Two-photon Pumping Research Articles

Two-photon pumped random lasing in MAPbBr3 with directional output for far-field applications

We investigate the random lasing properties of polycrystalline MAPbBr3 grown in a hollow fiber. Coupling of the random lasing on the inner wall of the hollow fiber into the annular cylinder and guided by the inner surface of hollow cavity enable directional output of the random lasing emission. The polycrystalline MAPbBr3 was grown by the capillary effect, when one end of the hollow fiber was dipped into the precursor solution. A two-photon pumping scheme was employed, where femtosecond pulses centered at about 800 nm was focused onto the MAPbBr3 polycrystals through the side wall of the hollow fiber. Random lasing was achieved due to the strong optical scattering by the interfaces within the polycrystals on the inner wall of the hollow fiber. The random lasing output was re-collimated into a roughly parallel beam with a circular transverse mode, which favors far-field applications of random lasers. Two-photon pumping enables larger penetration depth and larger excitation volume than single-photon pumping, so that strong lasing spot can also be observed in the center area of the output laser beam.

Enhancing quantum synchronization through homodyne measurement, noise, and squeezing.

Quantum synchronization has been a central topic in quantum nonlinear dynamics. Despite the rapid development in this field, very few have studied how to efficiently boost synchronization. Homodyne measurement emerges as one of the successful candidates for this task but preferably in the semiclassical regime. In our work, we focus on the phase synchronization of a harmonic-driven quantum Stuart-Landau oscillator and show that the enhancement induced by homodyne measurement persists into the quantum regime. Interestingly, optimal two-photon damping rates exist when the oscillator and driving are at resonance and with a small single-photon damping rate. We also report noise-induced enhancement in quantum synchronization when the single-photon damping rate is sufficiently large. Apart from these results, we discover that adding a squeezing Hamiltonian can further boost synchronization, especially in the semiclassical regime. Furthermore, the addition of squeezing causes the optimal two-photon pumping rates to shift and converge.

Amplified Spontaneous Emission and Lasing from Zn-Processed AgIn5S8 Core/Shell Quantum Dots

I-III-VI ternary quantum dots (QDs) have emerged as favorable alternatives to the toxic II-VI QDs for optoelectronic and biological applications. However, their use as optical gain media for microlasers is still limited by a low fluorescence efficiency. Here, we demonstrate amplified spontaneous emission (ASE) and lasing from colloidal QDs of Zn-processed AgIn5S8 (AIS) for the first time. The passivation treatment on the AIS QDs yields a 3.4-fold enhancement of fluorescence quantum efficiency and a 30% increase in the two-photon absorption cross section. ASE is achieved from the AIS/ZnS core/shell QD films under both one- and two-photon pumping with a threshold fluence of ∼84.5 μJ/cm2 and 3.1 mJ/cm2, respectively. These thresholds are comparable to the best optical gain performance of Cd based-QDs reported in the literature. Moreover, we demonstrate a facile whispering-gallery-mode microlaser of the core/shell QDs with a lasing threshold of ∼233 μJ/cm2. The passivated AIS QDs can be promising optical gain media for photonic applications.

Two-photon IR pumped UV–Vis transient absorption spectroscopy of Dirac fermions in the topological insulator Bi2Se3

It is often taken for granted that in pump-probe experiments on the topological insulator (TI) Bi2Se3 using IR pumping with a commercial Ti:sapphire laser [∼800 nm (1.55 eV photon energy)], the electrons are excited in the one-photon absorption regime, even when pumped with absorbed fluences in the mJ cm−2 range. Here, using UV–Vis transient absorption (TA) spectroscopy, we show that even at low-power Infrared (IR) pumping with absorbed fluences in the μJ cm−2 range, the TA spectra of the TI Bi2Se3 extend across a part of the UV and the entire visible region. This observation suggests unambiguously that the two-photon pumping regime accompanies the usual one-photon pumping regime even at low laser powers applied. We attribute the high efficiency of two-photon pumping to the giant nonlinearity of Dirac fermions in the Dirac surface states (SS). On the contrary, one-photon pumping is associated with the excitation of bound valence electrons in the bulk into the conduction band. Two mechanisms of absorption bleaching were also revealed since they manifest themselves in different spectral regions of probing and cause the appearance of three different relaxation dynamics. These two mechanisms were attributed to the filling of the phase-space in the Dirac SS and bulk states, followed by the corresponding Pauli blocking.

