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Single crystal fibers combine the great specific surface area of fibers and the single crystal property of the bulk crystal which shows great potential for a high-power laser. For an Er-doped crystal, due to the fluorescence quenching at the 3 μm wavelength, high Er doping is necessary to increase the fluorescent up-conversion for the breaking limitation. However, a high Er doping concentration must lead to high heat accumulation, resulting in poor laser performance. Compared with an Er-doped bulk crystal, Er-doped SCF has the great potential to remove the heat in the crystal, and it is easy to obtain a high power. In this paper, Er: Y3Sc2Ga3O12 (Er: YSGG) single crystals were successfully grown using the micro-pulling-down method (μ-PD). Owing to the stably grown interface, the diameter of the crystal is 2 mm with a length up to 80 mm. Then, the measurements of Laue spots and Er3+ distribution indicated that our crystals have a high quality. Based on the as-prepared Er: YSGG SCF, the continuous-wave (CW) laser operations at 2794 nm were realized. The maximum output was 166 mW with a slope efficiency of up to 10.99%. These results show that Er: YSGG SCF is a suitable material for future high-power 3 μm laser operation.

This paper proposes a Faraday anomalous dispersion optical filter that uses rare earth-doped crystals to overcome the limitations of current atomic filtering technology, which include limited working wavelength and Doppler broadening. The paper analyses Er 3+ : LiYF 4 1530 nm as an example filter. The results show that the proposed filter achieves high transmission while maintaining an ultra-narrow bandwidth transmission spectrum. The maximum transmission efficiency reaches 94.8% with a transmission bandwidth of hundred trillions HZ. The position of the transmission peak can be tuned by adjusting the size of the magnetic field, enabling the conversion of the transmission spectrum between the line center and the line wing.

A long-lived and multimode quantum memory is a key component needed for the development of quantum communication. Here we present temporally multiplexed storage of five photonic polarization qubits encoded onto weak coherent states in a rare-earth-ion doped crystal. Using spin refocusing techniques we can preserve the qubits for more than half a millisecond. The temporal multiplexing allows us to increase the effective rate of the experiment by a factor of five, which emphasizes the importance of multimode storage for quantum communication. The fidelity upon retrieval is higher than the maximum classical fidelity achievable with qubits encoded onto single photons and we show that the memory fidelity is mainly limited by the memory signal-to-noise ratio. These results show the viability and versatility of long-lived, multimode quantum memories based on rare-earth-ion doped crystals.

The current article is the first to study the influence of an anionic dye on the properties of a single sulphamic acid crystal (SA). By using a slow evaporation method, single crystals of pure and methyl orange (MO)-doped sulphamic acid (MOSA) were synthesized. Powder X-ray diffraction (XRD) was used to investigate the crystalline nature of the grown crystals. The Scherrer method was employed to calculate the crystallite size of both formed crystals and was compared to the W–H method. The presence of several functional groups was confirmed by FTIR spectroscopy. At the site where MO dye was incorporated into the SA lattice, UV–Vis–NIR absorption spectra revealed three different absorption bands. Based on transmittance measurements, different optical constants such as optical band gap (Eg), extinction coefficient (k), refractive index (n) and optical conductivity (σ) were determined for both the samples. The thermal stability and decomposition temperature of doped crystals were found to be substantially enhanced. The doped crystal's increased optical characteristics and thermal stability prove that they are viable for optoelectronic applications.

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 3 + :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 3 + :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.

Single crystals of pure potassium dihydrogen phosphate (KDP) and Reactive Orange 16 or Remazol Brilliant Orange dye-doped (0.1, 0.2 and 0.3 mol%) KDP single crystals were grown by slow evaporation method with the vision to improve the properties of pure KDP crystal. Enhanced dielectric, optical, thermal and NLO properties have been achieved by dye doping. The crystallinity and phase purity of the grown crystals were analysed by PXRD. The identification of various functional groups and dye incorporation in the grown crystals was confirmed qualitatively by FTIR analysis. The linear optical study on pure and dye-doped crystals was carried out using UV–Vis–NIR spectroscopy. The optical band gap, extinction coefficient, refractive index and optical conductivity were calculated using the transmittance spectra for all the samples. The thermal stability and the decomposition temperature were found to increase with the concentration of the dopant. This indicates the high quality of the crystal as well as its perfection. The SHG efficiency measurements were taken for the grown crystals and found that the SHG efficiency increases with doping concentration. The enhanced optical constants, thermal stability and second harmonic generation ability confirm the suitability of the grown crystals for solid-state laser materials.

