Victor Pavlov - Profile on Academia.edu (original) (raw)
Papers by Victor Pavlov
Giant quadratic magneto-optical Kerr effect in (Eu,Gd)O films for magnetic field sensing
Applied Materials Today
Physical Review B
The picosecond and subpicosecond dynamics of spins in intrinsic and n-doped GaAs is investigated ... more The picosecond and subpicosecond dynamics of spins in intrinsic and n-doped GaAs is investigated at room temperature using the time-resolved, pump and probe, photoinduced, near-resonant magneto-optical Kerr effect between 1.44 and 1.63 eV. Three components with different temporal and spectral behavior are distinguished in both Kerr rotation and ellipticity, and their origin is discussed in relation with theoretical predictions and simulations. Two contributions are attributed to the splitting of the spin sublevels. The first one, present only as long as pump and probe pulses coincide in time, is a coherent response accounted for in terms of the optical Stark effect, whereas the longer decay of the second one, up to 35 ps, is attributed to electron spin relaxation. The third component is assumed to arise from the difference in population of the photoexcited states and decays within a time smaller than the pulse duration, which is attributed to the energy relaxation of electrons towards the bottom of the conduction band through carrier-carrier and carrier-phonon scattering.
Physical Review B
A time-resolved, all-optical technique based on the photo-induced magneto-optical Kerr effect is ... more A time-resolved, all-optical technique based on the photo-induced magneto-optical Kerr effect is applied to the spectral study of the sub-picosecond, room temperature spin dynamics in CdTe between 1.44 and 1.63 eV. Two relaxation processes with respective decay times of up to 200 fs and 2.5 ps are distinguished. While the longer one is attributed to electron-spin relaxation, several processes such as the redistribution of electrons in the conduction band or exciton ionization near the band gap are believed to take place on the timescale of the faster one. A change of the spectral dependence of the Kerr effect from a paramagneticlike to a diamagneticlike regime during this faster relaxation is observed and discussed.
Optical second harmonic generation in centrosymmetric antiferromagnetic NiO
Optical second harmonic generation (SHG) in NiO in spectroscopy and topography experiments reveal... more Optical second harmonic generation (SHG) in NiO in spectroscopy and topography experiments reveals a pronounced signal below the Neel temperature which couples quadratically to the antiferromagnetic order parameter. The SH process originates in combined magnetic-dipole and electric-dipole transitions between the (3d)8 levels of the Ni2+ ion in the crystal field. It is greatly enhanced by being resonant both in the
Magnetic circular dichroism in YBa2Cu3O(7-delta) and estimation of the magnitude of nonmutual optical phenomena predicted by the anion model of high-temperature superconductors
Results of measurements of magnetic circular dichroism in YBa2Cu3O(7-delta) films in the visible ... more Results of measurements of magnetic circular dichroism in YBa2Cu3O(7-delta) films in the visible spectral region are reported. Based on the results obtained the nonmutual optical effects, predicted by the anion model of high-temperature superconductors, are estimated at 10 exp -8 - 10 exp -7. This explains the negative results obtained earlier (Spielman et al., 1990) in laser gyroscope experiments, since
Physical Review B, 2001
Nonlinear magneto-optical phenomena related to the process of second harmonic generation in aniso... more Nonlinear magneto-optical phenomena related to the process of second harmonic generation in anisotropic films of different classes of symmetry are discussed. In the electric-dipole approximation two kinds of nonlinearity of crystallographic and magnetic origin may coexist in noncentrosymmetric crystals. The interference between the corresponding nonlinear optical waves results in novel magneto-optical effects, such as a transversal effect linear in magnetization at normal incidence and a circular magnetic asymmetry with no equivalence between light helicity and magnetization direction change. Epitaxial films of magnetic garnets grown on substrates with different crystallographic orientations were taken as a model anisotropic system for experimental studies. The unambiguous separation of the crystallographic and magnetic contributions to the second harmonic generation is demonstrated with the help of rotational anisotropy experiments. A theoretical model for the nonlinear light propagation in noncentrosymmetric magnetic films is developed. Calculations based on this model are found to be in good agreement with the experimental results.