Dissipative Phase Transition in Systems with Two-Photon Drive and Nonlinear Dissipation near the Critical Point.

In this paper, we examine dissipative phase transition (DPT) near the critical point for a system with two-photon driving and nonlinear dissipations. The proposed mean-field theory, which explicitly takes into account quantum fluctuations, allowed us to describe properly the evolutionary dynamics of the system and to demonstrate new effects in its steady-state. We show that the presence of quantum fluctuations leads to a power-law dependence of the anomalous average at the phase transition point, with which the critical exponent is associated. Also, we investigate the effect of the quantum fluctuations on the critical point renormalization and demonstrate the existence of a two-photon pump “threshold”. It is noteworthy that the obtained results are in a good agreement with the numerical simulations.

Fast generation of cat states in Kerr nonlinear resonators via optimal adiabatic control

Macroscopic cat states have been widely studied to illustrate fundamental principles of quantum physics as well as their applications in quantum information processing. In this paper, we propose a quantum speed-up method for the creation of cat states in a Kerr nonlinear resonator (KNR) via optimal adiabatic control. By simultaneously adiabatic tuning the cavity-field detuning and driving field strength, the width of the minimum energy gap between the target trajectory and non-adiabatic trajectory can be widened, which allows us to accelerate the evolution along the adiabatic path. Compared with the previous proposal, preparing cat states only by controlling two-photon pumping strength, our method can prepare the target state with a shorter time, a high-fidelity and a large non-classical volume. It is worth noting that the cat state prepared here is also robust against single-photon loss. Moreover, when we consider the KNR with a large initial detuning, our proposal will create a large-size cat state successfully. This proposal for preparing cat states can be implemented in superconducting quantum circuits, which provides a quantum state resource for quantum information encoding and fault-tolerant quantum computing.

Red-Shifted Excitation and Two-Photon Pumping of Biointegrated GaInP/AlGaInP Quantum Well Microlasers.

Biointegrated intracellular microlasers have emerged as an attractive and versatile tool in biophotonics. Different inorganic semiconductor materials have been used for the fabrication of such biocompatible microlasers but often operate at visible wavelengths ill-suited for imaging through tissue. Here, we report on whispering gallery mode microdisk lasers made from a range of GaInP/AlGaInP multi-quantum well structures with compositions tailored to red-shifted excitation and emission. The selected semiconductor alloys show minimal toxicity and allow the fabrication of lasers with stable single-mode emission in the NIR (675–720 nm) and sub-pJ thresholds. The microlasers operate in the first therapeutic window under direct excitation by a conventional diode laser and can also be pumped in the second therapeutic window using two-photon excitation at pulse energies compatible with standard multiphoton microscopy. Stable performance is observed under cell culturing conditions for 5 days without any device encapsulation. With their bio-optimized spectral characteristics, low lasing threshold, and compatibility with two-photon pumping, AlGaInP-based microlasers are ideally suited for novel cell tagging and in vivo sensing applications.

Two-photon absorption and stimulated emission in poly-crystalline Zinc Selenide with femtosecond laser excitation

The optical nonlinearity in polycrystalline zinc selenide (ZnSe), excited with 775 nm, 1 kHz femtosecond laser pulses was investigated via the nonlinear transmission with material thickness and the Z scan technique. The measured two photon absorption coefficient <em>β</em> was intensity dependent, inferring that reverse saturated absorption (RSA) is also relevant during high intensity excitation in ZnSe. At low peak intensity <em>I</em> &lt; 5 GW cm^–2, we find <em>β</em> = 3.5 cm GW^–1 at 775 nm. The spectral properties of the broad blueish two-photon induced fluorescence (460 nm-500 nm) was studied, displaying self-absorption near the band edge while the upper state lifetime was measured to be τ_e ~ 3.3 ns. Stimulated emission was observed when pumping a 0.5 mm thick polycrystalline ZnSe sample within an optical cavity, confirmed by significant line narrowing from Δ<em>λ</em> = 11 nm (cavity blocked) to Δ<em>λ</em> = 2.8 nm at peak wavelength <em>λ</em>_p = 475 nm while the upper state lifetime also decreased. These results suggest that with more optimum pumping conditions and crystal cooling, polycrystalline ZnSe might reach lasing threshold via two-photon pumping at <em>λ</em> = 775 nm.

