 《Laser Physics》2011,21(3):598-600
Two methods of preparation of the devices for visualization of pulsed and continuous near-IR (near infrared) are described
and the results of conversion of pulsed and continuous IR (800–1360 nm) laser radiation into the visible range of spectra
(400–680 nm) by using a transparent substrate covered with the particles (including nanoparticles) of effective nonlinear
materials of GaSe
x
S1 − x
(0.2 ≤ x ≤ 0.8) are presented. Converted light can be detected in transmission or reflection geometry as a visible spot corresponding
to the real size of the incident laser beam. Developed device structures can be used for checking if the laser is working
or not, for optical adjustment, for visualization of distribution of laser radiation over the cross of the beam and for investigation
of the content of the laser radiation. Low energy (power density) limit for visualization of the IR laser pulses with 2–3
ps duration for these device structures are: between 4.6–2.1 μJ (3 × 10−4−1 × 10−4 W/cm2) at 1200 nm; between 8.4–2.6 μJ (4.7 × 10−4−1.5 × 10−4 W/cm2) at 1300 nm; between 14.4–8.1 μJ (8.2 × 10−4–4.6 × 10−4 W/cm2) at 1360 nm. Threshold damage density is more than 10 MW/cm2 at λ = 1060 nm, pulse duration τ = 35 ps. The results are compared with commercially existing laser light visualizators. 相似文献
4.
The spatial and temporal development of the temperature and the electron density of a spark produced in He at 10 atm in the
focus of a lens by a mode-locked laser pulse having only 1.5 mJ energy have been investigated. Measuring the absolute intensity
of the continuum radiation emitted by the spark and the broadening of a Heii-line it can be concluded that local thermodynamic equilibrium has established 15 ns after the initiation of the plasma. At
this time a temperature of 65000 K and a maximum electron density of 1.4·1019 cm−3 was found with a pressure of 20 times the initial gas pressure. These values are in agreement with the values required for
an expansion model given in an earlier work basing on a radiation mechanism which explains the stepwise growth of a laser
spark under the influence of a train of mode-locked pulses. 相似文献
5.
G. V. Danilyan J. Klenke V. A. Krakhotin V. L. Kuznetsov V. V. Novitsky V. S. Pavlov P. B. Shatalov 《Physics of Atomic Nuclei》2009,72(11):1812-1817
Gamma rays probably emitted by the fissioning nucleus 236U* at the instant of the break of the neck or within the time of about 10−21 s after or before this were discovered in the experiment devoted to searches for the effect of rotation of the fissioning
nucleus in the process 235U($
\vec n
$
\vec n
, γf) and performed in a polarized beam of cold neutrons from the MEPHISTO Guideline at the FRM II Munich reactor. Detailed investigations
revealed that the angular distribution of these gamma rays is compatible with the assumption of the dipole character of the
radiation and that their energy spectrum differs substantially from the spectrum of prompt fission gamma rays. In the measured
interval 250–600 keV, this spectrum can be described by an exponential function at the exponent value of α = −5 × 10−3 keV−1. The mechanism of radiation of such gamma rays is not known at the present time. Theoretical models based on the phenomenon
of the electric giant dipole resonance in a strongly deformed fissioning nucleus or in a fission fragment predict harder radiation
whose spectrum differs substantially from the spectrum measured in the present study. 相似文献
6.
A sequential three-dimensional (3D) particle-in-cell simulation code PICPSI-3D with a user friendly graphical user interface
(GUI) has been developed and used to study the interaction of plasma with ultrahigh intensity laser radiation. A case study
of laser–plasma-based electron acceleration has been carried out to assess the performance of this code. Simulations have
been performed for a Gaussian laser beam of peak intensity 5 × 1019 W/cm2 propagating through an underdense plasma of uniform density 1 × 1019 cm − 3, and for a Gaussian laser beam of peak intensity 1.5 × 1019 W/cm2 propagating through an underdense plasma of uniform density 3.5 × 1019 cm − 3. The electron energy spectrum has been evaluated at different time-steps during the propagation of the laser beam. When the
plasma density is 1 × 1019 cm − 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~14 MeV, with an energy spread of ±7 MeV.
On the other hand, when the plasma density is 3.5 × 1019 cm − 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~23 MeV, with an energy spread of ±7.5 MeV. 相似文献
7.
