Optical Pumping Research Articles

Titanium:sapphire-on-insulator integrated lasers and amplifiers.

Titanium:sapphire (Ti:sapphire) lasers have been essential for advancing fundamental research and technological applications, including the development of the optical frequency comb1, two-photon microscopy2 and experimental quantum optics3,4. Ti:sapphire lasers are unmatched in bandwidth and tuning range, yet their use is restricted because of their large size, cost and need for high optical pump powers5. Here we demonstrate a monocrystalline titanium:sapphire-on-insulator (Ti:SaOI) photonics platform that enables dramatic miniaturization, cost reduction and scalability of Ti:sapphire technology. First, through the fabrication of low-loss whispering-gallery-mode resonators, we realize a Ti:sapphire laser operating with an ultralow, sub-milliwatt lasing threshold. Then, through orders-of-magnitude improvement in mode confinement in Ti:SaOI waveguides, we realize an integrated solid-state (that is, non-semiconductor) optical amplifier operating below 1 μm. We demonstrate unprecedented distortion-free amplification of picosecond pulses to peak powers reaching 1.0 kW. Finally, we demonstrate a tunable integrated Ti:sapphire laser, which can be pumped with low-cost, miniature, off-the-shelf green laser diodes. This opens the doors to new modalities of Ti:sapphire lasers, such as massively scalable Ti:sapphire laser-array systems for several applications. As a proof-of-concept demonstration, we use a Ti:SaOI laser array as the sole optical control for a cavity quantum electrodynamics experiment with artificial atoms in silicon carbide6. This work is a key step towards the democratization of Ti:sapphire technology through a three-orders-of-magnitude reduction in cost and footprint and introduces solid-state broadband amplification of sub-micron wavelength light.

Unraveling the cation dependent carrier cooling and transient mobility in lead-free A3Sb2I9 perovskites.

Lead halide perovskites (LHPs) have gained prominence for their exceptional photophysical properties, holding promise for applications in high-end optoelectronic devices. However, the presence of lead is one of the major obstacles to the commercialization of LHPs in the field of photovoltaics. To address this, researchers have explored environment friendly lead-free perovskite solar cells by investigating non-toxic perovskite materials. This study explores the enhancement of photophysical properties through chemical engineering, specifically cation exchange, focusing on the crucial photophysical process of hot carrier cooling. Employing femtosecond transient absorption spectroscopy and optical pump terahertz probe spectroscopy, we have probed the carrier relaxation dynamics in A3Sb2I9 with cesium and rubidium cations. This study unravels that the carrier relaxation is found to be slower in Rb3Sb2I9; along with this, the transient mobility decay is found to be retarded. Overall, this study suggests that an antimony-based Rb3Sb2I9 perovskite could be a substantial lead-free perovskite in photovoltaics. These findings provide valuable insights into cation engineering strategies, aiming to improve the overall performance of lead-free-based photovoltaic devices.

One-Step Preparation Method and Rapid Detection Implementation Scheme for Simple Magnetic Tagging Materials

With the widespread application of tagging materials, existing chemical tagging materials exhibit limitations in stability and detection under field conditions. This study introduces a novel magnetic detection scheme. Hydrophilic material-modified Fe3O4 nanoparticles (COOH-PEG@Fe3O4 NPs) were synthesized using the co-precipitation technique. The content of Fe3O4 nanoparticles in the magnetic tagging liquid can reach up to 10 wt% and remain stable in an aqueous phase system for seven days. This research details the preparation process, the characterization methods (IR, 1HNMR, EDX, XRD, SEM, TEM, VSM, DLS), and the performance effects of the materials in magnetic tagging. Experimental results indicate that COOH-PEG@Fe3O4 NPs exhibit high remanence intensity (Br = 1.75 emu/g) and considerable stability, making it possible to quickly detect tagged liquids in the field using portable flux meters and optical pump magnetometers. This study provides new insights into the design and application of magnetic tagging materials, making it particularly suitable for long-term tagging and convenient detection in field scenarios.