Visualizing coherent vibrational motion in the molecular iodine B3Π0+u state using ultrafast XUV transient-absorption spectroscopy

Attosecond probing of core-level electronic transitions in molecules provides a sensitive tool for real-time observation of chemical dynamics. Here, we employ ultrafast extreme-ultraviolet (XUV) transient-absorption spectroscopy to investigate the excited state electronic and nuclear dynamics in a prototype molecule, ${\mathrm{I}}_{2}$. A few-femtosecond visible pump pulse is employed to excite the ${\mathrm{I}}_{2}$ molecule and an attosecond XUV pulse is used to probe the dynamics through iodine-$4d$ core-to-valence transitions. A highly extended vibrational wave packet $({\ensuremath{\nu}}^{\ensuremath{'}}=10--50,\phantom{\rule{0.28em}{0ex}}{\ensuremath{\nu}}_{max}^{\ensuremath{'}}=25)$ is prepared by one-photon absorption in the valence excited $B\phantom{\rule{0.28em}{0ex}}{}^{3}{\mathrm{\ensuremath{\Pi}}}_{{{0}^{+}}_{\mathrm{u}}}$ state of ${\mathrm{I}}_{2}$ and its motion is directly mapped due to the strong shift of the XUV core-level transition with internuclear separation. Through the imaging of this vibrational motion, we directly reconstruct the transition energy between the valence and the core-excited states as a function of internuclear distance. Besides single-photon dynamics, distinct direct dissociation pathways arising from two-photon pump absorption are also revealed.

Two photon pumped nanowire laser based on all inorganic perovskite with high exciton binding energy grown by physical vapor deposition

Cesium lead halide (CsPbBr3) perovskite nanomaterials exhibit attractive optical properties, particularly in higher nonlinear optical effects and larger multiphoton absorption efficiency, compared with conventional semiconductors. The unique feature of stable lasing action under photon pumping conditions grants such materials great potential in photonics. Herein, through an in-depth study of the growing mechanism, all-inorganic perovskite nanomaterials with a high crystalline quality and tunable morphologies were synthesized, by a modified physical vapor deposition procedure. The prepared nanowire laser not only presents a high-performance laser output under single-photon pumping conditions, but also maintains decent behavior under two-photon pumping conditions. Importantly, the temperature-dependent fluorescence spectroscopy test of the nanowires reveals that the high exciton binding energy, twice as large as the thermal disturbance at room temperature, is the dominant reason for maintaining stable lasing under high energy density injection conditions.

Decay of a laser beam under stimulated temperature scattering in toluene as a result of two-photon pump absorption and nonsteady-state laser pulse interaction with matter

The decay of the pump-beam spatial structure under conditions of stimulated temperature scattering of a pulsed laser beam in toluene as a result of two-photon absorption of pump radiation and time-dependent interaction of a laser pulse with a medium is considered.

Second harmonic generation in colloidal CdSe/CdS nanoplatelets

In this Letter, we report the second harmonic generation (SHG) in a colloidal solution of CdSe/CdS nanoplatelets (NPLs) in the case of two-photon excitation in the region of exciton transition from the light holes sub-band to the conduction sub-band (549 nm, 1lh-1e) by femtosecond laser pulses (1064 nm, 100 kHz). Discovery of the SHG in colloidal solutions of NPLs opens up new perspectives for their use as biomarkers or for optical imaging, since in contrast to two-photon photoluminescence the SHG can increase both spectral and temporal resolution by several orders of magnitude. The SHG is also extremely important to consider when designing two-photon pumping lasers.