Interface Sensitivity of Magneto-Optical Second Harmonic Generation from Ultrathin Cobalt Films
CLEO/Europe Conference on Lasers and Electro-Optics, 1998
ABSTRACT Not Available
Femtosecond Photo-Induced Phenomena in Multiferroic Hexagonal Manganite YMnO3
Solid State Phenomena, 2015
Transient optical anisotropy in the hexagonal manganite YMnO3 excited by linearly and circularly ... more Transient optical anisotropy in the hexagonal manganite YMnO3 excited by linearly and circularly polarized laser pulses has been observed. The photo-induced anisotropy was investigated by the pump-probe technique based on a femtosecond Ti:sapphire laser generating optical pulses at the photon energy of 1.55 eV. Temporal and spectral dependencies of the photo-induced optical rotation and ellipticity were analyzed by a theoretical model considering ultrafast population and relaxation processes near the interband transitions from the hybridized O2−(2p)-Mn3+(3d) (Γ1) to the Mn3+(3d3z2−r2) (Γ5) states at photon energies of the laser excitation. Very short relaxation time of ~10 fs, which is the Raman coherence time between the excited Γ5|x> and Γ5|y> states, has been determined. It is found that this coherence time is much shorter than a charge relaxation time of ~500 fs between the Γ5|x,y> and Γ1|g> states for the interband electronic transition Γ1→Γ5.
ICONO 2007: Coherent and Nonlinear Optical Phenomena, 2007
Spatial dispersion phenomena in magneto-optics
Physics of the Solid State, 1998
An experimental study of nonreciprocal spatial-dispersion effects in para-(Cd1−x MnxTe), ferro-(L... more An experimental study of nonreciprocal spatial-dispersion effects in para-(Cd1−x MnxTe), ferro-(LiFe5O8), and antiferromagnetic (Cr2O3) crystals caused by an external magnetic field or magnetic order is reported.
Nonlinear Optical Spectroscopy of the Two-Order-Parameter Compound YMnO3
Physical Review Letters, 1998
ABSTRACT We have observed two types of optical second harmonic spectra of Mn3+ ions in hexagonal ... more ABSTRACT We have observed two types of optical second harmonic spectra of Mn3+ ions in hexagonal YMnO3, one of which is caused by the noncentrosymmetric ferroelectric ordering of charges, whereas the other is due to the centrosymmetric antiferromagnetic ordering of spins. Partial overlapping between the electronic transitions gives rise to a new kind of nonlinear optical polarization P\(2omega\) = PFE\(2omega\)+PAFM\(2omega\), which depends on two order parameters. The magnitude and phase of P\(2omega\) can be changed by varying the ratio between the two contributions, as demonstrated by changing the contrast between 180° antiferromagnetic domains, which are indistinguishable in linear optics.
Magnetoelectric Spectroscopy of Electronic Transitions in Antiferromagnetic Cr2O3
Physical Review Letters, 1996
ABSTRACT Optical effects due to electric dipole–magnetic dipole interference were predicted for c... more ABSTRACT Optical effects due to electric dipole–magnetic dipole interference were predicted for crystals which are noninvariant under space-inversion and time-reversal symmetry. We report measurements of the nonreciprocal rotation and ellipticity of light reflected from antiferromagnetic-magnetoelectric Cr2O3 in a spectral range from 1.6 to 2.5 eV, which comprises 4A2→2E, 2T1, and 4T2 transitions. An analysis provides new information about symmetries of excited states and shows that previous assignments of excitonic lines cannot be entirely reconciled with our data.
Ultrafast Optical Pumping of Spin and Orbital Polarizations in the Antiferromagnetic Mott Insulators R2CuO4
Physical Review Letters, 2007
We demonstrate that optical pumping by circularly polarized light at the charge-transfer transiti... more We demonstrate that optical pumping by circularly polarized light at the charge-transfer transition can induce spin and orbital polarizations in the strongly correlated Mott insulators R(2)CuO(4) (R=Pr, Nd, Sm) providing a means of ultrafast nonlinear manipulation of spin states on time scales of less than 150 fs. We propose a model which includes both orbital- and spin-related processes possessing different spectral and temporal properties. This allows us to model the optical response of antiferromagnetic Mott insulators to circularly polarized light and estimate the spin relaxation time as tau(s) approximately 30-50 fs.
