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1.
More than thirty rotational lines equally spaced by 587 cm–1 are generated simultaneously in the vicinity of the fundamental line by four-wave Raman mixing using a high-power picosecond Ti:Sapphire laser as a pump source and hydrogen as a Raman medium. Since the wavelength of this multifrequency laser emission extends from the near-infrared to the near-ultraviolet, it can be utilized as a tunable light source for picosecond spectroscopy. Because of the wide spectral bandwidth available, this procedure has great potential for the generation of ultrashort laser pulses by mode-locking these emission lines. 相似文献
2.
D. Voelkel Yu.L. Chuzavkov J. Marquez S.N. Orlov Yu.N. Polivanov V.V. Smirnov F. Huisken 《Applied physics. B, Lasers and optics》1997,65(1):93-99
2 H2), methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) in a cell under equilibrium conditions and cooled in free jet expansions. For methane at room temperature the detection
limit was 2×1012 molecules per cm3 and quantum state, enabling the detection of trace species with a spatial resolution of 1 mm2×30 mm. In an attempt to study transitions in the ν1+ν3 and 2ν2+ν3 combination bands of CO2 or N2O, it was not possible to observe any DFWM signal. Instead a surprisingly strong, backward- and forward-directed emission
was found which could not be attributed to the DFWM process. The signal arising from this emission was more than 2 orders
of magnitude stronger than the DFWM signals obtained for other molecules. The frequencies of the emitted radiation were found
to correlate with the transitions ν1+ν3→ν1 and 2ν2+ν3→2ν2, respectively. Our investigations lead to the conclusion that the emission can be explained by stimulated Raman scattering,
resonantly enhanced by transitions to the combination levels ν1+ν3 and 2ν2+ν3.
This process seems to suppress the generation of DFWM signals.
Received: 1 October 1996/Revised version: 6 January 1997 相似文献
3.
4.
When a two-color laser beam is introduced into pressurized hydrogen, about 40 laser emission lines are generated from the ultraviolet to the visible regions. This phenomenon is ascribed to the stimulated Raman effect due to a combination ofJ=1 J=3 rotational andv=0 v=1 vibrational transitions. By introducing the two-color laser beam, the threshold for generation of the rotational line is substantially reduced. The present phenomenon is attributed to four-wave mixing, which allows efficient generation of higher-order rotational and vibrational Raman lines. 相似文献
5.
uv
vac=351.165 nm) of a ps 1 kHz Nd:YLF laser system is frequency tripled in xenon and mercury vapour. About 4×104 photons per pulse, i.e. 4×107 photons/s, are generated in xenon yielding a conversion efficiency of η=3×10-10. The unusual frequency tripling in xenon takes place in a positive dispersive wavelength region. It is shown that Kerr-induced
dispersion in the atomic system and a fifth-order process rather than a third-order process can explain the frequency tripling.
For comparison a four-wave mixing process is investigated in negative dispersive mercury vapour. Due to absorption of the
generated VUV radiation in the autoionization region of mercury the observed effective efficiency is, in our experimental
arrangement, even lower than in xenon. An analysis of the VUV generation with respect to absorption is given.
Received: 1 September 1997 相似文献
6.
An intense and monochromatic laser beam consisting of more than 40 vibrational and rotational lines is generated by the stimulated Raman effect, when two-color laser beams separated by 590 cm–1 are tightly focused into pressurized hydrogen. This phenomenon is reasonably explained by four-wave mixing; one beam is used for two-step excitation (1+1) to an imaginary level and another beam (2) acts as a seed beam, generating a fourth beam (21–2). Through cascade processes, so many laser emissions appear with a frequency difference of (1–2) in entire ultraviolet and visible regions. 相似文献
7.
8.
We investigate the effect of beam coherence on four-wave mixing via reflection gratings in photorefractive media. For the
case of phase conjugation, the results of our theoretical analysis indicate that partial coherence always leads to a drop
of signal gain and phase conjugate reflectivity in non-depleted cases. In general, the mutual coherence of the signal beam
and the pump beam can be enhanced due to the process of wave mixing. The mutual coherence of the phase conjugate beam and
one of the pump beams depends on the beam intensity ratio as well as the optical path difference. This is distinctly different
from the four-wave mixing case with a transmission grating.
Received: 15 October 1999 / Revised version: 26 June 2000 / Published online: 7 February 2001 相似文献
9.