Unraveling Defect-Mediated Enhancement of Transient Photoconductivity and Slower Carrier's Mobility Decay in Cu-Doped Cs2AgBiBr6 Nanocrystals Using Ultrafast Pump-Probe Spectroscopy.

Lead-free double perovskite nanocrystals (A2B'(III)B″(I)X6 NCs) address the instability and toxicity concerns of lead-based counterparts, but their device performance is limited by subpar absorption and unexplored carrier dynamics. Impurity ion doping offers a route to tune electrical conductivity and charge carrier transport. Herein, we synthesized Cu-doped Cs2AgBiBr6 (CABB) nanocrystals using a hot-injection approach and investigated the charge carrier's dynamics through ultrafast pump-probe spectroscopy. Copper introduction into the CABB lattice enhanced absorption in the near-infrared region and introduced sub-band gap defect states in CABB NCs. The transient absorption study revealed a faster bleach decay with increased copper doping, as a result of charge transfer from the conduction band to copper defect states. Also, an optical pump terahertz probe study displays higher photoconductivity and mobility in Cu-doped CABB NCs. Slower mobility decay in Cu-doped systems was attributed to the charge carrier's entrapment at the defect state. These findings suggest that copper-doped CABB is a superior contender for optoelectronic applications over conventional CABB.

Design of optically pumped ultrahigh-performance terahertz sensors based on graphene metamaterials

The surface conductivity of graphene can be precisely adjusted to approach the sigma-near-zero (SNZ) point by manipulating the quasi-Fermi level via optical pumping. This capability holds great promise for advanced graphene metamaterials-based terahertz (THz) sensors. In this study, we present a rational approach for designing two distinct types of patterned graphene THz sensors, each tailored to specific requirements regarding the quasi-Fermi level, resonance frequency, and Q-factor. The first sensor type operates in transmission mode and is well-suited for analytes with refractive indices ranging from 1 to 2. With a fixed analyte thickness of 40 nm, it achieves a frequency sensitivity of 1.036 THz/RIU, a Q-factor between 230 and 360, and a figure of merit (FOM) ranging from 51/RIU to 74/RIU. The second sensor type operates in reflection mode and is optimized for detecting biomolecules with refractive indices between 1.5 and 1.7. It exhibits a significant frequency shift of approximately 0.16 THz and a reflectance variation as high as 0.941 when the bio-analyte thickness is 100 nm. Numerical simulations of the sensing performances confirm the potential of these designed sensors for applications in detecting thin dielectric films and biosensing.

Low-threshold lasing behavior assisted by the asymmetric grating profile in the guided-mode resonance structure

We present a nanoscale laser based on an asymmetric guided-mode resonance (AGMR) structure. The AGMR creates hybrid resonant modes, which consist of the newly generated quasi-bound states in the continuum (quasi-BICs) and the intrinsic GMR mode. By modifying the structural parameters, the GMR and quasi-BICs modes can be matched with the pump and emission wavelengths of the gain medium, respectively. Therefore, high-intensity near fields of the GMR as the resonant optical pumping mode and high quality (Q) factor of the quasi-BICs as the resonant-emitting mode jointly contribute to the low-threshold lasing behavior. The finite-difference time-domain method is used to analyze the lasing characteristics, and a threshold of 14.2 μJ/cm2 is obtained, which is approximately ten times lower than that of a single-coupled mode laser. By adjusting the asymmetry parameters and fill factor of the grating, the threshold can be further reduced to 8.9 μJ/cm2. Additionally, we have also studied the feasibility of the AGMR structure by adjusting the simulation boundary conditions from periodic to perfectly matched layer to simulate a finite-sized structure. The findings provide a new way to excite hybrid modes, opening up possibilities for applications that demand highly confined fields and high Q-factors.