Magneto-Stark Effect of Excitons as the Origin of Second Harmonic Generation in ZnO
Physical Review Letters, 2013
The magneto-Stark effect of excitons is demonstrated to be an efficient source of optical nonline... more The magneto-Stark effect of excitons is demonstrated to be an efficient source of optical nonlinearity in hexagonal ZnO. Strong resonant second harmonic generation signals induced by an external magnetic field are observed in the spectral range of 2s and 2p excitons. The microscopic theoretical analysis shows that for excitons with a finite wave vector, exciton states of opposite parity are mixed by an effective odd parity electric field induced by the magnetic field despite its even parity. The field, spectral, and polarization dependencies of the second harmonic generation intensity validate the proposed mechanism. The observed phenomenon is not limited to a certain symmetry class and therefore must be effective in other semiconductors.
Determination of the Magnetic Symmetry of Hexagonal Manganites by Second Harmonic Generation
Physical Review Letters, 2000
Optical second harmonic spectroscopy is introduced as a powerful supplement for the determination... more Optical second harmonic spectroscopy is introduced as a powerful supplement for the determination of complex magnetic structures. Experimental efforts are simplified and new degrees of freedom are opened. Thereby, some principal or technical restrictions of neutron or magnetic x-ray diffraction experiments are overcome. High spatial resolution leads to additional information about magnetically ordered matter. As an example, the noncollinear magnetic structure of the hexagonal manganites RMnO3 ( R = Sc, Y, Ho, Er, Tm, Yb, Lu) is analyzed. The results show that some earlier conclusions on their magnetic symmetry and properties should be revised.
Spin and Orbital Quantization of Electronic States as Origins of Second Harmonic Generation in Semiconductors
Physical Review Letters, 2006
Basically different mechanisms of optical second harmonic generation (SHG) in semiconductors, ind... more Basically different mechanisms of optical second harmonic generation (SHG) in semiconductors, induced by an external magnetic field H, have been identified experimentally by studying the diluted magnetic semiconductor (Cd,Mn)Te. For paramagnetic (Cd,Mn)Te the SHG response is governed by spin quantization of electronic states, in contrast with diamagnetic CdTe with its dominating orbital quantization. The mechanisms can be identified by the distinct magnetic field dependence of the SHG intensity which scales with the spin splitting in the paramagnetic case as compared to the H2 dependence observed for the diamagnetic case.
Orbital quantization of electronic states in a magnetic field as the origin of second-harmonic generation in diamagnetic semiconductors
Physical Review B, 2006
ABSTRACT Magnetic-field-induced second-harmonic generation (MFISH) has been studied in the III-V ... more ABSTRACT Magnetic-field-induced second-harmonic generation (MFISH) has been studied in the III-V and II-VI diamagnetic semiconductors GaAs, CdTe, and (Cd,Mg)Te over broad spectral ranges and at temperatures varying from 6 to 200 K. The external magnetic field gives rise to time-reversal symmetry breaking, causing optical nonlinearities. A series of narrow MFISH lines has been observed in the spectral range near the band gap in magnetic fields up to 11 T. The magnetoexciton states associated with the optical transitions between Landau levels are responsible for the observed MFISH spectra. Orbital quantization of electronic states is therefore established as an origin of MFISH generation. The rotational anisotropy of the MFISH signal distinctly differs from that in the electric-dipole approximation. Model calculations, based on a phenomenological analysis using nonlocal contributions to the nonlinear optical susceptibility, reveal the importance of nonlinear magneto-optical spatial-dispersion, which acts together with the electric-dipole term.
Physical Review B, 2010
EuTe possesses the centrosymmetric crystal structure m3m of rocksalt type in which the second-har... more EuTe possesses the centrosymmetric crystal structure m3m of rocksalt type in which the second-harmonic generation is forbidden in electric dipole approximation but the third-harmonic generation ͑THG͒ is allowed. We studied the THG spectra of this material and observed several resonances in the vicinity of the band gap at 2.2-2.5 eV and at higher energies up to 4 eV, which are related to four-photon THG processes. The observed resonances are assigned to specific combinations of electronic transitions between the ground 4f 7 state at the top of the valence band and excited 4f 6 5d 1 states of Eu 2+ ions, which form the lowest energy conduction band. Temperature, magnetic field, and rotational anisotropy studies allowed us to distinguish crystallographic and magnetic-field-induced contributions to the THG. A strong modification of THG intensity for the 2.4 eV band and suppression of the THG for the 3.15 eV band was observed in applied magnetic field. Two main features of the THG spectra were assigned to 5d͑t 2g ͒ and 5d͑e g ͒ subbands at 2.4 eV and 3.15 eV, respectively. A microscopic quantum-mechanical model of the THG response was developed and its conclusions are in qualitative agreement with the experimental results.
