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1.
A. V. Andreev S. Yu. Stremoukhov O. A. Shutova 《Journal of Experimental and Theoretical Physics》2010,111(6):936-948
Specific features of ionization of single atoms by laser fields of a near-atomic strength are investigated. Calculations are
performed for silver atoms interacting with femtosecond laser pulses with wavelengths λ = 800 nm (Ti:Sapphire) and λ = 1.064
μm (Nd:YAG). The dependences of the probability of ionization and of the form of the photoelectron energy spectra on the field
of laser pulses for various values of their duration are considered. It is shown that the behavior of the probability of ionization
in the range of subatomic laser pulse fields is in good agreement with the Keldysh formula. However, when the field strength
attains values close to the atomic field strength, the discrepancies in these dependences manifested in a decrease in the
ionization rate (ionization stabilization effect) or in its increase (accelerated ionization) are observed. These discrepancies
are associated with the dependence of the population dynamics of excited discrete energy levels of the atom on the laser pulse
field amplitude. 相似文献
2.
A theoretical analysis is presented of the effect of correlation between fluctuations of laser pulse amplitudes on population
transfer between the states of a three-level atom coupled by the laser field. The carrier frequencies of the pulses are tuned
to resonance with the transitions between the ground and excited states, |〈 and | 2〈, and the excited and metastable states,
|2〈 and |3〈, in a lambda-type configuration. The laser pulses are timed so that population transfer between states |1〈 and
| 3〈 is made possible by stimulated Raman adiabatic passage (STIRAP) in the absence of fluctuations. STIRAP does not occur
when the laser fields are not correlated. When the fluctuations of one pulse amplitude duplicate those of the other, STIRAP
can be observed for pulse amplitudes larger than those required in the absence of fluctuations. 相似文献
3.
B. Köhler U. Bäder A. Nebel J.-P. Meyn R. Wallenstein 《Applied physics. B, Lasers and optics》2002,75(1):31-34
We report on an injection-seeded 9.5-W 82-MHz-repetition-rate picosecond optical parametric generator (OPG) based on a 55 mm
long crystal of periodically poled lithium niobate (PPLN) with a quasi-phase-matching (QPM) grating period of 29.75 μm. The
OPG is excited by a continuously diode pumped mode-locked picosecond Nd:YVO4 oscillator-amplifier system. The laser system generates 7 ps pulses with a repetition rate of 82.3 MHz and an average power
of 24 W. Without injection-seeding the total average output power of the OPG is 8.9 W, which corresponds to an internal conversion
efficiency of 50%. The wavelengths of the signal and idler waves were tuned in the range 1.57–1.64 μm and 3.03–3.3 μm, respectively,
by changing the crystal temperature from 150 °C to 250 °C. Injection seeding of the OPG at 1.58 μm with 4 mW of single frequency
continuous-wave radiation of a distributed-feedback (DFB) diode laser increases the OPG output to 9.5 W (53% conversion efficiency).
The injection seeding increases the pulse duration and reduces the spectral bandwidth. When pumped by 10 W of 1.06 μm laser
radiation, the duration of the signal pulses increased from 3.6 ps to 5.5 ps while the spectral bandwidth is reduced from
4.5 nm to 0.85 nm. Seeding thus improved the time-bandwidth product from 1.98 to a value of 0.56, much closer to the Fourier
limit.
Received: 29 April 2002 / Published online: 8 August 2002 相似文献
4.
We describe an interferometric time-resolved photoemission technique that makes it possible to simultaneously observe the decay of optical induced polarizations and populations at surfaces in a two-color excitation scheme. In this scheme initially unoccupied electronic surface states are coherently excited by the interaction of laser pulses with frequency ωa and the two-photon polarization which is induced by laser pulses with frequency ωa/2. Interference is observed by changing the delay between both laser pulses using an actively stabilized two-color Mach–Zehnder interferometer. We demonstrate this technique for excitation of the n=1 image-potential state on a Cu(100) surface. PACS 78.47.+p; 79.60.Bm; 73.20.-r; 82.53.Kp; 42.50.Md 相似文献
5.
