KEYWORDS: Phase conjugation, Four wave mixing, Signal attenuation, Nonlinear optics, Signal processing, Information technology, Scattering, Optical amplifiers, Image registration, Signal detection
For the phase conjugated wave at four-wave mixing at SBS the transient analytical solution is obtained. A rate of the
reflected wave amplitude increasing and a range of values of coupled waves parameters in which time instability is most
essential are determined. Conditions of attenuation of absolute instability influence on considered process of phase
conjugation are noted.
The geometry of Raman shifter with self-intersection of pumping beam is proposed. The generation of a Stokes wave
takes place in a separate ring resonator with a non-linear parametric mirror. The spatial location of a ring resonator with
respect to pumping waves has determined. For this geometry conditions of the phase matching and effective interaction
of waves at different frequency mixing are realized. The scheme allows to essentially expand spectral range of SRS
converters.
We present a systematic study of the birefringence (including Sellmeier equations valid in the 0.6-11.5 μm range) and
nonlinearity of the orthorhombic AgGaGenSe2(n+1) crystals for n=2...5, solid solutions in the system AgGaSe2-nGeSe2.
The birefringence, e.g. na-nc at 1064.2 nm, increases from 0.114 for n=2 (AgGaGe2Se6) to 0.149 for n=5 (AgGaGe5Se12)
which substantially exceeds the birefringence of the uniaxial AgGaSe2 (~0.022), the parent compound in the limit n=0.
All four quaternary compounds are optically negative biaxial crystals. The calculated SHG limit (minimum fundamental
wavelength) is ≈1470 nm for AgGaGe2Se6 and ≈1240 nm for AgGaGe5Se12, for type-I interaction and propagation along
the Y principal optical axis. These limits are much lower than the ≈3120 nm limit for type-I interaction in AgGaSe2.
Thus, the AgGaGenSe2(n+1) crystals can be used for SHG down to their band-edge. The results for the nonlinear
coefficients of AgGaGenSe2(n+1) (n=3, 4 and 5), obtained from phase-matched SHG, indicate weak dependence on the
composition. On the average, the larger nonlinear coefficient d31 is very close to d36 of AgGaSe2 (~30 pm/V) while d32 is roughly two times smaller.
In the report questions of influence of broadbandness and structure of a spectrum of pumping radiation on optical parametric oscillator efficiency are considered. The results of experiment are in accordance with conclusions of the theoretical analysis and estimations.
The quantitative estimation of influence of coherence length of pumping radiation on amplification of a signal wave in the optical parametric oscillator is made. It is shown, that the decreasing of coherence length can result in to a decrease of amplification and stability of the oscillator parameters. Especially noticeably these factors can become apparent, when the coherence length of pumping radiation is less than waves interaction length in a non-linear crystal.
Experimental researches of parameters of self-starting Nd:YAG laser with electroptic shutter are carried out and the application opportunity of this laser for pump of the optical parametrical oscillator is analysed. It is shown, that it is important to use spatial and frequency selection in the self-starting laser.
It is theoretically shown, that the Brillouin laser of the conjugated wave allows expanding abilities of PC at SBS for excimer lasers broadband radiation. The optical arrangements and nonlinear media for PC at SBS with a feedback of excimer lasers radiation are offered.
It is shown theoretically, that the axial modes of radiation in PC mirrors at four-wave mixing with a feedback without selection in the resonator result to generation of a direct wave and suppress generation of a backward wave with the conjugated wave front. It is established, that due to axial modes in self-starting lasers the holographic feedback is carrying out the function of the output mirror of the resonator forms. The large role of polarization discrimination at Faraday effect in PC mirrors at four-wave mixing with a feedback and in self-adaptive lasers is marked.
It is shown theoretically, that observed in experiments the strong low threshold feedback in the resonator with a high pressure gas (Xe) cell of the CO2 laser, in which the frequency interval between axial modes is equal to frequency Stokes shift at Stimulated Brillouin Scattering (SBS) in Xe, can arise owing to nondegenerate four-wave mixing in a gas cell on generated as at SBS running phase gratings.
A wide range of physical properties of mercury thiogallate crystals is studied for development and optimization of OPO based on these crystals. The obtained results provide to conclude that OPO on HgGa2S4 crystals can occupy one of the leading positions among the analogous devices in the mid-infrared region.
The theoretical investigation and numerical simulation of phase conjugation (PC) at stimulated Brillouin scattering (SBS) with feedback is carried out. A case of long pulse PC is considered. At this condition both running and standing phase gratings which responsible for the positive feedback are taken to account. The threshold of PC wave generation and PC reflectivity are calculated. The numerical solution for temporal behavior of PC intensity is obtained.
