Three methods are of great importance for super-high resolution spectroscopy and in obtaining supernarrow resonances. These are as follows: the method of saturated absorption, two-photon spectroscopy, and the method of separated optical fields. The first two methods are well known and developed. Recent progress in developing these methods has been discussed in [1]. The narrowest resonances and high resolution were obtained by the method of saturated absorption. It is based on the use of a Lamb dip [2] in an absorption line. The use of absorption saturation resonances has been begun in 1967 with investigations of He-Ne lasers with a Ne absorbent which were independently carried out in Perkin Elmer laboratories [3] and in our institute [4].Three methods are of great importance for super-high resolution spectroscopy and in obtaining supernarrow resonances. These are as follows: the method of saturated absorption, two-photon spectroscopy, and the method of separated optical fields. The first two methods are well known and developed. Recent progress in developing these methods has been discussed in [1]. The narrowest resonances and high resolution were obtained by the method of saturated absorption. It is based on the use of a Lamb dip [2] in an absorption line. The use of absorption saturation resonances has been begun in 1967 with investigations of He-Ne lasers with a Ne absorbent which were independently carried out in Perkin Elmer laboratories [3] and in our institute [4].

Soviet Journal of Quantum ElectronicsAug 31, 19782 citations

Theory of Two-Photon Absorption

Hiroshi Sekiya, Seikyo Tsunekawa, Kiyoshi Nishikawa +1 more

The science reports of the Kanazawa University＝金沢大学理科報告Jun 1, 19770 citations

Resonant enhancement of direct two-photon absorption in Tb3+ : LiYF4

Huang Jin, G. K. Liu, R. L. Cone

Resonant enhancement by a factor of over 20 of direct two-photon absorption from the ground state $^{7}\mathrm{F}_{6}$ to the excited state $^{5}\mathrm{G}_{6}$ of the 4 ${f}^{8}$ configuration of the ${\mathrm{Tb}}^{3+}$ ion at 40 200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ has been observed in time-resolved experiments with two separate pulsed lasers. The results provide clear evidence for resonant enhancement of two-photon absorption in rare-earth compounds and imply a similar enhancement for Raman scattering and nonlinear-optical mixing. Two separate contributions to the direct transition moment were observed. When a single laser frequency was used, the intermediate states which made the largest contribution were from excited configurations of opposite parity; those intermediate states were far from resonance. Detailed two-frequency experiments showed, however, that near a single photon $^{7}\mathrm{F}_{6}$ ${\mathrm{\ensuremath{-}}}^{5}$ ${\mathrm{D}}_{4}$ resonance, a much stronger contribution arose from the 4 ${f}^{8}$ configuration $^{5}\mathrm{D}_{4}$ intermediate state. Two-photon absorption was clearly isolated from two-step (incoherent) excitation by varying the timing of two separately triggered lasers.Resonant enhancement by a factor of over 20 of direct two-photon absorption from the ground state $^{7}\mathrm{F}_{6}$ to the excited state $^{5}\mathrm{G}_{6}$ of the 4${f}^{8}$ configuration of the ${\mathrm{Tb}}^{3+}$ ion at 40 200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ has been observed in time-resolved experiments with two separate pulsed lasers. The results provide clear evidence for resonant enhancement of two-photon absorption in rare-earth compounds and imply a similar enhancement for Raman scattering and nonlinear-optical mixing. Two separate contributions to the direct transition moment were observed. When a single laser frequency was used, the intermediate states which made the largest contribution were from excited configurations of opposite parity; those intermediate states were far from resonance. Detailed two-frequency experiments showed, however, that near a single photon $^{7}\mathrm{F}_{6}$${\mathrm{\ensuremath{-}}}^{5}$${\mathrm{D}}_{4}$ resonance, a much stronger contribution arose from the 4${f}^{8}$ configuration $^{5}\mathrm{D}_{4}$ intermediate state. Two-photon absorption was clearly isolated from two-step (incoherent) excitation by varying the timing of two separately triggered lasers.