A. Bolovinos S. Cohen A. Lyras C. Skordoulis T. Mikropoulos S. Assimopoulos 《Applied physics. B, Lasers and optics》1997,64(4):451-458
. The dependence of the reflectivity on the vapour density, the buffer gas pressure and the pump beams intensity was investigated.
The influence of the strong linear absorption was taken into account in a theoretical model that led to a satisfactory interpretation
of the experimental results. A maximum reflectivity of 46% was measured under optimized conditions. The effect was also studied
through the high-lying bound states . The maximum measured reflectivity was as high as for the first excited state. The effect of the oscillator strength on the
reflectivity was demonstrated experimentally and interpreted with the help of a simple theoretical model.
Received: 11 June 1996 相似文献
10.
Received: 20 June 1997/Revised version: 26 January 1998 相似文献
11.
2 Σ+,H′ 2Π±(v′=2), and 4dσ,πO2Σ+,O′ 2Π±(v′=0) Rydberg states of NO molecules are described. The analyses of the two-photon excitation functions and infrared emission
spectra revealed that only the 2Π- component was involved in PFWM. This is in good accordance with the absence of amplified spontaneous emission (ASE) in the
2Σ+ and 2Π+ components due to their predissociative character. Results provide some support for the mechanism that the generation of
the vacuum ultraviolet radiation was brought by PFWM in which ASE served as a third driving wave.
Received: 6 January 1998 相似文献
12.
Generation of UV and VIS laser light by stimulated Raman scattering in H2, D2, and H2/He using a pulsed Nd:YAG laser at 355 nm 总被引:3,自引:0,他引:3
A.D. Papayannis G.N. Tsikrikas A.A. Serafetinides 《Applied physics. B, Lasers and optics》1998,67(5):563-568
2 ), deuterium (D2), and mixtures of hydrogen and helium (H2/He), versus Raman gas pressure and input pump energy of the pulsed Nd:YAG laser at 355 nm, are reported. Photon conversion
efficiencies of 50% and 27% are achieved at the first Stokes lines (S1) in H2 and D2, respectively. As a result, ultraviolet and visible laser light (274–503 nm) was generated with energies ranging from a few
mJ up to several tens of mJ.
Received: 5 January 1998/Revised version: 3 June 1998 相似文献
13.
Thermal grating and broadband degenerate four-wave mixing spectroscopy of OH in high-pressure flames
H. Latzel A. Dreizler T. Dreier J. Heinze M. Dillmann W. Stricker G.M. Lloyd P. Ewart 《Applied physics. B, Lasers and optics》1998,67(5):667-673
2 ∑–X2Π(0,0) band of OH has been studied in premixed methane/air flames using a cw Ar+ laser probe. Measurements of flame temperature and pressure were derived from fits of theoretical simulations to the observed
time variation of signals over a pressure range of 10 to 40 bar and for different stoichiometry that were in agreement with
independent measurements using N2 CARS and predictions of a one-dimensional flame calculation. Broadband DFWM spectra in the same band of OH were observed
up to a pressure of 9 bar, above which signals were obtained only from scattering from thermal gratings.
Received: 10 November 1997/Revised version: 28 May 1998 相似文献
14.
Received: 13 July 1998 / Revised version: 8 October 1998 / Published online: 24 February 1999 相似文献
15.
High-efficiency frequency conversion in H2 of a nitrogen laser oscillator-amplifier system is described. The laser system provides about 1 MW output power with a very low intrinsic divergence. Up to 3 Stokes lines at 392, 468, and 581 nm and 3 Anti-Stokes at 296, 263, and 237 nm, respectively, have been observed at the output of the 60 cm long H2 Raman cell. Peak power values of 500, 300, and 70 kW have been measured for the first 3 Stokes, respectively, corresponding to a 56% pump energy conversion efficiency.A comparison between free and guided propagation (in a hollow dielectric waveguide) is also reported, for various values of the pump intrinsic divergence. 相似文献
16.
4 /N2/O2 flame to spectral simulations based on a two-level theory for stationary, saturable absorbers by Abrams et al. Temperatures
determined from least-squares fits of simulations to experimental spectra in the A2Σ+?X2Π+(0,0) band are compared to temperatures obtained from OH absorption spectroscopy and a radiation-corrected thermocouple. We
find that DFWM rotational temperatures derived from Q-branch spectra agree with thermocouple and are independent of pump laser
intensity for low to moderate saturation (I≈Isat). However, the temperatures are systematically low and depend on pump intensity if the analysis neglects saturation effects.
