Neodymium-doped Crystals Research Articles

Efficient optical pumping using hyperfine levels in 145Nd3+:Y2SiO5 and its application to optical storage

Efficient optical pumping is an important tool for state initialization in quantum technologies, such as optical quantum memories. In crystals doped with Kramers rare-earth ions, such as erbium and neodymium, efficient optical pumping is challenging due to the relatively short population lifetimes of the electronic Zeeman levels, of the order of 100 ms at around 4 K. In this article we show that optical pumping of the hyperfine levels in isotopically enriched 145Nd :Y2SiO5 crystals is more efficient, owing to the longer population relaxation times of hyperfine levels. By optically cycling the population many times through the excited state a nuclear spin flip can be forced in the ground state hyperfine manifold, in which case the population is trapped for several seconds before relaxing back to the pumped hyperfine level. To demonstrate the effectiveness of this approach in applications we perform an atomic frequency comb memory experiment with 33% storage efficiency in 145Nd :Y2SiO5, which is on a par with results obtained in non-Kramers ions, e.g. europium and praseodymium, where optical pumping is generally efficient due to the quenched electronic spin. Efficient optical pumping in neodymium-doped crystals is also of interest for spectral filtering in biomedical imaging, as neodymium has an absorption wavelength compatible with tissue imaging. In addition to these applications, our study is of interest for understanding spin dynamics in Kramers ions with nuclear spin.

Comparative analysis of the use of various solid-state laser media for the self-starting of four-wave PCW generation in a loop laser resonator

A generalised theory has been used to carry out a comparative analysis of the use of various four-level and quasi-threelevel media for the self-starting of degenerate four-wave mixing PCW generation directly in a laser medium placed in a loop resonator. It has been shown that quasi-three-level media can compete with four-level media at long upper laser level lifetimes and increased pump intensities. The most attractive solid-state laser media for four-wave PCW generation have been identified thathave the highest deposited energy at a given pump intensity. In addition to neodymium-doped crystals, which are already widely used for four-wave PCW generation, promising materials are fourlevel chromium-doped media, e.g. alexandrite and Cr : LiCAF, and quasi-three-level media with the longest upper laser level lifetime, such as Yb : YAG and Tm, Ho : YAG, at high pump intensities.

Low‐wavelength emission of Nd‐doped lasers

AbstractThis paper gives an overview of the results obtained with diode‐pumped Neodymium‐doped crystals operating below 900 nm. Operation at such low wavelengths requires considering the strong thermal population of the lower level of the laser transition. Based on a theoretical study and simulations, the paper presents the challenges related to the design of these three‐level lasers. Experimental results are given with Nd:YAG and Nd:vanadate crystals. It is explained how to deal with the line competition with emission at 946 nm or 912 nm. Finally, intracavity second‐harmonic generation is presented. The output powers reach a few hundred mW at wavelengths below 450 nm. Hence, the paper demonstrates the potential of Nd‐doped diode‐pumped solid‐state lasers for applications in the blue range, in replacement of gas lasers such as helium‐cadmium lasers.

Circular dichroism of some Nd-doped crystals of the langasite family

The absorption and circular-dichroism spectra of neodymium-doped crystals of langasite La3Ga5SiO14 and the compounds La3Ga5.5Nb0.5O14 and Pb3Ga2Ge3.92Si0.08O14, isostructural with langasite, are investigated in the wavelength range 320–940 nm. Electronic transitions in Nd atoms, which substitute the main cation of the salts (La or Pb) in the positions with the local symmetry C2, are observed in the spectra. All transitions observed in the absorption spectrum are also active in the circular-dichroism spectrum. Detailed analysis is performed for several (well separated) bands: Dipole strengths D ok , rotation strengths R ok , and the anisotropy factors G ok are calculated. Some specific features of the spectra obtained are noted and their possible relationship with the structure of impurity centers of neodymium and effect on the intensity of the Stark components are discussed.

Properties of Nd^3+-doped and undoped tetragonal PbWO_4, NaY(WO_4)_2, CaWO_4, and undoped monoclinic ZnWO_4 and CdWO_4 as laser-active and stimulated Raman scattering-active crystals

Spectroscopic, laser, and chi((3)) nonlinear optical properties of tetragonal PbWO(4), NaY(WO(4))(2), CaWO(4), and monoclinic CdWO(4) and ZnWO(4) were investigated. Particular attention was paid to Nd(3+)-doped and undoped PbWO(4) and NaY(WO(4))(2) crystals. Their absorption and luminescence intensity characteristics, including the peak cross sections of induced transitions, were determined. Pulsed and continuous-wave lasing in the two 4F(3/2)-->4I(11/2) and 4F(3/2)-->4I(13/2) channels was excited. For these five tungstates, highly efficient (greater than 50%) multiple Stokes generation and anti-Stokes picosecond generation were achieved. All the observed scattered laser components were identified. These results were analyzed and compared with spectroscopic data from spontaneous Raman scattering. A new crystalline Raman laser based on PbWO(4) was developed for the chi((3)) conversion frequency of 1-microm pump radiation to the first Stokes emission with efficiency up to 40%. We classify all the tungstates as promising media for lasers and neodymium-doped crystals for self-stimulated Raman scattering lasers.

