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Applied Optics

Dy^2+:CaF_2 saturable-absorber Q switch for the ruby laser

Yen‐Kuang Kuo, Wei Chen, Robert D. Stultz, Milton Birnbaum

Published Sep 20, 1994• 13 citations
Publisher

Abstract

Passive Q switching of a flash-lamp-pumped ruby laser has been demonstrated with a Dy(2+):CaF(2) saturable absorber at room temperature. Typically a single Q-switched pulse of 4.5 mJ and 94 ns was observed. At 694 nm, the ground-state absorption cross section and the excited-state absorption cross section of the Dy(2+):CaF(2) absorber were found to be 1.2 × 10(-18) cm(2) and 0.9 × 10(-18) cm(2) respectively, with a four-level slow-relaxing saturable-absorber model.

DOI
10.1364/ao.33.006348

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7B4 - Absorption and emission properties of optically pumped ruby

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Several experiments on optically excited ruby are described. First, absorption transitions initiated from the metastable states,t\min{2}\max{3}2Eandt\min{2}\max{3}2T1, are investigated in the photon energy range from 5500 to 45 000 cm-1. The absorption spectrum of these excited states is determined in both\pi-and σ-polarizations and assignments for the observed absorption bands are achieved. Obtained results are compared with other experiments reported in the literature. Next, emission properties of pink ruby are studied in the region near theRlines. The emission spectrum is determined point by point by means of intense flash excitation. The observed weak bands are ascribed to theR'and phonon assistedRtransitions. Laser actions in these bands are discussed and experimental results on phonon terminated laser amplification are presented. An experiment using a giant pulse as an excitation source reveals that the transition time fromt\min{2}\max{3}2Etot\min{2}\max{3}2T1is shorter than a fraction of 1μs at room temperature.

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Laser with a saturable absorber

Thomas Erneux, P. Glorieux

In a laser with a saturable absorber (LSA), two spatially separated cells are placed in the laser cavity as shown in Figure 8.1. The roles of the two cells are quite different: one of them is pumped so that the atoms have a positive population inversion (active or amplifying medium); the other one is left with a negative population inversion (passive or absorbing medium). As these two media are in general different, they saturate at different power levels. The most interesting case corresponds to the situation where the absorber saturates more easily than the active medium, introducing nonlinear losses inside the cavity. This new nonlinearity is responsible for two phenomena. An LSA may exhibit optical bistability, i.e. two distinct stable steady states may coexist for a range of values of a parameter. It may also produce pulsating intensity oscillations which have been called “passive Q-switching” (PQS) in contrast to “active Q-switching” experiments such as the “gain switching” experiments discussed in Section 1.3.2. The interest in LSAs varied very much over time, with peaks in the late 1960s for their large intensity pulses, in the mid 1980s for their chaotic outputs, and in the late 1990s for the design of compact microlasers. Historically, physicists trying to explain the irregular intensity pulses delivered by the ruby laser suspected the possible destabilizing role of a saturable absorber. Shimoda proposed that the nonlinear losses generated by a saturable absorber could explain this phenomenon.

Cambridge University Press eBooks•Apr 29, 2010•0 citations
Passive Q switching of a flash-lamp-pumped ruby laser has been demonstrated with a Dy(2+):CaF(2) saturable absorber at room temperature. Typically a single Q-switched pulse of 4.5 mJ and 94 ns was observed. At 694 nm, the ground-state absorption cross section and the excited-state absorption cross section of the Dy(2+):CaF(2) absorber were found to be 1.2 × 10(-18) cm(2) and 0.9 × 10(-18) cm(2) respectively, with a four-level slow-relaxing saturable-absorber model.
The degree of the decrease in the population of ground-state Cr ions in ruby brought about by optical pumping with Xe flash light has been measured as a function of time under Q-switching operation. The measurement has been made by observing the decrease in absorbing power of the ruby crystal for a probe light (Hg 5461Å), (γ), while Q-switching with a rotating prism or saturable absorber (Cryptocyanine). Observations of rapid change of (γ) due to the emission of giant pulse laser light have been carried out, with the very satisfactory results. At the occurrence of a giant pulse, the higher the initial value of (γ) is, the lower becomes the final value of (γ).
A time varying macroscopic magnetization of ruby is observed at room temperature by selectively exciting the Cr 3+ ions with a right- and a left circularly polarized light of a Q -switched ruby laser from one of the ground 4 A 2 multiplets to a proper component of the upper \bar E ( 2 E ) multiplets. Dependence of such a magnetization in the Z -direction on the irradiation power, the ellipticity and the magnetic field was measured with a pick-up coil. The signal had a value of 1.7×10 -4 emu/g at the irradiation of 67 mJ. The relaxation time of the ground state was estimated from the decay to be about 180 ns in zero magnetic field. The signal changed with the ellipticity of the exciting light, and the amplitude of the signal was always proportional to the intensity of the excitation. These experimental results were quantitatively explained by a theoretical analysis for the time varying optically induced magnetization.
Several experiments on optically excited ruby are described. First, absorption transitions initiated from the metastable states,t\min{2}\max{3}2Eandt\min{2}\max{3}2T1, are investigated in the photon energy range from 5500 to 45 000 cm-1. The absorption spectrum of these excited states is determined in both\pi-and σ-polarizations and assignments for the observed absorption bands are achieved. Obtained results are compared with other experiments reported in the literature. Next, emission properties of pink ruby are studied in the region near theRlines. The emission spectrum is determined point by point by means of intense flash excitation. The observed weak bands are ascribed to theR'and phonon assistedRtransitions. Laser actions in these bands are discussed and experimental results on phonon terminated laser amplification are presented. An experiment using a giant pulse as an excitation source reveals that the transition time fromt\min{2}\max{3}2Etot\min{2}\max{3}2T1is shorter than a fraction of 1μs at room temperature.
In a laser with a saturable absorber (LSA), two spatially separated cells are placed in the laser cavity as shown in Figure 8.1. The roles of the two cells are quite different: one of them is pumped so that the atoms have a positive population inversion (active or amplifying medium); the other one is left with a negative population inversion (passive or absorbing medium). As these two media are in general different, they saturate at different power levels. The most interesting case corresponds to the situation where the absorber saturates more easily than the active medium, introducing nonlinear losses inside the cavity. This new nonlinearity is responsible for two phenomena. An LSA may exhibit optical bistability, i.e. two distinct stable steady states may coexist for a range of values of a parameter. It may also produce pulsating intensity oscillations which have been called “passive Q-switching” (PQS) in contrast to “active Q-switching” experiments such as the “gain switching” experiments discussed in Section 1.3.2. The interest in LSAs varied very much over time, with peaks in the late 1960s for their large intensity pulses, in the mid 1980s for their chaotic outputs, and in the late 1990s for the design of compact microlasers. Historically, physicists trying to explain the irregular intensity pulses delivered by the ruby laser suspected the possible destabilizing role of a saturable absorber. Shimoda proposed that the nonlinear losses generated by a saturable absorber could explain this phenomenon.