Three-level Laser Research Articles

The Noise Effect of Vacuum Reservoir on the Dynamics of Three-Level Laser Pumped by Coherent Light

We have investigated the effects of vacuum reservoir noise on the photon statistics and quadrature squeezing of light generated by a three-level laser pumped by coherent light and coupled to a vacuum reservoir via a single-port mirror. We have found that the effect of the vacuum reservoir noise is to increase the photon number variance and to decrease the quadrature squeezing. However, the vacuum reservoir noise has no effect on the mean photon number.

Spontaneous Emission by Three-level Atoms Pumped by Electron Bombardment

In this paper we have studied the statistical and squeezing properties of the cavity light generated by a three-level laser. In this quantum optical system, N three-level atoms available in an open cavity, coupled to a two-mode vacuum reservoir, are pumped to the top level by means of electron bombardment at constant rate. We have considered the case in which the three-level atoms and the cavity modes interact with the two-mode vacuum reservoir. We have carried out our analysis by putting the noise operators associated with the vacuum reservoir in normal order. Applying the solutions of the equations of evolution for the expectation values of the atomic operators and the quantum Langevin equations for the cavity mode operators, we have calculated the mean and variance of the photon number as well as the quadrature squeezing for the cavity light. In addition, we have shown that the presence of the spontaneous emission process leads to a decrease in the mean and variance of the photon number. We have observed that the two-mode cavity light is in a squeezed state and the squeezing occurs in the minus quadrature. The maximum quadrature squeezing of the light generated by the laser, operating far below threshold, is found to be 50% below the vacuum-state level. We have also established that the mean photon number in the presence of spontaneous emission is less than the absence of spontaneous emission.

Terahertz absorption-saturation and emission from electron-doped germanium quantum wells.

We study radiative relaxation at terahertz frequencies in n-type Ge/SiGe quantum wells, optically pumped with a terahertz free electron laser. Two wells coupled through a tunneling barrier are designed to operate as a three-level laser system with non-equilibrium population generated by optical pumping around the 1→3 intersubband transition at 10 THz. The non-equilibrium subband population dynamics are studied by absorption-saturation measurements and compared to a numerical model. In the emission spectroscopy experiment, we observed a photoluminescence peak at 4 THz, which can be attributed to the 3→2 intersubband transition with possible contribution from the 2→1 intersubband transition. These results represent a step towards silicon-based integrated terahertz emitters.

Three-level all-fiber laser at 915 nm based on polarization-maintaining Nd3+-doped silica fiber

Nd3+-doped fiber lasers at around 900 nm based on the 4F3/2 → 4I9/2 transition have obtained much research attention since they can be used as the laser sources for generating pure blue fiber lasers through the frequency doubling. Here, an all-fiber laser at 915 nm was realized by polarization-maintaining Nd3+-doped silica fiber. A net gain per unit length of up to 1.0 dB/cm at 915 nm was obtained from a 4.5 cm fiber, which to our best knowledge is the highest gain coefficient reported in this kind of silica fiber. The optical-to-optical conversion efficiency varies with the active fiber length and the reflectivity of the output fiber Bragg grating (FBG), presenting an optimal value of 5.3% at 5.1 cm fiber length and 70% reflectivity of the low reflection FBG. Additionally, the linear distributed Bragg reflector short cavity was constructed to explore its potential in realizing single-frequency 915 nm fiber laser. The measurement result of longitudinal-mode properties shows it is still multi-longitudinal mode laser operation with 40 mm laser cavity. These results indicate that the Nd3+-doped silica fiber could be used to realize all-fiber laser at 915 nm, which presents potential to be the seed source of high-power fiber laser.

Three-level laser heat engine at optimal performance with ecological function.

Although classical and quantum heat engines work on entirely different fundamental principles, there is an underlying similarity. For instance, the form of efficiency at optimal performance may be similar for both types of engines. In this work, we study a three-level laser quantum heat engine operating at maximum ecological function (EF) which represents a compromise between the power output and the loss of power due to entropy production. We present numerical as well as analytic results for the global and local optimization of our laser engine in different operational regimes. Particularly, we observe that in low-temperature regimes, the three-level laser heat engine can be mapped to Feynman's ratchet and pawl model, a steady-state classical heat engine. Then we derive analytic expressions for efficiency under the assumptions of strong matter-field coupling and high bath temperatures. Upper and lower bounds on the efficiency exist in case of extreme asymmetric dissipation when the ratio of system-bath coupling constants at the hot and the cold contacts respectively approaches zero or infinity. These bounds have been established previously for various classical models of Carnot-like engines. Further, for weak (or intermediate) matter-field coupling in the high-temperature limit, we derive some new bounds on the efficiency of the engine. We conclude that while the engine produces at least 75% of the power output as compared with the maximum power conditions, the fractional loss of power is appreciably low in case of the engine operating at maximum EF, thus making this objective function relevant from an environmental point of view.

