Physical Review Letters

Excitation, Relaxation, and Continuous Maser Action in the 2.613-Micron Transition of Ca F2 : U3+

Gary D. Boyd, R. J. Collins, Sergio P. S. Porto, Avigail Yariv, W. A. Hargreaves

Published Apr 1, 1962• 80 citations

Abstract

This letter describes an investigation of the 2.613 micron fluorescence of trivalent uranium in CaF2 (CaF2:U3+) and the operation of a continuous solid-state maser using this transition.

DOI: 10.1103/physrevlett.8.269

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Physical Review Letters

Excitation, Relaxation, and Continuous Maser Action in the 2.613-Micron Transition of Ca F2 : U3+

Gary D. Boyd, R. J. Collins, Sergio P. S. Porto, Avigail Yariv, W. A. Hargreaves

Published Apr 1, 1962• 80 citations

Publisher

Abstract

This letter describes an investigation of the 2.613 micron fluorescence of trivalent uranium in CaF2 (CaF2:U3+) and the operation of a continuous solid-state maser using this transition.

DOI: 10.1103/physrevlett.8.269

Related papers

Spectroscopy and Optical Maser Action in Sr F2 : Sm2+

P. P. Sorokin, M. J. Stevenson, J. R. Lankard +1 more

A crystal of Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ was operated as a pulsed optical maser at temperatures close to 4.2\ifmmode^\circ\else\textdegree\fi{}K. The 6969 \AA{} output corresponds to the wavelength of an exceedingly sharp line ($\ensuremath{\Delta}\ensuremath{\nu}<0.6$ ${\mathrm{cm}}^{\ensuremath{-}1}$) in which almost all of the low-temperature fluorescence is concentrated. In contrast to what prevails in Ca ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{+2}$ masers, the output is characterized by strong relaxation oscillations. This may be explained by the large difference in the fluorescent lifetimes in the two systems. While in Ca ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ the value of $\ensuremath{\tau}$ is approximately 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ sec, in Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ it has a value of 15 msec. The reason for the large difference in $\ensuremath{\tau}$ values, in turn, depends upon the relative proximity of the long-wavelength edge of the red band to the position of the metastable $^{5}D_{0}$ level from which fluorescence occurs. Absorption measurements taken at helium temperatures on Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ show that the lowest vibrational level of the lowest lying $4f\ensuremath{-}5d$ band lies \ensuremath{\sim}600 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the position of the $^{5}D_{0}$ level while in Ca ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ there is near coincidence of the corresponding levels and consequently strong configurational mixing. Crystals of Sr ${\mathrm{Cl}}_{2}$ : ${\mathrm{Sm}}^{2+}$ were also studied in this regard and display an expected close similarity in spectral characteristics to Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ . The vibrational structure on the $4f\ensuremath{-}5d$ bands is much more pronounced, however, than in Ca ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ and Sr ${\mathrm{F}}_{2}$ : ${\mathrm{Sm}}^{2+}$ , indicating weaker coupling to the lattice in the excited $5d$ state. A tentative interpretation for the splitting of the red band seen in the absorption spectra of ${\mathrm{Sm}}^{2+}$ ions is given.A crystal of Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ was operated as a pulsed optical maser at temperatures close to 4.2\ifmmode^\circ\else\textdegree\fi{}K. The 6969 \AA{} output corresponds to the wavelength of an exceedingly sharp line ($\ensuremath{\Delta}\ensuremath{\nu}<0.6$ ${\mathrm{cm}}^{\ensuremath{-}1}$) in which almost all of the low-temperature fluorescence is concentrated. In contrast to what prevails in Ca${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{+2}$ masers, the output is characterized by strong relaxation oscillations. This may be explained by the large difference in the fluorescent lifetimes in the two systems. While in Ca${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ the value of $\ensuremath{\tau}$ is approximately 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ sec, in Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ it has a value of 15 msec. The reason for the large difference in $\ensuremath{\tau}$ values, in turn, depends upon the relative proximity of the long-wavelength edge of the red band to the position of the metastable $^{5}D_{0}$ level from which fluorescence occurs. Absorption measurements taken at helium temperatures on Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ show that the lowest vibrational level of the lowest lying $4f\ensuremath{-}5d$ band lies \ensuremath{\sim}600 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the position of the $^{5}D_{0}$ level while in Ca${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ there is near coincidence of the corresponding levels and consequently strong configurational mixing. Crystals of Sr${\mathrm{Cl}}_{2}$: ${\mathrm{Sm}}^{2+}$ were also studied in this regard and display an expected close similarity in spectral characteristics to Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$. The vibrational structure on the $4f\ensuremath{-}5d$ bands is much more pronounced, however, than in Ca${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$ and Sr${\mathrm{F}}_{2}$: ${\mathrm{Sm}}^{2+}$, indicating weaker coupling to the lattice in the excited $5d$ state. A tentative interpretation for the splitting of the red band seen in the absorption spectra of ${\mathrm{Sm}}^{2+}$ ions is given.

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Reinhard Furrer, Florian Seiff, J. Pelzl

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Investigations on the excited states of Eu2+ in CaF2-and SrF2-crystals by two-photon absorption spectroscopy

U Fritzler

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A crystal of Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

was operated as a pulsed optical maser at temperatures close to 4.2\ifmmode^\circ\else\textdegree\fi{}K. The 6969 \AA{} output corresponds to the wavelength of an exceedingly sharp line ($\ensuremath{\Delta}\ensuremath{\nu}<0.6$ ${\mathrm{cm}}^{\ensuremath{-}1}$) in which almost all of the low-temperature fluorescence is concentrated. In contrast to what prevails in Ca

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{+2}

masers, the output is characterized by strong relaxation oscillations. This may be explained by the large difference in the fluorescent lifetimes in the two systems. While in Ca

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

the value of $\ensuremath{\tau}$ is approximately 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ sec, in Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

it has a value of 15 msec. The reason for the large difference in $\ensuremath{\tau}$ values, in turn, depends upon the relative proximity of the long-wavelength edge of the red band to the position of the metastable

^{5}D_{0}

level from which fluorescence occurs. Absorption measurements taken at helium temperatures on Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

show that the lowest vibrational level of the lowest lying $4f\ensuremath{-}5d$ band lies \ensuremath{\sim}600 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the position of the

^{5}D_{0}

level while in Ca

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

there is near coincidence of the corresponding levels and consequently strong configurational mixing. Crystals of Sr

{\mathrm{Cl}}_{2}

{\mathrm{Sm}}^{2+}

were also studied in this regard and display an expected close similarity in spectral characteristics to Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

. The vibrational structure on the $4f\ensuremath{-}5d$ bands is much more pronounced, however, than in Ca

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

and Sr

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{2+}

, indicating weaker coupling to the lattice in the excited

5d

state. A tentative interpretation for the splitting of the red band seen in the absorption spectra of

{\mathrm{Sm}}^{2+}

ions is given.

Measurements are reported of absorption, emission, and activation spectra in Ca

{\mathrm{F}}_{2}

{\mathrm{Sm}}^{++}

, and also of fluorescence lifetime. A revised level scheme is proposed. Observations of optical maser effects were made at liquid hydrogen and liquid helium temperatures over a wide range of pumping intensities. For illumination in the 6400-A band, the threshold intensity of illumination was about 20 w ${\mathrm{cm}}^{\ensuremath{-}2}$. Observations are reported of the dependence of the intensity of the maser beam on the pumping intensity. Photographic observations, made both with or without a Fabry-Perot etalon, show that on one particular sample five distinct frequencies were present in the maser signal, and that the number of modes excited was of the order of 1000.