Remote Lasing in Humid Air from Atomic Hydrogen

Over the last few years, air lasing has emerged as an attractive topic in standoff detection research. However, existing approaches have relied on the major species of air as the gain medium. This work presents the first experimental demonstration of an air laser based on water vapor, a minor constituent of air. The approach relies on photodissociation of water vapor molecules followed by two-photon pumping of the constituent hydrogen atoms to produce lasing on the well-known Balmer-alpha line. This hydrogen laser is characterized in both the forward as well as return direction, and this paper discusses the effect of some parameters, including the presence and type of buffer gas, as well as the pump beam focusing. It is found that most of these results can be explained in terms of their influence on the gain of the stimulated emission process. This method can be potentially applied to other hydrogen-containing molecules and offers a promising approach for standoff detection of trace species.

Stable and low-threshold whispering-gallery-mode lasing from modified CsPbBr3 perovskite quantum dots@SiO2 sphere

Miniaturized solid-state lasers have obtained great development for their outstanding properties. Among the optical gain materials discovered so far, CsPbBr3 perovskite quantum dots (QDs) have been recognized as one of the most promising candidates due to the direct bandgap, narrow emission linewidth and high quantum yield. Herein, we report the fabrication of whispering-gallery-mode (WGM) lasers from the unmodified CsPbBr3 QDs and the 2-hexyldecanoic acid (DA) modified CsPbBr3 QDs. Thanks to the strong binding energy between DA ligand and QDs, the modified CsPbBr3 QDs show much better optical properties than that of the common CsPbBr3 QDs. In comparison with the unmodified CsPbBr3 QDs, the lasing threshold of WGM lasers obtained from the modified CsPbBr3 QDs is decreased from 126.81 and 261.97 μJ/cm2 to 5.47 and 88.49 μJ/cm2 under one-photon and two-photon pump excitation, respectively. Besides, WGM lasers based on the modified CsPbBr3 QDs demonstrate higher stability than that of common CsPbBr3 QDs WGM lasers under the same continuously pumping over ten hours. This work may not only enrich the application of the ligand modified CsPbBr3 QDs but also provide a strategy for the facile design of low-threshold WGM lasers.

Two-photon pumped spaser based on the CdS/ZnS core/shell quantum dot–mesoporous silica–metal structure

The spaser (a plasmonic nanolaser) has rapidly advanced as a subwavelength light source candidate. Herein, we introduce a spaser based on a quantum-dot, mesoporous-oxide, and metal structure from top to bottom consisting of CdS/ZnS core/shell quantum dots, a mesoporous silica film (MSF), and an Au film, respectively. Two-photon pumping using femtosecond laser pulses at 800 nm creates amplified spontaneous emission at approximately 451 nm. The advantages of MSF as a dielectric gap layer are examined through numerical simulations. Measuring the dependence of the luminescence intensity on the average pump power confirms the occurrence of two-photon up-conversion luminescence.

Two-photon-pumped high-quality, single-mode vertical cavity lasing based on perovskite monocrystalline films

Single-mode microlasers are of crucial importance for high-performance integrated photonic devices. However, it still remains a significant challenge to achieve single-mode microlasers conveniently. In this work, we propose a strategy to realize high-quality, single-mode vertical-cavity surface-emitting lasers (VCSELs) based on hybrid perovskite monocrystalline films. Under two-photon pump, the VCSEL exhibits excellent performances with a remarkable low threshold of ~421 μJ/cm2, a high quality factor (Q factor) of ~1286 and a small divergence angle of ~0.5°. Importantly, single-mode lasing with a good spatial coherence can be conveniently achieved with the VCSEL configuration, which significantly reduces the complexity for fabricating high-quality single-mode microlasers. In addition, switchable VCSEL can be realized by taking advantage of the anisotropic two-photon absorption of the hybrid perovskites. The single-mode vertical-cavity emission, excellent lasing performances, frequency up-conversion ability and switchable property will provide a versatile platform for high-performance nanosources and multifunctional integrated optoelectronic devices.

Detection of atomic oxygen in a plasma-assisted flame via a backward lasing technique.

