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Journal of Applied Physics

Optical Maser Emission from Trivalent Praseodymium in Calcium Tungstate

Avigail Yariv, Sergio P. S. Porto, KURT NASSAU

Published Aug 1, 1962• 52 citations
Publisher

Abstract

Coherent emission at 1.047 μ from trivalent praseodymium in calcium tungstate was observed. This emission coincides with strong infrared fluorescence at the same wavelength and was found to be stimulated mostly by absorption of blue light by the 3P0, 3P1, and 3P2 bands. The emission corresponds to a 1G4→3H4 transition with the terminal level 377 cm−1 from the ground state. The oscillation threshold was the same at 4.2°, 20°, and 78°K. No stimulated emission was observed at room temperature. The lifetime of the metastable state 1G4 is 50×10−3 sec. A new technique used to measure the lifetime is described.

DOI
10.1063/1.1729008

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Physical Review•Aug 1, 1961•162 citations
Coherent emission at 1.047 μ from trivalent praseodymium in calcium tungstate was observed. This emission coincides with strong infrared fluorescence at the same wavelength and was found to be stimulated mostly by absorption of blue light by the 3P0, 3P1, and 3P2 bands. The emission corresponds to a 1G4→3H4 transition with the terminal level 377 cm−1 from the ground state. The oscillation threshold was the same at 4.2°, 20°, and 78°K. No stimulated emission was observed at room temperature. The lifetime of the metastable state 1G4 is 50×10−3 sec. A new technique used to measure the lifetime is described.
Infrared fluorescence and phonon-terminated stimulated emission from V2+ ions in MgF2 is reported. Fluorescence is produced in transitions from the first excited state 4T2(4F) to the ground state 4A2(4F). Stimulated emission occurs in the vibronic sideband at 1.1217 μ (8915 cm−1) and lies 1166 cm−1 from the no-phonon line. A gain curve calculated from the optical spectra predicts an oscillation frequency in reasonable agreement with the observed frequency, with a cross section for stimulated emission of 8×10−21 cm2. From the effect of excited state absorption on the gain profile it is concluded that the excited state absorption cross section at the maser frequency is <3×10−21 cm2.
A crystal of SrF2{\mathrm{F}}_{2}F2​: Sm2+{\mathrm{Sm}}^{2+}Sm2+ 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 CaF2{\mathrm{F}}_{2}F2​: Sm+2{\mathrm{Sm}}^{+2}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 CaF2{\mathrm{F}}_{2}F2​: Sm2+{\mathrm{Sm}}^{2+}Sm2+ the value of $\ensuremath{\tau}$ is approximately 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ sec, in SrF2{\mathrm{F}}_{2}F2​: Sm2+{\mathrm{Sm}}^{2+}Sm2+ 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 5D0^{5}D_{0}5D0​ level from which fluorescence occurs. Absorption measurements taken at helium temperatures on SrF2{\mathrm{F}}_{2}F2​: Sm2+{\mathrm{Sm}}^{2+}Sm2+ 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 5D0^{5}D_{0}5D0​ level while in CaF2{\mathrm{F}}_{2}F2​: Sm2+{\mathrm{Sm}}^{2+}Sm2+ there is near coincidence of the corresponding levels and consequently strong configurational mixing. Crystals of SrCl2{\mathrm{Cl}}_{2}Cl2​: Sm2+{\mathrm{Sm}}^{2+}Sm2+ were also studied in this regard and display an expected close similarity in spectral characteristics to SrF2{\mathrm{F}}_{2}F2​: Sm2+{\mathrm{Sm}}^{2+}Sm2+. The vibrational structure on the $4f\ensuremath{-}5d$ bands is much more pronounced, however, than in CaF2{\mathrm{F}}_{2}F2​: Sm2+{\mathrm{Sm}}^{2+}Sm2+ and SrF2{\mathrm{F}}_{2}F2​: Sm2+{\mathrm{Sm}}^{2+}Sm2+, indicating weaker coupling to the lattice in the excited 5d5d5d state. A tentative interpretation for the splitting of the red band seen in the absorption spectra of Sm2+{\mathrm{Sm}}^{2+}Sm2+ ions is given.
High resolution, absolute excited-state absorption (ESA) spectra, at room temperature, from the long-lived 3F4 energy level of several crystals doped with trivalent thulium (Tm3+) ions have been measured employing high-brightness narrowband (FWHM <30 nm) light emitting diodes (LEDs) as a probe wavelength. The aim of this investigation was to determine the strength of ESA channels at wavelengths addressable by commercially available semiconductor laser diodes operating around 630-680 nm. The favourable lifetime of the 3F4 manifold and negligible ground-state absorption (GSA) for the red-wavelength second-step excitation, ensures a direct and efficient route for a dual-wavelength pumping scheme of the thulium ion, which will enable blue-green laser emission from its 1G4 upper-laser level.
We report on the first observation of low temperature pulsed blue and orange laser emissions in Pr3+:YAG. Furthermore, we compare these results with similar observations in YLiF4 and YAlO3 doped crystals. Pulsed laser oscillations were obtained in crystals with uncoated surfaces by direct excitation of one of the relevant Stark components of the 3P0, 3P1 or 3P2 states. A carefull spectroscopic analysis of all these systems allows to clearly identify the laser transitions as arising from the 3P0 metastable state, the lifetime of which has been measured using a nanosecond pumped dye laser.
Short pulse laser-induced fluorescence experiments on the lowest-energy electronic states (υ<10−4 cm−1) of trivalent praseodymium ions are reported. Crystals of lanthanum trichloride with a range of Pr3+ concentrations were examined. We compute cross relaxation and upconversion coefficients for the metastable energy levels using a standard rate equation analysis. The limitations of the rate equation approach are examined with a focus on the underlying dynamics of this rare-earth system. The implications of these results for laser emission in the 1.3–7.2 μm spectral range are discussed.
Measurements are reported of absorption, emission, and activation spectra in CaF2{\mathrm{F}}_{2}F2​: Sm++{\mathrm{Sm}}^{++}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.