Absolute frequency measurements for emission transitions of molecular iodine in the range of 1053 – 1068 nm

Results of high-precision frequency measurements are presented for certain components of the 127I2 hyperfine structure, which correspond to emission transitions of the B – X band in the range of 1053 – 1068 nm. The frequencies are measured by using a femtosecond optical frequency synthesiser based on a Ti:sapphire laser. The hyperfine structure is resolved by the method of three-level laser spectroscopy. The frequency-doubled cw Nd : YAG laser is used as an excitation radiation source, and the probe radiation in the range of 1050 – 1070 nm is generated by an external-cavity diode laser. The frequencies of both lasers are simultaneously locked to those of two adjacent hyperfine structure components of iodine lines, which have a common upper level. Correspondingly, the frequency of the Nd : YAG laser is locked to the frequency of the absorption transition component, and the diode laser frequency – to the frequency of the emission transition component. The radiation frequency of the diode laser ‘locked’ in this way is measured. Frequencies of 18 hyperfine structure components for six emission lines corresponding to the bands (32 – 54) and (32 – 53) are measured. The relative uncertainty of the measurement is 8 × 10–10.

915 nm all-fiber laser based on novel Nd-doped high alumina and yttria glass @ silica glass hybrid fiber for the pure blue fiber laser.

The fiber laser in the range of 900-1000nm is essential to generate the blue fiber laser through frequency doubling for the laser display, laser underwater communications, and laser lighting. Yet, the well-developed three-level Yb-doped fiber laser can only realize the blue-green fiber laser at around 490nm, which is far from the pure blue area (450nm). To further achieve the pure blue fiber laser, the Nd-doped fiber has emerged as a proper choice to realize a shorter wavelength laser (<920 nm) through the F3/24→I9/24 transition of Nd3+. Here, based on the facile "melt-in-tube" (MIT) method, a novel Nd-doped high alumina and yttria glass @ silica glass hybrid fiber was successfully prepared using the Nd:YAG crystal as the precursor core. The crystal core converts to the amorphous glass state after the drawing process, as evidenced by Raman spectra. The gain coefficient at 915nm of the hybrid fiber reaches 0.4dB/cm. Further, the laser oscillation at 915nm with over 50dB signal-to-noise ratio was realized by a short 3.5cm gain fiber. Our results indicate that MIT is a feasible strategy to produce novel fiber for generating fiber laser at special wavelengths.

Highly efficient cladding-pumped single-mode three-level Yb all-solid photonic bandgap fiber lasers.

Efficient cladding-pumped three-level Yb fiber lasers are difficult to achieve due to the competing four-level system and necessary high inversions. We demonstrate an efficiency of ∼62.7% versus a coupled pump, a record for cladding-pumped fiber lasers with a single-pass pump. 84W at ∼978 nm with ∼1.12M2 was achieved, a record power for flexible fibers. Amplified spontaneous emission was suppressed by >40 dB. The efficiency is quantum-limited ∼94% versus an absorbed pump. This is made possible by the use of a photo-darkening-free Yb phosphosilicate core and recent progress in single-mode large-core all-solid photonic bandgap fiber designs, which provide the necessary large core-to-cladding ratio and suppression of the four-level system.

The Quantum analysis of Nondegenerate Three-Level Laser with Spontaneous Emission and Noiseless Vacuum Reservoir

The analysis of quantum properties of the cavity light produced by a coherently driven nondegenerate three-level laser possessing an open cavity and coupled to a two-mode vacuum reservoir is presented. The normal ordering of noise operators associated with the vacuum reservoir is considered. Applying the solutions of the equations of evolution for the expectation values of the atomic operators and the quantum Langevin equations for the cavity mode operators, the squeezing properties, entanglement amplification, and the normalized second-order correlation function of the cavity radiation are described. The three-level laser generates squeezed light under certain conditions, with maximum intracavity squeezing being 50% below the vacuum-state level. Moreover, it is found that the presence of spontaneous emission increases the quadrature squeezing and entanglement and decreses the mean photon number of the two-mode cavity radiation.