V. D. Zvorykin A. O. Levchenko A. G. Molchanov I. V. Smetanin N. N. Ustinovskii 《Bulletin of the Lebedev Physics Institute》2010,37(2):60-64
The grazing mode of microwave propagation in a hollow plasma waveguide formed by ionization of atmospheric air with a small
easily ionized additive by strong UV pulses of the Garpun KrF laser (λ = 248 nm, the pulse duration and energy are ∼70 ns and ∼50 J) was experimentally demonstrated for the first time. The annular
laser beam produced a hollow tube ∼10 cm in diameter with an electron density of ∼1012 cm−3 in a plasma wall ∼1 cm thick, over whichmicrowave radiation with λ
mw
∼ 8 mm was transmitted to a distance of 60 m. Themicrowave signal transmitted by the waveguide was amplified by a factor
of 6 in comparison with propagation in free space. 相似文献
8.
V. M. Gordienko I. A. Makarov V. P. Petukhov A. S. Khomenko 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(2):183-188
The dependence of the characteristic X-ray radiation yield from CaF2 crystal on the formed microchannel depth under highly intensive (I ∼ 3 × 1015 W/cm2) laser pulses with different contrast was obtained. The maximum of the characteristic X-ray radiation yield at these experimental
conditions corresponded to the microchannel depth of 30–50 μm. The efficiency of the laser radiation conversion to the characteristic
X-ray radiation increased from 6 × 10−8 for the surface up to 10−7 in the microchannel. The dependence of the characteristic X-ray radiation yield on the viewing angle showed that the source
of X-ray radiation was located near the surface inside the microchannel. 相似文献
9.
Y. B. Kale A. Ray R. D’Souza Q. V. Lawande B. N. Jagatap 《Applied physics. B, Lasers and optics》2010,100(3):505-514
We here present a comparative study of frequency stabilities of pump and probe lasers coupled at a frequency offset generated
by coherent photon-atom interaction. Pump-probe spectroscopy of the Λ configuration in D2 transition of cesium is carried out to obtain sub-natural (∼2 MHz) electromagnetically induced transparency (EIT) and sub-Doppler
(∼10 MHz) Autler-Townes (AT) resonance. The pump laser is locked on the saturated absorption spectrum (SAS, ∼13 MHz) and the
probe laser is successively stabilized on EIT and AT signals. Frequency stabilities of pump and probe lasers are calculated
in terms of Allan variance σ(2,τ) by using the frequency noise power spectrum. It is found that the frequency stability of the probe stabilized on EIT is
superior (σ∼2×10−13) to that of SAS locked pump laser (σ∼10−12), whereas the performance of the AT stabilized laser is inferior (σ∼6×10−12). This contrasting behavior is discussed in terms of the theme of conventional master-slave offset locking scheme and the
mechanisms underlying the EIT and sub-Doppler AT resonances in a Doppler broadened atomic medium. 相似文献
10.
A. V. Dubrov V. D. Dubrov Y. N. Zavalov V. Y. Panchenko 《Applied physics. B, Lasers and optics》2011,105(3):537-543
The results of measurement of fluctuations of brightness temperature T in the region of exposure to laser radiation of a 3 mm-thick steel plate are presented. The local luminosity along the cut-front
was measured using two-color multichannel pyrometer. Cutting trials were carried out with CO2 laser (10.6 μm, 1200 W) and fiber laser (1.07 μm, 1800 W). Special attention was given to the frequency range of temperature
fluctuations above frequency of melt overflight, aiming on on-line monitoring applications. It is shown that local fluctuations
of T are related to local melt’s surface deformations due to unequal radiation absorption; thus the noise spectrum of T fluctuations reflects turbulent surface deformation, caused by gas jet and capillary waves. It is also shown that the thermo-capillary
effect with capillary-wave turbulence generation can be observed in case of exposure to 10.6 μm radiation with a laser intensity
of about 1 MW/cm2. The power law of “−7/6” describes the spectrum of the T fluctuation variance in this case of anomalous absorption of radiation, and the standard deviation of T is in excess of 10 K for a frequency of 14 kHz. There is no such effect in case of fiber-laser radiation applying, and the
source of the capillary waves is only forced low-frequency deformations of the melt surface. The standard deviation of T does not exceed 3 K on the frequency of 14 kHz, and above, and a power law of the spectrum fluctuation is described by about
“−3” in that range. 相似文献
11.
The results of an investigation of continuous frequency tuning of a neodymium laser in the UV and VUV ranges are reported.