A polarized 3He system based on metastability-exchange optical pumping

A polarized 3He system based on metastability-exchange optical pumping

Ultra-high spin emission from antiferromagnetic FeRh

An antiferromagnet emits spin currents when time-reversal symmetry is broken. This is typically achieved by applying an external magnetic field below and above the spin-flop transition or by optical pumping. In this work we apply optical pump-THz emission spectroscopy to study picosecond spin pumping from metallic FeRh as a function of temperature. Intriguingly we find that in the low-temperature antiferromagnetic phase the laser pulse induces a large and coherent spin pumping, while not crossing into the ferromagnetic phase. With temperature and magnetic field dependent measurements combined with atomistic spin dynamics simulations we show that the antiferromagnetic spin-lattice is destabilised by the combined action of optical pumping and picosecond spin-biasing by the conduction electron population, which results in spin accumulation. We propose that the amplitude of the effect is inherent to the nature of FeRh, particularly the Rh atoms and their high spin susceptibility. We believe that the principles shown here could be used to produce more effective spin current emitters. Our results also corroborate the work of others showing that the magnetic phase transition begins on a very fast picosecond timescale, but this timescale is often hidden by measurements which are confounded by the slower domain dynamics.

Near-field optomechanical transduction enhanced by Raman gain.

Raman-gain-enhanced near-field optomechanical transduction between a movable optical cavity and SiN-membrane resonator is demonstrated. The Raman gain compensates for the intrinsic loss of the cavity and amplifies the optomechanical transduction, through which the membrane vibration is sensed using a high-Q whispering-gallery-mode optical cavity evanescently. The optical Q of the cavity resonance is improved with respect to the optical pump power, which results in an increase in the optomechanically transduced vibration signals of the mechanical resonator. Our near-field optomechanical coupling approach with optical gain realizes highly sensitive displacement measurement in nano- and micro-mechanical resonators consisting of arbitrary materials and structures.

Observation of a Picosecond Light-Induced Spin Transition in Polymeric Nanorods.

Spin transition (ST) materials are attractive for developing photoswitchable devices, but their slow material transformations limit device applications. Size reduction could enable faster switching, but the photoinduced dynamics at the nanoscale remains poorly understood. Here, we report a femtosecond optical pump multimodal X-ray probe study of polymeric nanorods. Simultaneously tracking the ST order parameter with X-ray emission spectroscopy and structure with X-ray diffraction, we observe photodoping of the low-spin-lattice within ∼150 fs. Above a ∼16% photodoping threshold, the transition to the high-spin phase occurs following an incubation period assigned to vibrational energy redistribution within the nanorods activating the molecular spin switching. Above ∼60% photodoping, the incubation period disappears, and the transition completes within ∼50 ps, preceded by the elastic nanorod expansion in response to the photodoping. These results support the feasibility of ST material-based GHz optical switching applications.

Hyperpolarization of Nuclei by the Method of Spin-Exchange Optical Pumping

Hyperpolarization of Nuclei by the Method of Spin-Exchange Optical Pumping

Velocimetry of GHz elastic surface waves in quartz and fused silica based on full-field imaging of pump–probe reflectometry

This study reports an imaging method for gigahertz surface acoustic waves in transparent layers using infrared subpicosecond laser pulses in the ablation regime and an optical pump–probe technique. The reflectivity modulations due to the photoelastic effect of generated multimodal surface acoustic waves were imaged by an sCMOS camera illuminated by the time-delayed, frequency-doubled probe pulses. Moving the delay time between 6.0nsto11.5ns, image stacks of wave field propagation were created.Two representative samples were investigated: wafers of isotropic fused silica and anisotropic x-cut quartz. Rayleigh (SAW) and longitudinal dominant high-velocity pseudo-surface acoustic wave (HVPSAW) modes could be observed and tracked along a circular grid around the excitation center, allowing the extraction of angular profiles of the propagation velocity. In quartz, the folding of a PSAW was observed. A finite element simulation was developed to predict the measurement results. The simulation and measurement were in good agreement with a relative error of 2% to 5%.These results show the potential for fast and full-field imaging of laser-generated ultrasonic surface wave modes, which can be utilized for the characterization of thin transparent samples such as semiconductor wafers or optical crystals in the gigahertz frequency range.