Electron-beam-excited high-pressure He – Ar mixture as a potential active medium for an optically pumped laser

The possibility of developing a laser with optical pumping of metastable ArI levels produced by a relativistic electron beam in high-pressure He – Ar gas mixtures is investigated. It is shown that a high population of the 1s5 level of the argon atom, a wide (∼10 nm) absorption spectral line, and a great lifetime allow us to obtain, as a result of electron beam impact, optimal lasing conditions within the framework of the classical three-level laser scheme. The rate constants of two- and three-particle collisional relaxation processes of low-lying 4s levels of an excited argon atom in He – Ar mixtures in the pressure range from 4 to 0.75 atm are measured.

Study of Lasing Action in a Pulsed Optically Pumped D2O Gas Terahertz Laser

A modified three-level laser kinetics model for a pulsed high-power optically pumped gas terahertz laser is introduced and used to model the lasing kinetics process of a gas terahertz laser system. We, for the first time to our knowledge, investigated the time evolution dynamics process of the pump intensity, population distribution among the energy levels, pump and THz signal gain coefficient, and the THz laser intensity within the pulsed D2O gas THz laser. High-power THz pulse with peak power of about 7.4 kW and pulse width of 145 ns at wavelength of 385 μm were obtained in the simulation, using an incident pump pulse with peak power of 2.2 MW and pulse width of 110 ns. THz pulse delay of 40 ns and pulse broadening of 35 ns were quantitatively analyzed. In addition, the experimental results for the pulse profile, pulse width, pulse broadening, pulse energy, and peak power are in agreement with the theoretical simulation results.

Enhancement of Squeezing and Entanglement in a Non-Degenerate Three-Level Cascade Laser with Coherently Driven Cavity

We study a nondegenerate three-level cascade laser coupled to a two-mode vacuum reservoir, by employing the stochastic differential equations associated with the normal ordering. The amplification of the properties of squeezing and entanglement of the cavity light is investigated. We have found that there is an entanglement between the states of the light generated in the cavity, due to the strong correlation of the light emitted, when the atom decays from the top level to the bottom level via the intermediate one. We have also obtained that the two cavity modes are strongly entangled, and the degree of entanglement is directly related to the two-mode squeezing.

Theoretical and experimental investigation of polarization coexistence and switching in an optical bistability Tm,Ho:LLF laser.

We first investigate the polarization coexistence and switching between the orthogonal π- and σ-polarization states in a free running optical bistability Tm,Ho:LLF laser. The output performances of the optical bistability Tm,Ho:LLF laser is numerically simulated, based on a new rate equation theory model taking into account the influences of polarization-dependent gain and losses. The simulation results show the polarization coexistence and switching of output laser in the process of decreasing pump power. The physical mechanism of polarization coexistence and switching is clarified by analyzing the polarization-dependent net-gain coefficients. Furthermore, the polarization coexistence and switching are experimentally realized in the optical bistability Tm,Ho:LLF laser, which validates the theoretical analysis. The theoretical model can be applied to analyze the polarization coexistence and switching in other kinds of (quasi-) three-level optical bistable lasers.

Modeling of Self-Pumped Singly Resonant Optical Parametric Oscillator

A model of the steady-state operating, self-pumped singly resonant optical parametric oscillator (SPSRO) has been developed. The characteristics of quasi three-level laser gain medium pumped longitudinally have been taken into account. The characteristics of standing wave cavity, reabsorption losses, focusing Gaussian beams of the pump laser, fundamental laser and signal wave have been considered in the analyses. Furthermore, The power characteristics of threshold and efficiency have been analyzed, employing a Yb3+-doped periodically poled lithium niobate co-doped with MgO (Yb3+:MgO:PPLN) as the medium of laser gain and second-order nonlinear crystal.

One-way Einstein–Podolsky–Rosen steering with the aid of the thermal noise in a correlated emission laser

We present to use the thermal noise as an effective way to manipulate the direction of Einstein–Podolsky–Rosen (EPR) steering. In particular, a system of three-level cascade laser is under our consideration, in which the atoms are prepared in an initial superposition of the upper excited level and ground level and the cavity modes are damped by the thermal bath. It is found that the thermal noise plays a constructive role in realizing the one-way EPR steering and expanding the parameter region of the steady-state asymmetric steering. In the absence of the thermal noise, two-way steering mainly occurs due to the injected atomic coherence that is quite helpful for entanglement enhancement. Surprisingly, when the thermal noise is involved, the one-way steering substitutes for two-way steering and it can be obtainable in most parameter region. Actually, the thermal noise significantly increases the mean number of the emitted photon pairs and enlarges the intensity difference between two cavity modes, which leads to the striking asymmetry in the mean photon numbers and then induces the unidirectional steerability from the mode generated by the upper transition to the mode in the low transition. The present scheme may provide a resource in a long-distance quantum network for quantum secret sharing protocol.