A temporal behavior of a phase conjugation reflectivity R at degenerate four-wave mixing (DFWM) in InSb for a pulsed carbon-dioxide laser radiation is theoretically investigated. It is shown, that R at a transient DFWM is determined by a response time of a nonlinear medium, which depends on intensity of a radiation, and can be some times higher than a reflectivity for non-transient condition.
Degenerate four-wave mixing (DFWM) and phase conjugation (PC) of pulsed carbon-dioxide laser radiation on transient gratings inside its own laser medium have been studied both experimentally and theoretically. The operational mode of the e-beam controlled discharge carbon-dioxide laser has been chosen in such a way (CO2:N2:He equals 1:2:4, p equals 0.28 atm, tin equals 30 microseconds) that the laser pulse length (tauout approximately 10 - 20 microseconds) is comparable with an effective relaxation time of the upper laser level (taurel approximately 15 - 30 microseconds). The time-history of the carbon-dioxide laser and pc signal pulses, and pc reflectivity have been thoroughly investigated for different cavity Q factors and specific electrical energy inputs. It has been shown, that the formation of the PC signal under the intracavity DFWM on gain (amplitude) and thermal (phase) gratings is characterized by a complicated time history that reflects the main relaxation processes taking place inside the inverted medium. A feature of the transient pc process inside the laser active medium is the dependence of the effective relaxation time of the upper laser level on the intensity of pumping waves. Pc reflectivity has been obtained by numerical calculations. A comparison of the theoretical and experimental data confirms the contribution of two different mechanisms of grating formation under DFWM inside the active medium of the carbon-dioxide laser.
Degenerate four-wave mixing (DFWM) and phase conjugation (PC) of pulsed carbon-dioxide laser radiation on transient gratings inside its own laser medium have been studied both experimentally and theoretically. The operational mode of the e-beam controlled discharge carbon-dioxide laser has been chosen in such a way (CO2:N2:He equals 1:2:4, p equals 0.28 atm, tin equals 30 microseconds) that the laser pulse length ((tau) out approximately equals 10 - 20 microseconds) is comparable with an effective relaxation time of the upper laser level ((tau) rel approximately 15 - 30 microseconds). The time-history of the carbon-dioxide laser and PC signal pulses, and PC reflectivity have been thoroughly investigated for different cavity Q factors and specific electrical energy inputs. It has been shown, that the formation of the PC signal under the intracavity DFWM on gain (amplitude) and thermal (phase) gratings is characterized by a complicated time history that reflects the main relaxation processes taking place inside the inverted medium. A feature of the transient PC process inside the laser active medium is the dependence of the effective relaxation time of the upper laser level on the intensity of pumping waves. PC reflectivity has been obtained by numerical calculations. A comparison of the theoretical and experimental data confirms the contribution of two different mechanisms of grating formation under DFWM inside the active medium of the carbon-dioxide laser.
The reflectivity of UV-laser beams under degenerate four-wave mixing in solid-state and liquid media is calculated in the case of electrostriction nonlinearity. It is shown that the response time of DFWM is quite short and its efficiency is high in comparison with SBS. We believe that such DFWM-mirrors can be efficiently used as PC-mirrors in UV. In theory the possibilities of a nonlinearity electrostriction mechanism for degenerate four-wave mixing (DFWM) of excimer lasers radiation have been analyzed. It should be noted that these lasers require a high speed response of a nonlinear medium. The dynamic fine (small) scale grating providing phase conjugation (PC) of pulse excimer lasers with a reflection coefficient by several tens of percentage has been demonstrated to have little response time (less than 10-9 s).
Degenerate four-wave mixing (DFWM) and phase conjugation (PC) of pulsed CO2 laser radiation on transient gratings inside its own laser medium have been studied both experimentally and theoretically. The operational mode of the e-beam controlled discharge CO2 laser has been chosen in such a way (CO2:N2:He equals 1:2:4, p equals 0.28 atm, tin equals 30 microsecond(s) ) that the laser pulse length ((tau) out approximately 10 - 20 microsecond(s) ) is comparable with an effective relaxation time of the upper laser level ((tau) rel approximately 15 - 30 microsecond(s) ). The time-history of the CO2 laser and PC signal pulses, and PC reflectivity have been thoroughly investigated for different cavity Q factors and specific electrical energy inputs. It has been shown, that the formation of the PC signal under the intracavity DFWM on gain (amplitude) and thermal (phase) gratings is characterized by a complicated time history that reflects the main relaxation processes taking place inside the inverted medium. A feature of the transient PC process inside the laser active medium is the dependence of the effective relaxation time of the upper laser level on the intensity of pumping waves. PC reflectivity has been obtained by numerical calculations. A comparison of the theoretical and experimental data confirms the contribution of two different mechanisms of grating formation under DFWM inside the active medium of the CO2 laser.
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