In this Letter, we have investigated 845nm lasing generation in atomic oxygen, present in a lean methane-air flame, using two-photon pumping with femtosecond 226nm laser pulses, particularly focusing on the impact of nanosecond repetitively pulsed glow discharges forcing on the backward lasing signal. Characterizations of the backward lasing pulse, in terms of its spectrum, beam profile, pump pulse energy dependence, and divergence, were conducted to establish the presence of lasing. With plasma forcing of the flame, the backward lasing signal was observed to be enhanced significantly, ∼50%. The vertical concentration profile of atomic oxygen was revealed by measuring the backward lasing signal strength as a function of height in the flame. The results are qualitatively consistent with results obtained with two-dimensional femtosecond two-photon-absorption laser-induced fluorescence, suggesting that the backward lasing technique can be a useful tool for studies of plasma-assisted combustion processes, particularly in geometries requiring single-ended standoff detection.

Threshold photodissociation dynamics of NO2 studied by time-resolved cold target recoil ion momentum spectroscopy.

We study the near-threshold photodissociation dynamics of NO2 by a kinematically complete femtosecond pump-probe scheme using a cold target recoil ion momentum spectrometer. We excite NO2 to the optically bright Ã2B2 state with a 400 nm pulse and probe the ensuing dynamics via strong field single and double ionization with a 25 fs, 800 nm pulse. The pump spectrum spans the NO(X2Π) + O(3P) dissociation channel threshold, and therefore, following internal conversion, excited NO2 is energetically prepared both "above threshold" (dissociating) and "below threshold" (nondissociating). Experimentally, we can clearly discriminate a weak two-photon pump channel from the dominant single-photon data. In the single ionization channel, we observe NO+ fragments with nonzero momentum at 200 fs delay and an increasing yield of NO+ fragments with near-zero momentum at 3.0 ps delay. For double ionization events, we observe a time-varying Coulombic kinetic energy release between the NO+ and O+ fragments impulsively created from the evolving "hot" neutral ground state. Supported by classical trajectory calculations, we assign the decreasing Coulombic kinetic energy release at longer time delays to the increasing average NO-O distances in the ground electronic state during its large amplitude phase space evolution toward free products. The time-resolved kinetic energy release in the double ionization channel probes the large amplitude ground state evolution from a strongly coupled "inner region" to a loosely coupled "outer region" where one O atom is on average much further away from the NO. Both the time evolution of the kinetic energy release and the NO+ angular distributions support our assignments.

Analytical study of the spiky feature in a two-photon driven lossy ladder system

There has been an experimental report (Traverso et al 2012 Proc. Natl Acad. Sci. USA 109 15185) that oxygen lasing in ambient air exhibits a spiky feature. We theoretically explore a ladder-type three-level atomic system driven by a two-photon resonant pump pulse in a lossy medium, which corresponds to that oxygen experiment. We study the Maxwell–Bloch equations both numerically and analytically and discover that a long pump field brings competition between two mechanisms of coherent pumping and coherent emission, leading to the spiky emission, which cannot be produced using a short pump. The results indicate that atomic coherence occurs in the experiment. Our study provides a clear understanding of the oxygen experiment using a nanosecond pump laser and could lead to the potential application of this oxygen lasing in future experiments.

Stimulated emission from CsPbBr3 quantum dot nanoglass

We report on a high-temperature vapor drop-casting technique used to fabricate a chemically stable nanomaterial‒CsPbBr3 quantum dot nanoglass that exhibits stable photoluminescence and stimulated emission properties. Such nanomaterial is comprised of two material domains: nano-fractured glassy-phase matrix and embedded CsPbBr3 quantum dots. The nanoglass is compatible with various pump sources to attain a low-threshold stimulated emission via either linear or nonlinear pump schemes. We demonstrate that the pump threshold could be remarkably reduced when the pump wavelength shifts from the peak position of the photoluminescence excitation spectrum to the photoluminescence peak. In addition, the lowest pump threshold achieved in the two-photon pump regime is comparable to that ever-reported lowest value using colloidal CsPbBr3 quantum dots. Cooperative contributions from local disorders on both of the pump beam and the emitted light are proposed to account for the observed stimulated emission properties.