Tuning terahertz transitions in a double-gated quantum ring

We theoretically investigate the optical functionality of a semiconducting quantum ring manipulated by two electrostatic lateral gates used to induce a double quantum well along the ring. The well parameters and corresponding inter-level spacings, which lie in the THz range, are highly sensitive to the gate voltages. Our analysis shows that selection rules for inter-level dipole transitions, caused by linearly polarized excitations, depend on the polarization angle with respect to the gates. In striking difference from the conventional symmetric double well potential, the ring geometry permits polarization-dependent transitions between the ground and second excited states, allowing the use of this structure in a three-level lasing scheme.

Atom and field squeezed output of three-level atom laser surrounded by a Kerr medium in the electromagnetically induced transparency regime

In this paper, we investigate the squeezing properties of the output of an atom laser which consists of an ensemble of three-level atoms in Bose–Einstein condensate state interacting with two quantized and classical laser fields in the presence of a Kerr medium. We represent the Hamiltonian of the system under an electromagnetically induced transparency regime and using the adiabatical elimination process, in terms of angular momentum operators, and then deduce the corresponding analytical state vector with the help of the Dicke model. We give our attention to the evaluation of atomic and field squeezings via numerical calculations. The results show that nonlinear sources in the system, i.e., “interatom collisions” and “Kerr medium,” lead to squeezing of atoms and photons. In this respect, the squeezing values can be controlled by adjusting the strength of interatom collisions, the Kerr medium, as well as other involved parameters in the considered model. Also, the collapse-revival phenomenon as a pure quantum feature can be observed in the behavior of atomic squeezing, while only irregular oscillations appeared in the field squeezing.

Two-well terahertz quantum cascade lasers with suppressed carrier leakage

The mechanisms that limit the temperature performance of diagonal GaAs/Al0.15GaAs0.85-based terahertz quantum cascade lasers (THz-QCLs) have been identified as thermally activated leakage of charge carriers through excited states into the continuum. THz-QCLs with energetically higher-laying excited states supported by sufficiently high barriers aim to eliminate these leakage mechanisms and lead to improved temperature performance. Although suppression of thermally activated carrier leakage was realized in a three-well THz-QCL based on a resonant-phonon scheme, no improvement in the temperature performance was reported thus far. Here, we report a major improvement in the temperature performance of a two-quantum-well direct-phonon THz-QCL structure. We show that the improved laser performance is due to the suppression of the thermally activated carrier leakage into the continuum with the increase in the injection barrier height. Moreover, we demonstrate that high-barrier two-well structures can support a clean three-level laser system at elevated temperatures, which opens the opportunity to achieve temperature performance beyond the state-of-the-art.

Mid-infrared emission in Tb^3+-doped selenide glass fiber

The mid-infrared (MIR) emission behavior of Tb3+-doped Ge–As–Ga–Se bulk glasses (500, 1000, and 1500 ppmw Tb3+) and unstructured fiber (500 ppmw Tb3+) is investigated when pumping at 2.013 μm. A broad emission band is observed at 4.3–6.0 μm corresponding to F57→F67, with an observed emission lifetime of 12.9 ms at 4.7 μm. The F47 level is depopulated nonradiatively and so it is proposed that Tb3+-doped Ge–As–Ga–Se fiber may operate as a quasi-three-level MIR fiber laser. Underlying glass-impurity vibrational absorption bands are numerically removed to give the true Tb3+ absorption cross section, as required for Judd–Ofelt (J–O) analysis. Radiative transition rates calculated from J–O theory are compared with measured lifetimes. A numerical model of the three-level Tb3+-doped fiber laser is developed for Tb3+ doping of 8.25×1024 ions m−3 (i.e., 500 ppmw) and dependence of laser performance on fiber length, output coupler reflectivity, pump wavelength, signal wavelength, and fiber background loss is calculated. Results indicate the feasibility of an efficient three-level MIR fiber laser operating within 4.5–5.3 μm, pumped at either 2.013 or 2.95 μm.

Stimulated emission and lasing in laser-induced plasma plume

The lasing effect is demonstrated in laser plasmas induced on various metal targets and pumped by a laser tuned in resonance with a strong optical transition of a metal. The intense, polarized and low-divergent radiation is emitted from a longitudinally pumped plasma plume in forward and backward directions with respect to the pump beam. Lasing occurs only within duration of the pumping pulse. The effect is found for elements of 13th and 14th groups and for Ca, Ti, Zr, Fe and Ni. The Einstein coefficients for spontaneous emission of all lasing transitions are higher than 107s−1. For some elements like Al and In, a three-level lasing scheme is realized. For others, like Tl, both three- and four-level lasing schemes are realized. It is found that the longitudinal pump geometry is more efficient than the transversal one.