Giant quadratic magneto-optical Kerr effect in (Eu,Gd)O films for magnetic field sensing
Applied Materials Today
Physical Review B
The picosecond and subpicosecond dynamics of spins in intrinsic and n-doped GaAs is investigated ... more The picosecond and subpicosecond dynamics of spins in intrinsic and n-doped GaAs is investigated at room temperature using the time-resolved, pump and probe, photoinduced, near-resonant magneto-optical Kerr effect between 1.44 and 1.63 eV. Three components with different temporal and spectral behavior are distinguished in both Kerr rotation and ellipticity, and their origin is discussed in relation with theoretical predictions and simulations. Two contributions are attributed to the splitting of the spin sublevels. The first one, present only as long as pump and probe pulses coincide in time, is a coherent response accounted for in terms of the optical Stark effect, whereas the longer decay of the second one, up to 35 ps, is attributed to electron spin relaxation. The third component is assumed to arise from the difference in population of the photoexcited states and decays within a time smaller than the pulse duration, which is attributed to the energy relaxation of electrons towards the bottom of the conduction band through carrier-carrier and carrier-phonon scattering.
Physical Review B
A time-resolved, all-optical technique based on the photo-induced magneto-optical Kerr effect is ... more A time-resolved, all-optical technique based on the photo-induced magneto-optical Kerr effect is applied to the spectral study of the sub-picosecond, room temperature spin dynamics in CdTe between 1.44 and 1.63 eV. Two relaxation processes with respective decay times of up to 200 fs and 2.5 ps are distinguished. While the longer one is attributed to electron-spin relaxation, several processes such as the redistribution of electrons in the conduction band or exciton ionization near the band gap are believed to take place on the timescale of the faster one. A change of the spectral dependence of the Kerr effect from a paramagneticlike to a diamagneticlike regime during this faster relaxation is observed and discussed.
Optical second harmonic generation in centrosymmetric antiferromagnetic NiO
Optical second harmonic generation (SHG) in NiO in spectroscopy and topography experiments reveal... more Optical second harmonic generation (SHG) in NiO in spectroscopy and topography experiments reveals a pronounced signal below the Neel temperature which couples quadratically to the antiferromagnetic order parameter. The SH process originates in combined magnetic-dipole and electric-dipole transitions between the (3d)8 levels of the Ni2+ ion in the crystal field. It is greatly enhanced by being resonant both in the
Magnetic circular dichroism in YBa2Cu3O(7-delta) and estimation of the magnitude of nonmutual optical phenomena predicted by the anion model of high-temperature superconductors
Results of measurements of magnetic circular dichroism in YBa2Cu3O(7-delta) films in the visible ... more Results of measurements of magnetic circular dichroism in YBa2Cu3O(7-delta) films in the visible spectral region are reported. Based on the results obtained the nonmutual optical effects, predicted by the anion model of high-temperature superconductors, are estimated at 10 exp -8 - 10 exp -7. This explains the negative results obtained earlier (Spielman et al., 1990) in laser gyroscope experiments, since
Physical Review B, 2001
Nonlinear magneto-optical phenomena related to the process of second harmonic generation in aniso... more Nonlinear magneto-optical phenomena related to the process of second harmonic generation in anisotropic films of different classes of symmetry are discussed. In the electric-dipole approximation two kinds of nonlinearity of crystallographic and magnetic origin may coexist in noncentrosymmetric crystals. The interference between the corresponding nonlinear optical waves results in novel magneto-optical effects, such as a transversal effect linear in magnetization at normal incidence and a circular magnetic asymmetry with no equivalence between light helicity and magnetization direction change. Epitaxial films of magnetic garnets grown on substrates with different crystallographic orientations were taken as a model anisotropic system for experimental studies. The unambiguous separation of the crystallographic and magnetic contributions to the second harmonic generation is demonstrated with the help of rotational anisotropy experiments. A theoretical model for the nonlinear light propagation in noncentrosymmetric magnetic films is developed. Calculations based on this model are found to be in good agreement with the experimental results.