Bimal K. Deka 《International Journal of Infrared and Millimeter Waves》1985,6(12):1285-1294
The thresholds for CO2 laser induced breakdown and their variation with pulse width have been measured at various pressures for Ar, N2 and an 8/1/1 laser mixture of He/CO2/N2 using 3–40 ns duration pulses. These measurements indicate that excited state production plays a dominant role in determining the threshold for nanosecond duration pulses. This has been confirmed by the good agreement obtained between the measured and theoretical thresholds. 相似文献
6.
A method has been proposed to analyze the dynamics of interband two-photon absorption in a nonlinear medium excited by a sequence
of picosecond laser pulses of variable intensity and continuous probe radiation. Induced absorption leading both to hysteresis
in the dependence of the absorption on the intensity of laser pump radiation and to the opacity of crystals at the pump wavelength
has been revealed in initially transparent ZnWO4 and PbWO4 crystals irradiated by a train of 523.5-nm pulses with a duration of 20 ps at pump intensities of 5 to 140 GW/cm2. The kinetics of an increase in absorption and its subsequent relaxation at a 523.5-nm picosecond excitation of the crystals
have been measured with continuous 633-nm probe radiation. An exponential component of the increase in absorption with the
time constant τ = 2−3.5 and 8–9.5 μs depending on the direction of the linear polarization of pump radiation has been revealed
at 300 K in ZnWO4 and PbWO4 crystals, respectively. The absorption relaxation kinetics in the crystals are complicated and approach an exponential at
a late stage with the constant τ = 40−130 and 12–80 ms for the ZnWO4 and PbWO4 crystals, respectively. 相似文献
7.
A scheme for the construction of fiber laser systems for the generation of tunable ultrashort optical pulses is proposed.
The scheme is based on the self-Raman shift of the soliton frequency in dispersion-decreasing fibers with the subsequent spectral
broadening owing to the supercontinuum generation in a short highly nonlinear fiber and the compression in the corresponding
fiber compressor. An all-fiber laser system for the generation of ultrashort laser pulses in the wavelength range 1.6–2.0
μm is experimentally demonstrated. In particular, the shortest pulses with a duration of 24 fs are generated at wavelengths
of 1.8–1.9 μm, which corresponds to less than four optical cycles. 相似文献
8.
A miniaturized, high repetition rate, picosecond all solid state photo-induced distributed feedback (DFB) polymer-dye laser
is described by applying a passively Q-switched and frequency-doubled Cr4+:Nd3+:YAG-microchip laser (pulse width Δτ=540 ps, repetition rate ν=3 kHz, pump energy Epump=0.15 μJ) as a pump source. A poly-methylmethacrylate film doped with rhodamine B dye serves as active medium. The DFB-laser
pulses are temporally and spectrally characterized, and the stability of the thin polymer/dye film at high repetition rates
is analyzed. The shortest DFB-laser pulses obtained have a duration of 11 ps. After the emission of 350000 pulses the intensity
of the DFB-laser output has decreased by a factor of two and the pulse duration has increased by a factor of 1.2. For single
DFB-laser pulses of 20-ps duration the spectral bandwidth is measured to be Δλ=0.03 nm, which is only 0.005 nm above the calculated
Fourier limit assuming a Gaussian profile for the temporal shape of the pulses. Coarse wavelength tuning of the DFB laser
between 590 and 619 nm is done by turning the prism. Additionally, a fine tuning of the DFB-polymer-laser wavelength is achieved
by changing the temperature of the polymer/dye layer (=-0.05 nm/°C) in the range from 20 to 40 °C.
Received: 1 March 2001 / Revised version: 23 May 2001 / Published online: 18 July 2001 相似文献
9.
We report here an experimental study of the ionic keV X-ray line emission from magnesium plasma produced by laser pulses of
three widely different pulse durations (FWHM) of 45 fs, 25 ps and 3 ns, at a constant laser fluence of ∼1.5 × 104 J cm − 2. It is observed that the X-ray yield of the resonance lines from the higher ionization states such as H- and He-like ions
decreases on decreasing the laser pulse duration, even though the peak laser intensities of 3.5 × 1017 W cm − 2 for the 45 fs pulses and 6.2 × 1014 W cm − 2 for the 25 ps pulses are much higher than 5 × 1012 W cm − 2 for the 3 ns laser pulse. The results were explained in terms of the ionization equilibrium time for different ionization
states in the heated plasma. The study can be useful to make optimum choice of the laser pulse duration to produce short pulse
intense X-ray line emission from the plasma and to get the knowledge of the degree of ionization in the plasma. 相似文献
10.