Herein, we delineate the enhancement of the dielectric properties of an anionic dye doped triglycine acetate crystal for the first time. Single crystals of pure triglycine acetate (TGAc) and reactive orange 16 (RO16) dye-doped (0.01, 0.03 mol%) triglycine acetate were synthesized with an intention to enhance the strengths of pure TGAc crystal using slow evaporation process. The crystalline structure and phase purity of the grown crystals were analyzed using Powder XRD studies. The frequency dependence of real and imaginary part of dielectric constant, loss tangent, real and imaginary part of impedance, electrical modulus and ac electrical conductivity have been investigated. The dielectric constant and dielectric loss for the grown crystals, have been found to decrease with increasing frequency. The decrease in permittivity and dielectric loss with an increase in applied field frequency is as per Maxwell–Wagner theory. The Cole–Cole plot implies that the mechanism of conduction is mainly due to bulk resistance. The enhanced dielectric constant of the doped crystals confirms the appropriateness of the developed crystals for energy storage capacitor applications.

This present work aims to investigate the influence of organic dyes (methyl orange (MO), hexamethyl pararosaniline chloride (HPC)) doped with potassium hydrogen phthalate ammonium sulfate (KHPA) crystals. The solution-grown dye doped KHPA were examined using powder-XRD, FT-IR, UV–visible spectroscopy, dielectric, microhardness, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and antibacterial activity studies. PXRD spectrum revealed that the solution-grown crystal belongs to orthorhombic system with excellent cell parameters. The grain size of the dye doped KHPA crystal was found to be D  = 26.609 nm. The FTIR spectral analysis was identified the presence of various functional groups and the UV spectrum showed absorbance around 280 nm for the solution-grown dye doped crystals of KHPA. The Tauc’s plots of pure KHPA exhibited band gap energy of 4.5 eV, whereas the band gap energies of MO and PHC doped KHPA crystals showed 4.25 eV and 4.13 eV, respectively. Thermal stability of the as-grown dye doped KHPA crystals was analyzed by TGA and DTA techniques. The dielectric study revealed that the dielectric constant and dielectric loss decreased while increasing the frequency, whereas the microhardness study showed that the dye-doped crystals belong to the soft material category. CV of dye-doped crystals exhibited a strong reduction potential wave at − 0.75 V for HPC doped KHPA and − 0.6 V for MO doped KHPA. EIS study exhibited the decrease in impedance with change in frequency indicating a negative temperature coefficient of resistance and low ion mobility of the dye doped KHPA crystals. The antibacterial study revealed that the Gram-negative bacteria have more resistivity than Gram-positive bacteria.

Photon loss in optical fibers prevents long-distance distribution of quantum information on the ground. Quantum repeater is proposed to overcome this problem, but the communication distance is still limited so far because of the system complexity of the quantum repeater scheme. Alternative solutions include transportable quantum memory and quantum-memory-equipped satellites, where long-lived optical quantum memories are the key components to realize global quantum communication. However, the longest storage time of the optical memories demonstrated so far is approximately 1 minute. Here, by employing a zero-first-order-Zeeman magnetic field and dynamical decoupling to protect the spin coherence in a solid, we demonstrate coherent storage of light in an atomic frequency comb memory over 1 hour, leading to a promising future for large-scale quantum communication based on long-lived solid-state quantum memories. Quantum memories are key components for quantum communication, but current storage times are still too short. Here, the authors use the atomic frequency comb protocol in a zero-first-order-Zeeman field to coherently store an optical pulse for an hour in a cryogenically cooled rare-earth doped crystal.

After nearly 50 years of searching, the vacuum ultraviolet 229 Th nuclear isomeric transition has recently been directly laser excited 1 , 2 and measured with high spectroscopic precision 3 . Nuclear clocks based on this transition are expected to be more robust 4 , 5 than and may outperform 6 , 7 current optical atomic clocks. These clocks also promise sensitive tests for new physics beyond the standard model 5 , 8 , 9 , 10 , 11 – 12 . In light of these important advances and applications, a substantial increase in the need for 229 Th spectroscopy targets in several platforms is anticipated. However, the growth and handling of high-concentration 229 Th-doped crystals 5 used in previous measurements 1 , 2 – 3 , 13 , 14 are challenging because of the scarcity and radioactivity of the 229 Th material. Here we demonstrate a potentially scalable solution to these problems by performing laser excitation of the nuclear transition in 229 ThF 4 thin films grown using a physical vapour deposition process, consuming only micrograms of 229 Th material. The 229 ThF 4 thin films are intrinsically compatible with photonics platforms and nanofabrication tools for integration with laser sources and detectors, paving the way for an integrated and field-deployable solid-state nuclear clock with radioactivity up to three orders of magnitude smaller than typical 229 Th-doped crystals 1 , 2 – 3 , 13 . The high nuclear emitter density in 229 ThF 4 also potentially enables quantum optics studies in a new regime. Finally, we present the estimation of the performance of a nuclear clock based on a defect-free ThF 4 crystal. Laser excitation of the  229 Th isomer, potentially relevant for nuclear clocks, is reported in thorium fluoride thin films, which are less radioactive and amenable to integration compared with existing thorium-doped crystals.