Interface Sensitivity of Magneto-Optical Second Harmonic Generation from Ultrathin Cobalt Films
CLEO/Europe Conference on Lasers and Electro-Optics, 1998
ABSTRACT Not Available
Femtosecond Photo-Induced Phenomena in Multiferroic Hexagonal Manganite YMnO3
Solid State Phenomena, 2015
Transient optical anisotropy in the hexagonal manganite YMnO3 excited by linearly and circularly ... more Transient optical anisotropy in the hexagonal manganite YMnO3 excited by linearly and circularly polarized laser pulses has been observed. The photo-induced anisotropy was investigated by the pump-probe technique based on a femtosecond Ti:sapphire laser generating optical pulses at the photon energy of 1.55 eV. Temporal and spectral dependencies of the photo-induced optical rotation and ellipticity were analyzed by a theoretical model considering ultrafast population and relaxation processes near the interband transitions from the hybridized O2−(2p)-Mn3+(3d) (Γ1) to the Mn3+(3d3z2−r2) (Γ5) states at photon energies of the laser excitation. Very short relaxation time of ~10 fs, which is the Raman coherence time between the excited Γ5|x> and Γ5|y> states, has been determined. It is found that this coherence time is much shorter than a charge relaxation time of ~500 fs between the Γ5|x,y> and Γ1|g> states for the interband electronic transition Γ1→Γ5.
ICONO 2007: Coherent and Nonlinear Optical Phenomena, 2007
Spatial dispersion phenomena in magneto-optics
Physics of the Solid State, 1998
An experimental study of nonreciprocal spatial-dispersion effects in para-(Cd1−x MnxTe), ferro-(L... more An experimental study of nonreciprocal spatial-dispersion effects in para-(Cd1−x MnxTe), ferro-(LiFe5O8), and antiferromagnetic (Cr2O3) crystals caused by an external magnetic field or magnetic order is reported.
Nonlinear Optical Spectroscopy of the Two-Order-Parameter Compound YMnO3
Physical Review Letters, 1998
ABSTRACT We have observed two types of optical second harmonic spectra of Mn3+ ions in hexagonal ... more ABSTRACT We have observed two types of optical second harmonic spectra of Mn3+ ions in hexagonal YMnO3, one of which is caused by the noncentrosymmetric ferroelectric ordering of charges, whereas the other is due to the centrosymmetric antiferromagnetic ordering of spins. Partial overlapping between the electronic transitions gives rise to a new kind of nonlinear optical polarization P\(2omega\) = PFE\(2omega\)+PAFM\(2omega\), which depends on two order parameters. The magnitude and phase of P\(2omega\) can be changed by varying the ratio between the two contributions, as demonstrated by changing the contrast between 180° antiferromagnetic domains, which are indistinguishable in linear optics.
Magnetoelectric Spectroscopy of Electronic Transitions in Antiferromagnetic Cr2O3
Physical Review Letters, 1996
ABSTRACT Optical effects due to electric dipole–magnetic dipole interference were predicted for c... more ABSTRACT Optical effects due to electric dipole–magnetic dipole interference were predicted for crystals which are noninvariant under space-inversion and time-reversal symmetry. We report measurements of the nonreciprocal rotation and ellipticity of light reflected from antiferromagnetic-magnetoelectric Cr2O3 in a spectral range from 1.6 to 2.5 eV, which comprises 4A2→2E, 2T1, and 4T2 transitions. An analysis provides new information about symmetries of excited states and shows that previous assignments of excitonic lines cannot be entirely reconciled with our data.
Ultrafast Optical Pumping of Spin and Orbital Polarizations in the Antiferromagnetic Mott Insulators R2CuO4
Physical Review Letters, 2007
We demonstrate that optical pumping by circularly polarized light at the charge-transfer transiti... more We demonstrate that optical pumping by circularly polarized light at the charge-transfer transition can induce spin and orbital polarizations in the strongly correlated Mott insulators R(2)CuO(4) (R=Pr, Nd, Sm) providing a means of ultrafast nonlinear manipulation of spin states on time scales of less than 150 fs. We propose a model which includes both orbital- and spin-related processes possessing different spectral and temporal properties. This allows us to model the optical response of antiferromagnetic Mott insulators to circularly polarized light and estimate the spin relaxation time as tau(s) approximately 30-50 fs.