Generation of the sum frequency of second harmonic radiation and the radiation from a parametric light generator in the UV
region (338–366 nm) is achieved. The optimal conditions for tuning UV radiation in the range 113.5–117.0 nm in third-harmonic
generation processes in xenon and its mixtures with other gases are investigated. A third-harmonic generation efficiency of
∼5×10−4 and a tuning range >2600 cm−1 are obtained in the VUV range investigated.
Zh. Tekh. Fiz. 68, 82–89 (May 1998) 相似文献
12.
M. L. Hamilton R. Peverall G. A. D. Ritchie L. J. Thornton J. H. van Helden 《Applied physics. B, Lasers and optics》2009,97(3):715-722
We have demonstrated the production of ∼1.9 μm near-infrared radiation by using difference frequency generation within a 5%
MgO doped PPLN crystal by coupling ∼735 nm radiation from a tunable external cavity diode laser with relatively high powered
532 nm radiation from both Nd:YVO3 and Nd:YAG lasers. The radiation produced is of low power, ∼15 μW, and was used in conjunction with the sensitivity enhancing
techniques of wavelength modulation spectroscopy (WMS) and cavity enhanced absorption spectroscopy (CEAS). Experiments were
carried out on rotationally resolved transitions in the combination bands of NH3 and CO2 in the 1.9 μm region. An α
min value of 3.6×10−6 cm−1 Hz−1/2 was achieved for WMS measurements on CO2. A comparable α
min value of 2.2×10−6 cm−1 Hz−1/2 was achieved for NH3 using CEAS. The low NIR power indicates that despite the level of MgO doping quoted for the crystal, under prolonged exposure
photorefractive damage has occurred. 相似文献
13.
An analytical model of K
α radiation of thin laser targets has been developed. It has been shown that, for such targets, the motion of fast electrons
is significant not only in the target itself but also in vacuum. The considered dependences for the free path length of a
fast electron and for the absorption coefficient of laser radiation on the laser intensity with allowance for the electron
motion in vacuum make it possible to match the results of the proposed model with the experimental data on generation of K
α radiation in wide ranges of laser intensities (1018–1021 W/cm2) and thicknesses (1–100 μm) of targets. 相似文献
14.
I. N. Konovalov 《Russian Physics Journal》2000,43(5):392-396
Experimental investigations have been performed for aXeCl laser with the active region aperture equal to 6.5×7 and 15×15 cm. To pump the laser, two types of generator were used: a
generator connected in a double-loop circuit with a peaking capacitor and a multichannel spark gap switch and a magnetic thyratron
generator. The working mixtureNe−Xe−HCl was preionized with soft x rays and a low-current electron beam, providing an initial electron density ranging from 106 to 5·1013 cm−3. Conditions in which a homogeneous space discharge is initiated have been studied. It has been investigated how the degree
of ionization of the gas and the aperture of the active region affect the discharge and lasing characteristics of the laser.
The laser efficiency reaches 4% with an energy of ≈ 6 J extracted from one liter of the active region.
Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh
Uchebnykh Zavedenii, Fizika, No. 5, pp. 54–59, April, 2000. 相似文献
15.
L. Lis 《Il Nuovo Cimento D》1985,5(5):451-463
Summary Competition between the 3391 radiation emitted by a long He−Ne tube and the 633 laser oscillations was investigated experimentally.
the results were analysed by means of the balance equations of populations. The absolute values of populations of the 5s′[1/2]
1
0
and 4p′[3/2]2 levels, the excitation rates of the levels and the rates of induced transitions were computed. A new experiment on the 3391
radiation generated by the long He−Ne tube showed a negligible value of the radiation in the middle of the tube.
Riassunto Si è studiata sperimentalmente la competizione tra la radiazione 3391 emessa da un lungo tubo a He−Ne e l'oscillazione dellaser 633. I risultati sono stati analizzati per mezzo dell'equazioni di bilanciamento delle popolazioni. Sono stati calcolati i valori assoluti delle popolazioni dei livelli 5s′[1/2] 1 0 e 4p′[3/2]2, i valori di eccitazione dei livelli e i valori delle transizioni indotte. Un nuovo esperimento sulla radiazione 3391 generata dal lungo tubo a He−Ne ha mostrato un valore trascurabile della radiazione nel centro del tubo.相似文献
16.