Physical review. B, Condensed matterApr 1, 198920 citations

Multi-photon resonance phenomena using Laguerre–Gaussian beams

Seyedeh Hamideh Kazemi, Mohammad Mahmoudi

We study the influence of laser profile on the linewidth of the optical spectrum of multi-photon resonance phenomena. First, we investigate the dependence of the absorption spectrum on the laser profile in a two-level system. Thanks to the Laguerre–Gaussian field, the linewidth of the one-photon optical pumping and two-photon absorption peaks are explicitly narrower than that obtained with a Gaussian field. In the next section, it is shown that, compared to the Gaussian fields, the Laguerre–Gaussian ones reduce the linewidth of the optical spectrum in the coherent population trapping. Interestingly, it turns out that the use of a Laguerre–Gaussian beam makes the linewidth of the spectrum narrower as compared with a Gaussian one in Doppler-broadened electromagnetically induced transparency. Moreover, we study the effect of the laser profile on the Autler–Townes doublet structure in the absorption spectrum for a laser-driven four-level atomic system. We also consider the different values of the Laguerre–Gaussian mode beam waist, and, perhaps more remarkably, we find that for the small waist values, the Autler–Townes doublet can be removed and a prominent narrow central peak appears in the absorption spectrum. Finally, we investigate the effect of the laser profile on the linewidth of the sub-natural three-photon absorption peak of double dark resonance. The differences in the linewidth are quite large, offering potential applications in metrology and isotope separation methods. Our results can be used for super ultra-high resolution laser spectroscopy and to improve the resolution of the technology of isotope/isomer separation and photo-biology even at essential overlap of the spectra of the different particles.We study the influence of laser profile on the linewidth of the optical spectrum of multi-photon resonance phenomena. First, we investigate the dependence of the absorption spectrum on the laser profile in a two-level system. Thanks to the Laguerre–Gaussian field, the linewidth of the one-photon optical pumping and two-photon absorption peaks are explicitly narrower than that obtained with a Gaussian field. In the next section, it is shown that, compared to the Gaussian fields, the Laguerre–Gaussian ones reduce the linewidth of the optical spectrum in the coherent population trapping. Interestingly, it turns out that the use of a Laguerre–Gaussian beam makes the linewidth of the spectrum narrower as compared with a Gaussian one in Doppler-broadened electromagnetically induced transparency. Moreover, we study the effect of the laser profile on the Autler–Townes doublet structure in the absorption spectrum for a laser-driven four-level atomic system. We also consider the different values of the Laguerre–Gaussian mode beam waist, and, perhaps more remarkably, we find that for the small waist values, the Autler–Townes doublet can be removed and a prominent narrow central peak appears in the absorption spectrum. Finally, we investigate the effect of the laser profile on the linewidth of the sub-natural three-photon absorption peak of double dark resonance. The differences in the linewidth are quite large, offering potential applications in metrology and isotope separation methods. Our results can be used for super ultra-high resolution laser spectroscopy and to improve the resolution of the technology of isotope/isomer separation and photo-biology even at essential overlap of the spectra of the different particles.

arXiv:1607.08281Journal of Physics B Atomic Molecular and Optical PhysicsNov 22, 201613 citations

Theory of Two-Photon Absorption

清西川, 昭佐道, Hiroshi Sekiya +3 more

Jun 1, 19770 citations

Resonant enhancement by a factor of over 20 of direct two-photon absorption from the ground state

^{7}\mathrm{F}_{6}

to the excited state

^{5}\mathrm{G}_{6}

of the 4

{f}^{8}

configuration of the

{\mathrm{Tb}}^{3+}

ion at 40 200 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ has been observed in time-resolved experiments with two separate pulsed lasers. The results provide clear evidence for resonant enhancement of two-photon absorption in rare-earth compounds and imply a similar enhancement for Raman scattering and nonlinear-optical mixing. Two separate contributions to the direct transition moment were observed. When a single laser frequency was used, the intermediate states which made the largest contribution were from excited configurations of opposite parity; those intermediate states were far from resonance. Detailed two-frequency experiments showed, however, that near a single photon

^{7}\mathrm{F}_{6}

${\mathrm{\ensuremath{-}}}^{5}$

{\mathrm{D}}_{4}

resonance, a much stronger contribution arose from the 4

{f}^{8}

configuration

^{5}\mathrm{D}_{4}

intermediate state. Two-photon absorption was clearly isolated from two-step (incoherent) excitation by varying the timing of two separately triggered lasers.