Picosecond nonradiative processes in neodymium-doped crystals and glasses:: Mechanism for the energy gap law

We present measurements of the 4 G 7/2 emission lifetime for 26 Nd-doped crystals and glasses, including phosphates, silicates, oxides, garnets, apatites, and fluorides. The fluorescent decays were found to range from 70 ps to 41 ns, depending on the host medium. We show that the 4 G 7/2 emission lifetime is correlated to the 4 I 11/2 relaxation time to within a factor of two, by comparing the present results with previous directly-determined 4 I 11/2 lifetimes. This 4 G 7/2 – 4 I 11/2 correlation is useful because the 4 I 11/2 state is the terminal level for the common 1.06 μm Nd-laser transition, while the 4 G 7/2 emission time can be measured in a relatively straightforward manner. A model of nonradiative decay based on dipole–dipole energy transfer is developed and found to be supported by our data. It allows independent calculation of the parameters of the energy gap law, in addition to fitting the nonradiative lifetime data.

Potential for temperature sensor applications of highly neodymium-doped crystals and fiber at up to approximately 1000 °C

This work reports on the thermographic characteristics and their potential for use, in fiber optic temperature sensors, of a range of neodymium-doped materials. Their comparative value for low-cost, simple sensors is discussed, using both crystalline materials in the bulk form and a specimen of highly doped, multimode neodymium fiber. The effects of annealing of the bulk materials are discussed in light of their suitability for such sensor applications.

Direct measurements of the terminal laser level lifetime in neodymium-doped crystals and glasses

We have measured the terminal level lifetime (τ11/2) for the 1-μm neodymium transition in several laser media, using a novel pump (2.41-μm) and probe (1.06-μm) technique. This method allows us to populate the 4I13/2 level directly and subsequently to monitor the terminal level 4I11/2 population as a function of time by observing the change in integrated fluoresence of the 0.88-μm emission for each time delay between the pump and the probe pulses. We developed a computer model to analyze the data and determined the upper and lower limits for the τ11/2 lifetime. The results for some of the materials investigated are 115–225 ps for Nd:Y3Al5O12, 250–450 ps for Nd:LG-750 (phosphate glass), 535–740 ps for Nd:LG-660 (silicate glass), 896–1900 ps for Nd:YAlO3, and 10.5–20 ns for Nd:YLiF4. In addition, we found the lifetimes to be independent of the neodymium doping concentration for the phosphate and silicate glass samples investigated.

The dielectric constants of CaWO4, Nd/CaWO4 and Gd/CaWO4

The dielectric constants and loss for pure single crystals of calcium tungstate and for neodymium- and gadolinium-doped crystals have been measured from 1 to 40 MHz. At 20‡ C the values for pure calcium tungstate areea′ = 11.3±0.4,ec′ = 9.1±0.4, at 1 MHz. These agree closely with Brower and Fang's data and increase very slightly with frequency. Doping at levels of less than 1.0 at.% produced no measurable change inea′ orec′. The dielectric loss, tanδ, which was isotropic, was about 5×10−3 for all specimens at 1 MHz; at higher frequencies, tan‡ increased and, in the neodymium-doped crystals, the high frequency loss was found to be concentration dependent.

Spectroscopic properties and laser characteristics of neodymium-doped crystals of calcium fluorophosphate

Spectroscopic properties and laser characteristics of neodymium-doped crystals of calcium fluorophosphate

An X-ray diffraction topographic study of single crystals of melt-grown yttrium aluminium garnet

Melt-grown crystals of yttrium aluminium garnet usually exhibit an optically imperfect central core region associated with the formation of facets on the solid/liquid interface during growth. The nature of the optical inhomogeneity of the core region, and the general defect structure of the crystals, was investigated by the technique of X-ray diffraction topography. The core region, which showed an elastic strain effect, contained straight growth striations reflecting the development of facets. Comparison was made between undoped and neodymium-doped crystals, and between crystals grown on and growth axes. Impurity striations were thought to be caused by temperature oscillations in the melt ahead of the growing interface. Dislocations, which were observed in the outer regions of the crystals, were sometimes nucleated at inclusions.