A stretched-pulse mode-locked ytterbium-doped fiber laser was passively synchronized to a femtosecond Ti:sapphire laser at
a low repetition rate of 240 kHz through large cross absorption modulation along additional 1-m-long erbium-doped fiber. The
synchronous fiber laser with an ultra-long fiber cavity could produce not only nanosecond flat-top pulses with tunable pulse
duration but also Gaussian-shape stretched pulses with its minimum pulse duration of ∼450 ps as confirmed by cross-correlation
measurement. When operating in the stretched pulse regime, the sub-nanosecond fiber laser could be synchronously triggered
by the master injection with the cavity-length mismatch tolerance up to ∼7.8 cm and timing jitter less than 400 fs, confirming
that the stretched-pulse mode-locking of the ultra-long slave fiber laser could be robustly controlled by cross absorption
modulation effects in the erbium-doped fiber with appropriate femtosecond master injection. 相似文献
11.
A. L. Vikharev A. M. Gorbachev O. A. Ivanov V. A. Isaev S. V. Kuzikov B. Z. Movshevich J. L. Hirshfield S. H. Gold 《Radiophysics and Quantum Electronics》2008,51(7):539-555
We present the results of studies of the active compressor of 3-cm wavelength microwave pulses, which uses a high-Q storage
Bragg resonator excited at the H01 mode and new types of plasma switches. Phase variation during a compressed pulse and phase correlation of the input and compressed
microwave pulses are studied both experimentally and theoretically. Using a single-channel compressor excited at the megawatt
power level by the magnicon radiation with frequency 11.4 GHz, a power amplification factor equal to 9 was reached for an
output-pulse duration of 40–50 ns and a peak power of up to 25 MW.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 7, pp. 597–616, July 2008. 相似文献
12.
STM (scanning tunneling microscope) light emission from an evaporated Au film irradiated by pico second laser pulses has been investigated for various bias voltages of the STM. The observed emission consists of two components. The first component that has the same duration as the incident laser pulse is excited by laser induced tunneling electrons. The second component that has a longer duration than that of the laser pulse is emitted from surface polariton plasmons excited non-linearly by the laser pulse. 相似文献
13.
The presented theoretical model for a mode-locked Nd-glass laser simultaneously takes into account dynamics of the mode-locking
dye, amplification saturation and radiation background. A systematic variation of laser parameters gives insight into the
pulse formation process and allows to improve the laser design. The calculations show that it should be possible to decrease
considerably the duration of light pulses of a mode-locked Nd-glass laser. Using a new mode-locking dye with a switching time
of τ=2.7×10−12 s we obtained stable laser operation and a pulse duration of 1.7×10−12s. 相似文献
14.
We experimentally demonstrated a new few-cycle pulse compression technique through the cascade of bulk media and hollow-core
fiber (HCF) and this compression system has been intensively studied. The pulses with the duration of ∼5 fs and the energy
of 0.33 mJ near 800 nm have been generated by compressing the ∼40 fs input pulse from a commercial laser system. In principle,
this technique allows compression of pulses with duration of picoseconds to a few cycles (sub-7 fs) and the output can be
above 1 mJ. 相似文献
15.
A. Ya. Dzyublik 《JETP Letters》2010,92(3):130-134
We studied the decay of nuclear isomeric states in the field of the X-ray laser. The laser pulses are described by the Gaussian
wave packet of linearly polarized electromagnetic waves. At first stage the laser short pulse generates nuclear transition
in the intermediate excited state, which afterwards decays into the final state with emission of γ quantum. Simple formulas
are derived for the induced transition probability, which well correlate with known results, obtained previously for the incoherent
X-ray radiation. 相似文献
16.
