We report the results of time–resolved optical holeburning of Er3+ ions in YLiF4 (0.02%). In earlier work for H//c we described the time evolution of holes burned at 33kG using laser scanning over a frequency of 40MHz1 and we reported, using larger scans, the occurence of optical side holes. We now describe results for H⊥c with scans > 400 MHz using a new Zeeman technique for frequency scanning the optical transition frequencies which allow one to study the time evolution of the holes and their associated sideholes. The hole lineshapes evolve with time reaching a linewidth of ≃ 10 MHz after 600 μs. We identify the source of the time evolution of the hole shape as spectral diffusion resulting from mutual spin flips of the surrounding fluorine nuclei whose flip rates are strongly modified from the bulk rates by the presence of the large magnetic moment of the Er3+ ion which produces a "frozen core". A computer simulation which takes into account the details of the dynamics of the frozen core successfully describes the time evolution of the holes, confirming the dominant role of F nuclear spin flips.
We use spectral hole burning to investigate spin dynamics within the electronic Zeeman sublevels of the ground state of the erbium ions in erbium-doped fibers (EDF). Conducted at ultra-low temperatures and under varying magnetic fields, our study reveals distinct changes in spin relaxation dynamics across different conditions. We identified three decay components at approximately 7 mK, with one achieving spin lifetimes of over 9 hours under optimal conditions, while two components were observed at higher temperatures. The fairly stable relative weights of the decay components across conditions suggest distinct ion populations contributing to the observed relaxation dynamics. While earlier studies struggled to account for all decay components at higher temperatures, our approach successfully models spin dynamics across all observed decay components, using a consistent set of underlying mechanisms, including spin flip-flop interactions, direct coupling to two-level systems, and Raman-type processes, and distinguishes the decay components by the strengths with which these mechanisms contribute. These results suggest EDFs' potential as a promising candidate for quantum memory applications, with further room for optimization.
We present measurements of Zeeman-level population lifetimes in
Er3+:Y2SiO5 at low magnetic fields and low temperatures. Using spectral hole burning spectroscopy, we investigate the dynamics and temperature dependence of the hole structure due to the Zeeman interaction. Evidence for population storage in Zeeman levels with lifetimes of up to 130 ms is found in the form of long-lived spectral holes and antiholes. We also observe that a subset of the erbium ions exhibit very long-lived holes with lifetimes as long as 60 s at 2.8 K.
The mechanisms and effects of spectral diffusion for optical transitions of paramagnetic ions have been explored using the inhomogeneously broadened 1536 nm $^{4}\mathrm{I}_{15∕2}\ensuremath{\rightarrow}^{4}\mathrm{I}_{13∕2}$ transition in
Er3+:Y2SiO5. Using photon echo spectroscopy, spectral diffusion was measured by observing the evolution of the effective coherence lifetimes over time scales from $1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$ to 20 ms for magnetic-field strengths from 0.3 to 6.0 T, temperatures from 1.6 to 6.5 K, and nominal
Er3+ concentrations of 0.0015%, 0.005%, and 0.02%. To understand the effect of spectral diffusion on material decoherence for different environmental conditions and material compositions, data and models were compared to identify spectral diffusion mechanisms and microscopic spin dynamics. Observations were successfully modeled by ${\mathrm{Er}}^{3+}\ensuremath{-}{\mathrm{Er}}^{3+}$ magnetic dipole interactions and
Er3+ electron spin flips driven by the one-phonon direct process. At temperatures of 4.2 K and higher, spectral diffusion due to
89Y nuclear spin flips was also observed. The success in describing our extensive experimental results using simple models provides an important capability for exploring larger parameter spaces, accelerating the design and optimization of materials for spatial-spectral holography, and spectral hole-burning devices. The broad insight into spectral diffusion mechanisms and dynamics is applicable to other paramagnetic materials, such as those containing
Yb3+ or
Nd3+.
We demonstrate a new mechanism for optical spectral hole burning in which population is stored in electronic Zeeman sublevels. This is shown by optical pumping the ground-state Kramers doublet of the
4I9/2${\mathrm{\ensuremath{\leftrightarrows}}}^{2}$
H11/2 (6248.9 A\r{}) and
4I9/2${\mathrm{\ensuremath{\leftrightarrows}}}^{4}$
G5/2 (5777.1 A\r{}) transitions of
LaF3:
Nd3+ with a narrow-band cw dye laser. Experiments were carried out at 1.6 K in external fields of \ensuremath{\sim}100 G. The Zeeman shift of the resulting antiholes and holes makes an assignment of these structures possible. Hole recovery times of hundreds of milliseconds are shorter than expected at these low temperatures and fields and provide evidence for optical spectral diffusion caused by mutual spin flips in the ground state.
Narrow spectral holes in the absorption lines of Er doped crystals have been explored as references for frequency stabilizing external cavity diode lasers at the important 1.5 μm optical communication wavelength. Allan deviations of the beat signal between two independent stabilized lasers as low as 200 Hz over 10 ms integration time have been achieved using regenerative spectral holes in Er:Y2SiO5 and Er:KTP, while drift was reduced to ~ 7 kHz/min by incorporating the inhomogeneous absorption line as a fixed reference. During active stabilization, the transient spectral hole was continuously regenerated as hole burning balanced relaxation. In contrast, persistent spectral holes in Er:D:CaF2, with lifetimes of several weeks, provided programmable and transportable secondary frequency references that maintained sub-kilohertz stability over several seconds and enabled 6 kHz stability over 3 1.6 10 s × . The error signal was derived from the spectral hole transmission using frequency modulation spectroscopy. A servo amplifier applied fast frequency corrections to the injection current of the laser diode and slower adjustments to the piezo-driven feedback prism plate. These stabilized lasers provide ideal sources for spectral hole burning applications based on optical coherent transients, where laser stability is required over the storage time of the material. Since the lifetime of the frequency reference is exactly the material storage time, this requirement is automatically met by using our technique. This was demonstrated in Er:Y2SiO5 and successfully transferred to high-bandwidth signal processing applications. The material Er:Y2SiO5 was optimized for these applications. The I15/2 and I13/2 crystal field levels were site-selectively determined by absorption and fluorescence spectroscopy. The excited state lifetime was measured to be 11.4 ms for site 1 and 9.2 ms for site 2. Zeeman experiments and two-pulse photon echo spectroscopy as a function of magnetic field orientation were used to determine the anisotropic electronic g-values for both Er sites and established a preferred magnetic field orientation for minimizing homogeneous line broadening by spectral diffusion. The spectral diffusion was characterized by stimulated photon echo spectroscopy and successfully described with established theories. In a 0.02 atomic percent Er:Y2SiO5 crystal at B = 0.8 T and T = 1.6 K, line broadening became significant after 10 μs, increasing the homogeneous linewidth from 7.5 kHz to 75 kHz after 120 μs. Spectral diffusion, primarily caused by direct phonon driven Er spin-flips in the ground state, can be controlled to negligible levels with proper magnetic field strength and orientation, temperature, and erbium concentration. In optimizing Er:Y2SiO5, the narrowest optical resonance in any solid-state material of 73 Hz was measured.