O. Terra G. Grosche K. Predehl R. Holzwarth T. Legero U. Sterr B. Lipphardt H. Schnatz 《Applied physics. B, Lasers and optics》2009,97(3):541-551
We have explored the performance of two “dark fibers” of a commercial telecommunication fiber link for a remote comparison
of optical clocks. The two fibers, linking the Leibniz University of Hanover (LUH) with the Physikalisch-Technische Bundesanstalt
(PTB) in Braunschweig, are connected in Hanover to form a total fiber length of 146 km. At PTB the performance of an optical
frequency standard operating at 456 THz was imprinted to a cw transfer laser at 194 THz, and its frequency was transmitted
over the fiber. In order to detect and compensate phase noise related to the optical fiber link we have built a low-noise
optical fiber interferometer and investigated noise sources that affect the overall performance of the optical link. The frequency
stability at the remote end has been measured using the clock laser of PTB’s Yb+ frequency standard operating at 344 THz.
We show that the frequency of a frequency-stabilized fiber laser can be transmitted over a total fiber length of 146 km with
a relative frequency uncertainty below 1×10−19, and short term frequency instability given by the fractional Allan deviation of σ
y
(τ)=3.3×10−15/(τ/s). 相似文献
17.
The retardation of the recombination of electrons and holes in semiconductors in an applied uniform magnetic field has been
predicted. It has been shown that the recombination time in germanium in the temperature range of T = 1–10 K at charge carrier densities of n
e
= 1010−1014 cm−3 in magnetic fields of B = 3 × 102−3 × 104 G can be more than two orders of magnitude larger than that at zero magnetic field. This means that, after creation of nonequilibrium
charge carriers by their injection at the p-n junction owing to some radiation sources or fast electron irradiation, the semiconductor retains its conductivity for a much
longer time at nonzero applied magnetic field. The effect under study can be used, for example, to detect radiation sources. 相似文献
18.
Summary The data of 46 months of the GEOGRAV gravitational-wave antenna are analysed to search for monochromatic Doppler-shifted signals
from rotating neutron stars, in the frequency band (856.2÷859.2) Hz. Two different methods were used. With the first, the
gravitational radiation from the whole sky is investigated and a limit ofh≤1·10−21 is found. With the second method only the radiation from a single source is searched. The Galactic Centre and the Large Magellanic
Cloud are considered as sources and the limit ofh≤6·10−22 is found. 相似文献
19.
G. G. Vertogradov V. P. Uryadov V. G. Vertogradov 《Radiophysics and Quantum Electronics》2007,50(1):1-7
We present the results of the ionosphere oblique chirp sounding on the Cyprus—Nizhny Novgorod, Cyprus—Rostov-on-Don, and Moscow—Rostov-on-Don
mid-latitude paths during X-ray flares in January 17, 19, and 20, 2005. It is found that during strong flares the blackout
of short radio waves was observed over the entire frequency range of chirp sounding on the Cyprus—Nizhny Novgorod and Cyprus—Rostov-on-Don
paths. Modeling of the electron-density profiles in the lower ionosphere based on absorption of short radio waves on the Moscow—Rostov-on-Don
path at different stages of the decay of the X-ray radiation intensity is carried out. It is shown that at the instant corresponding
to the maximum value of the flare radiation flux, the electron density in the lower ionosphere at altitudes 60–80 km increased
by a factor of about 10 and 100 for flares with radiation flux densities 5·10−2 and 3·10−1
erg/(cm
2·s) in the wavelength range 0.5–4.0 Å which took place in January 19 and 20, respectively.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 1, pp. 1–8, January 2007. 相似文献
20.
A. K. Dharmadhikari J. A. Dharmadhikari D. Mathur 《Applied physics. B, Lasers and optics》2009,94(2):259-263
Filamentation occurs within a 1.5 cm-long crystal of BaF2 during the propagation of intense, ultrashort (40 fs) pulses of 800 nm light; a systematic study as a function of incident
power enables us to extract quantitative information on laser intensity within the condensed medium, the electron density
and the six-photon absorption cross section. At low incident power, a single filament is formed within the crystal; two or
more filaments are observed along the direction transverse to laser propagation at higher incident powers. Further, due to
fluorescence from six-photon absorption (6PA), we are able to map the intensity variation in the focusing–refocusing cycles
along the direction of laser propagation. At still higher incident powers, we observe splitting of multiple filaments. By
measuring the radius (L
min ) of single filament inside BaF2, we obtain estimates of peak intensities (I
max ) and electron densities (ρ
max ) to be 3.26×1013 W cm−2 and 2.81×1019 cm−3, respectively. Use of these values enables us to deduce that the 6PA cross-section in BaF2 is 0.33×10−70 cm12 W−6 s−1. 相似文献