Distributed Feedback Lasing in Thermally Imprinted Phase‐Stabilized CsPbI3 Thin Films

AbstractAll‐inorganic cesium lead halide perovskites (CsPbX3, with X = I, Br, Cl) are of great interest for light‐emitting diodes and lasers, as they promise improved thermal stability compared to their organic–inorganic analogues. However, among this family of materials, CsPbI3 shows a detrimental phase instability that causes the perovskite to convert to a thermodynamically preferred non‐perovskite phase (yellow phase) at room temperature. In fact, reports on lasers using thin films of CsPbI3 as gain medium are missing, as of yet. Here, the first distributed feedback (DFB) lasers based on CsPbI3 thin films are presented with a resonator directly patterned into the perovskite by thermal nanoimprint. This breakthrough is unlocked by the additive polyvinyl pyrrolidone (PVP), that affords the formation of perovskite layers consisting of phase stable γ‐CsPbI3 nanocrystals, that are even preserved during thermal imprint at 170 °C. The DFB lasers show a low lasing threshold of 45 µJ cm−2 at room temperature under optical pumping and a tunable emission in the deep red spectral region between 714.1 to 723.4 nm. It is anticipated that the findings of this work will have a broad relevance for future electrically driven perovskite lasers and for light‐emitting diodes based on CsPbI3 as active medium.

Structural pathways for ultrafast melting of optically excited thin polycrystalline Palladium films

Due to its extremely short timescale, the non-equilibrium melting of metals is exceptionally difficult to probe experimentally. The knowledge of melting mechanisms is thus based mainly on the results of theoretical predictions. This work reports on the investigation of ultrafast melting of thin polycrystalline Pd films studied by optical laser pump – X-ray free-electron laser probe experiments and molecular-dynamics simulations. By acquiring X-ray diffraction snapshots with sub-picosecond resolution, we capture the sample's atomic structure during its transition from the crystalline to the liquid state. Bridging the timescales of experiments and simulations allows us to formulate a realistic microscopic picture of the crystal-liquid transition. According to the experimental data, the melting process gradually accelerates with the increasing density of deposited energy. The molecular dynamics simulations reveal that the transition mechanism progressively varies from heterogeneous, initiated inside the material at structurally disordered grain boundaries, to homogenous, proceeding catastrophically in the crystal volume on a picosecond timescale comparable to that of electron-phonon coupling. We demonstrate that the existing models of strongly non-equilibrium melting, developed for systems with relatively weak electron-phonon coupling, remain valid even for ultrafast heating rates achieved in femtosecond laser-excited Pd. Furthermore, we highlight the role of pre-existing and transiently generated crystal defects in the transition to the liquid state.

Spin injection enhancement in CW VECSEL at room temperature using push-pull optical pumping.

We report the enhancement of spin injection efficiency in an external-cavity VCSEL based on a non-resonant pumping coupled with a polarized optical resonant illumination. This double pumping scheme allows both the injection of spin polarized electrons in the conduction band and the selection of the spin orientation for the electron/hole recombination laser process. Experimentally, a flip of the polarization state of the laser is achieved with an ellipticity of +31° (spin down) and -33° (spin up), so an increase of about 50% of the ellipticity is achieved in comparison to an optical non-resonant pumping alone.