The operation of a continuous-wave mode-locked silver gallium selenide (AgGaSe2) optical parametric oscillator (OPO) is reported. The OPO was synchronously excited by 120-fs-long pulses of 1.55-μm radiation
at a repetition rate of 82 MHz. The 1.55-μm radiation is generated by a noncritically phasematched cesium-titanyl-arsenate
(CTA)-OPO pumped by a mode-locked Ti:sapphire laser. The AgGaSe2-OPO generates signal and idler radiation in the range from 1.93 μm to 2.49 μm and from 4.1 μm to 7.9 μm, respectively. Up
to 67 mW of signal wave output power has been obtained. The experimentally determined pulse duration and chirp parameters
are in reasonable agreement with results from a numerical model taking into account group velocity mismatch, group velocity
dispersion, self phase modulation, and chirp enhancement.
Received: 6 August 1999 / Revised version: 4 October 1999 / Published online: 3 November 1999 相似文献
17.
D. Krennrich R. Knappe B. Henrich R. Wallenstein J.A. L’huillier 《Applied physics. B, Lasers and optics》2008,92(2):175-183
This paper reports on the generation of picosecond (ps) laser pulses by self-phase-adjusting additive-pulse-mode-locking (PSA)
at wavelengths of 0.9 and 1.3 μm. The main objective of this work was to investigate and compare the characteristic optical
properties of ps lasers based on different Nd-doped laser crystals like Nd:YAG, Nd:YAlO3, Nd:YVO4 and Nd:GdVO4. As a result of these investigations a mode-locked Nd:YVO4 laser for example, generated, ps pulses at 1.3 μm with a duration of 7 ps, a repetition rate of 160 MHz and an average power
of 4.7 W. At 0.9 μm pulses with a duration of 1.9 ps were obtained at a repetition rate of 158 MHz and an average power of
2.8 W.
PACS 42.70.Hj; 42.65.Re; 42.65.Ky 相似文献
18.
This paper presents the spectral emission and saturation properties of a Lumilass G9 fluorescence glass excited using a 157 nm laser emitting ∼10 ns duration pulses. This fluorescence glass can be applied in conjunction with a CCD array for beam profiling and divergence measurements. This method can also be used for deriving information on the spatial coherence function of the F2 laser. This constitutes one of the major contributions of the paper and is also discussed. 相似文献
19.
We suggest a protocol for quantum key distribution—a technology allowing two distant parties to create an unconditionally
secure cryptographic key. For the creation of the key we suggest to use laser pulses weakened to the single-photon level of
duration T, the pulse carrying the value “1” being shifted in time by T/2 compared to the pulse carrying the value “0”. The overlap of the pulses provides their non-orthogonality and, therefore,
impossibility to discriminate between them with certainty. Besides the signal pulses the protocol uses coherent decoy pulses,
having longer duration than the signal ones and providing a more effective protection from a wide class of attacks. Security
of the protocol is based on interferometric control of the pulse coherence at the receiving station. We analyze the security
of the protocol against a number of intercept-resend attacks and on the basis of this analysis substantiate the necessity
of decoy state implementation. 相似文献
20.
J.S. Robinson C.A. Haworth H. Teng R.A. Smith J.P. Marangos J.W.G. Tisch 《Applied physics. B, Lasers and optics》2006,85(4):525-529
We have investigated experimentally the energy transmission and spectral broadening of 30-fs, 700-μJ laser pulses in a neon-filled, 250-μm inner diameter hollow fibre. We implement a differentially pumped fibre, where a vacuum is maintained at the fibre entrance, and compare this to a statically filled fibre. We obtain significantly higher transmission and increased spectral broadening in the differentially pumped case due to a reduction of ionisation defocusing at the fibre entrance. This arrangement provides a method for the generation of near-transform- limited pulses with smoothly varying pulse duration whilst maintaining constant pulse energy, by simple adjustment of the gas pressure. Compression of ∼450-μJ pulses from the differentially pumped fibre to a duration of 6.5 fs has been achieved for pulses with spectra spanning 650–900 nm, by use of negatively dispersive chirped mirrors. PACS 42.65.Re; 42.65.Jx; 42.65.-k 相似文献