Magneto-Stark Effect of Excitons as the Origin of Second Harmonic Generation in ZnO
Physical Review Letters, 2013
The magneto-Stark effect of excitons is demonstrated to be an efficient source of optical nonline... more The magneto-Stark effect of excitons is demonstrated to be an efficient source of optical nonlinearity in hexagonal ZnO. Strong resonant second harmonic generation signals induced by an external magnetic field are observed in the spectral range of 2s and 2p excitons. The microscopic theoretical analysis shows that for excitons with a finite wave vector, exciton states of opposite parity are mixed by an effective odd parity electric field induced by the magnetic field despite its even parity. The field, spectral, and polarization dependencies of the second harmonic generation intensity validate the proposed mechanism. The observed phenomenon is not limited to a certain symmetry class and therefore must be effective in other semiconductors.
Determination of the Magnetic Symmetry of Hexagonal Manganites by Second Harmonic Generation
Physical Review Letters, 2000
Optical second harmonic spectroscopy is introduced as a powerful supplement for the determination... more Optical second harmonic spectroscopy is introduced as a powerful supplement for the determination of complex magnetic structures. Experimental efforts are simplified and new degrees of freedom are opened. Thereby, some principal or technical restrictions of neutron or magnetic x-ray diffraction experiments are overcome. High spatial resolution leads to additional information about magnetically ordered matter. As an example, the noncollinear magnetic structure of the hexagonal manganites RMnO3 ( R = Sc, Y, Ho, Er, Tm, Yb, Lu) is analyzed. The results show that some earlier conclusions on their magnetic symmetry and properties should be revised.
Spin and Orbital Quantization of Electronic States as Origins of Second Harmonic Generation in Semiconductors
Physical Review Letters, 2006
Basically different mechanisms of optical second harmonic generation (SHG) in semiconductors, ind... more Basically different mechanisms of optical second harmonic generation (SHG) in semiconductors, induced by an external magnetic field H, have been identified experimentally by studying the diluted magnetic semiconductor (Cd,Mn)Te. For paramagnetic (Cd,Mn)Te the SHG response is governed by spin quantization of electronic states, in contrast with diamagnetic CdTe with its dominating orbital quantization. The mechanisms can be identified by the distinct magnetic field dependence of the SHG intensity which scales with the spin splitting in the paramagnetic case as compared to the H2 dependence observed for the diamagnetic case.
Orbital quantization of electronic states in a magnetic field as the origin of second-harmonic generation in diamagnetic semiconductors
Physical Review B, 2006
ABSTRACT Magnetic-field-induced second-harmonic generation (MFISH) has been studied in the III-V ... more ABSTRACT Magnetic-field-induced second-harmonic generation (MFISH) has been studied in the III-V and II-VI diamagnetic semiconductors GaAs, CdTe, and (Cd,Mg)Te over broad spectral ranges and at temperatures varying from 6 to 200 K. The external magnetic field gives rise to time-reversal symmetry breaking, causing optical nonlinearities. A series of narrow MFISH lines has been observed in the spectral range near the band gap in magnetic fields up to 11 T. The magnetoexciton states associated with the optical transitions between Landau levels are responsible for the observed MFISH spectra. Orbital quantization of electronic states is therefore established as an origin of MFISH generation. The rotational anisotropy of the MFISH signal distinctly differs from that in the electric-dipole approximation. Model calculations, based on a phenomenological analysis using nonlocal contributions to the nonlinear optical susceptibility, reveal the importance of nonlinear magneto-optical spatial-dispersion, which acts together with the electric-dipole term.
Physical Review B, 2010
EuTe possesses the centrosymmetric crystal structure m3m of rocksalt type in which the second-har... more EuTe possesses the centrosymmetric crystal structure m3m of rocksalt type in which the second-harmonic generation is forbidden in electric dipole approximation but the third-harmonic generation ͑THG͒ is allowed. We studied the THG spectra of this material and observed several resonances in the vicinity of the band gap at 2.2-2.5 eV and at higher energies up to 4 eV, which are related to four-photon THG processes. The observed resonances are assigned to specific combinations of electronic transitions between the ground 4f 7 state at the top of the valence band and excited 4f 6 5d 1 states of Eu 2+ ions, which form the lowest energy conduction band. Temperature, magnetic field, and rotational anisotropy studies allowed us to distinguish crystallographic and magnetic-field-induced contributions to the THG. A strong modification of THG intensity for the 2.4 eV band and suppression of the THG for the 3.15 eV band was observed in applied magnetic field. Two main features of the THG spectra were assigned to 5d͑t 2g ͒ and 5d͑e g ͒ subbands at 2.4 eV and 3.15 eV, respectively. A microscopic quantum-mechanical model of the THG response was developed and its conclusions are in qualitative agreement with the experimental results.