Realization of robust quantum noise characterization in the presence of coherent errors

Complex quantum systems and their various applications are susceptible to noise of coherent and incoherent nature. Characterization of noise and its sources is an open, key challenge in quantum technology applications, especially in terms of distinguishing between inherent incoherent noise and systematic coherent errors. In this paper, we study a scheme of repeated sequential measurements that enables the characterization of incoherent errors by reducing the effects of coherent errors. We demonstrate this approach using a coherently controlled nitrogen vacancy in diamond, coupled to both a natural nuclear spin bath (non-Markovian) and to experimentally controlled relaxation through an optical pumping process (nearly Markovian). Our results show mitigation of coherent errors both for Markovian and non-Markovian incoherent noise profiles. We apply this scheme to the estimation of the dephasing time (T2*) due to incoherent noise. We observe an improved robustness against coherent errors in the estimation of dephasing time (T2*) compared to the standard (Ramsey) measurement.

Manipulating optical absorption and polarization using microwave control in an atomic vapor

The multiplicity of atomic states (and the transitions between them) offer an innate, coherent platform through which microwave and optical fields effectively interact. In an atomic vapor near room temperature, we combine optical and microwave fields to generate a macroscopic internal angular momentum among the atoms—an atomic polarization—at an arbitrary angle with respect to the optical (laser) beam. This geometric freedom enables microwave control over photonic degrees of freedom, which we use in two demonstrations: using microwave-assisted optical pumping, we can rotate linear polarization through several degrees, and we can control the absorption for specific transitions and polarizations, which has applications for microwave-to-optical transduction.

Architecture for Surface-Emitting Lasers with On-Demand Lasing Wavelength by Nanowire Optical Cavities.

Despite the importance and exciting progress of surface-emitting (SE) semiconductor lasers, we have limited choices of lasing wavelength even today. From an application viewpoint, it is desirable to have an architecture that can allow SE lasing in a wide spectral range, based on the need of applications. Herein, we demonstrate a path for SE lasers with lasing wavelength on demand by exploiting III-nitride nanowire optical cavities formed by low-temperature selective area epitaxy (SAE), combined with fine-tuning of substrate patterns and photonic bands. Moreover, in this study, we focus on the device demonstration in the ultraviolet (UV) spectral range, considering the severe lag in developing SE lasers in the UV wavelength range compared to longer wavelengths, e.g., near-infrared (NIR), as well as the potential applications enabled by UV lasers such as solar blind optical wireless communications. Ultralow threshold wavelength-tunable SE UV lasing is achieved by optical pumping. Moreover, SE UV lasing under direct electric current injection is also achieved. This study not only represents an important step in the journey of SE UV laser development but, more importantly, it lays the ground for SE lasers with lasing wavelength on demand, broadly from NIR to UV.

10-mJ 300-fs 1-kHz cryogenically cooled Yb:CaF2 regenerative amplifier

In this paper, we report on a cw-pumped cryogenically cooled Yb:CaF2 laser crystal regenerative amplifier that can produce >10.3 mJ, <285 fs laser pulses at 1034-nm and repetition rate of 1-kHz. We achieve record high optical pump to optical amplified compressed output efficiency at >14%. Using a symmetric cavity design to compensate thermal lensing effect, we were able to achieve excellent beam quality with measured M2 at 1.19 and 1.16 at horizontal and vertical directions, respectively.

Perovskite Quantum Dots Lasing in Double-Heterostructure through Energy Transfer.

Planar double heterostructures were initially investigated and have been successfully applied in III-V semiconductor lasers due to their excellent roles in confining both the photons and carriers. Here, we design and fabricate a (PEA)2Csn-1PbnX3n+1 (quasi-2D)/CsPbBr3 QD/quasi-2D double-heterostructure sandwiched in a 3/2 λ DBR microcavity, and then demonstrate a single-mode pure-green lasing with a threshold of 53.7 μJ/cm2 under nanosecond-pulsed optical pumping. The thresholds of these heterostructure devices decrease statistically by about 50% compared to the control group with no energy donor layers, PMMA/QD/PMMA in an identical microcavity. We show that there is efficient energy transfer from the barrier regions of the quasi-2D phases to the QD layer by transient absorption and luminescence lifetime spectra and that such energy transfer leads to marked threshold reduction. This work indicates that the double-heterostructure configurations should play a significant role in the future perovskite electrically pumped laser.