We demonstrate a method for obtaining an effective pump saturation intensity for use with the two-level model. This approach
for analyzing saturated DFWM line intensities differs from previous work in that the use of the theory of Abrams et al. rather
than a transition-dipole-moment power law allows treatment of a much wider range of saturation. Based on the observed signal-to-noise
ratio an NO detection sensitivity of 25 ppm is projected, limited by a DFWM background interference specific to hydrocarbon
flames.
Received: 15 September 1998 / Revised version: 18 November 1998 / Published online: 24 February 1999 相似文献
17.
S. Hayashi T. Suzuki T. Ichimura K. Tsukiyama 《Applied physics. B, Lasers and optics》1997,65(4-5):555-561
2 Σ+,H′2Π(v′=0)←X2Π(v′′=0) two-photon transition of NO, both near-infrared and vacuum ultraviolet radiation were emitted along the laser propagation
direction. The analyses of emission and excitation spectra revealed that the parametric four-wave mixing (PFWM) process coexisted
with amplified spontaneous emission. Polarization properties of the IR radiation are found to be dependent on the rotational
levels. Pressure and laser power behaviors of the generated waves were reported. The mechanism of PFWM was discussed in terms
of selection rules of the relevant ro-vibronic transitions.
Received: 19 September 1996/Revised version: 27 January 1997 相似文献
18.
An experimental investigation (including a comparison with a simple theoretical model) of the effect of buffer-gas composition, pressure and temperature on resonant Degenerate Four-Wave Mixing (DFWM) has been performed. The DFWM signal from NO in a quartz cell was measured and the effect of quenching as well as elastic (phase-changing) collisions was studied by varying the total and partial pressures of N2 and CO2 as buffer gases. It was found that the DFWM signal first slowly increased with buffer-gas pressure (up to 10 mbar) and then rapidly decreased. It was furthermore found that the DFWM signal was considerably less sensitive to quenching collisions as compared to Laser-Induced Fluorescence (LIF) (for laser intensities approximately equal to half the DFWM saturation intensity of the transition). On the other hand, while LIF is virtually insensitive to elastic collisions, DFWM displays a larger sensitivity to elastic collisions than to quenching collisions. The DFWM saturation intensity was found to increase with buffer-gas pressure (although slower than expected). When varying the temperature of the gas composition, it was found that the DFWM signal decreased markedly with increasing temperature. This decrease is too fast to be explained solely by a change in the population of the molecular state probed by the laser. 相似文献
19.
E. Konz R. Grzeszik G. Marowsky V. Akimov L. Rusin H.-G. Rubahn 《Applied physics. B, Lasers and optics》1997,64(5):613-618
3 PJ) oxygen atoms are detected in a high pressure surface wave discharge driven at 2.45 GHz via two-photon resonant degenerate
four-wave mixing spectroscopy (TP-DFWM) in the forward folded BOX configuration. The nonlinear optical signal provides a direct
measure of the relative oxygen atom concentration with high spatial resolution inside the discharge up to pressures of 1 bar
and without distortions due to linear absorption or saturation effects. The axial distribution of oxygen atom concentration
is observed to depend sensitively on total pressure and gas flux. For total gas pressures up to 600 mbar both in case of a
mixture of 10% O2/He and 10% O2/Ar the concentration of oxygen atoms increases linearly with pressure. At higher pressures an increase with larger slope
is observed for 10% O2/Ar, while the concentration remains constant for 10% O2/He. This is interpreted by an increase of the three-body recombination rate in O2/He mixtures.
Received: 26 July 1996/Revised version: 15 November 1996 相似文献
20.
Differential absorption spectra measurements of tetrahedral Co2+-doped LiGa5O8 have been made using a ps pump-probe technique. The stimulated emission from the 4T1(4P) level to the 4A2(4F) and 4T2(4F) states is observed to be overlapped by the excited-state absorption. The excited-state absorption is tentatively assigned
to transition from the 4T1(4P) level of the Co2+ ion to the conduction band of LiGa5O8. For Co2+:LiGa5O8, laser operation is expected to be possible in the vicinity of 720 nm and in the 860–970 nm spectral region.
Received: 5 June 1998 / Revised version: 20 October 1998 / Published online: 19 May 1999 相似文献