Laser Frequency Detuning Research Articles

Exceptional points with waveguide-coupled nanolasers

Exceptional points (EPs) attract lots of attention due to the richness of the phenomenology associated to their presence in the complex eigenspectrum of coupled non-Hermitian systems. Here we provide both a coupled mode theory analysis and an experimental investigation of two nanolasers interacting through a channel-mediated coupling. We demonstrate the transition from Parity-Time (PT) symmetric to PT-broken regime using a thermo-optic control over the laser frequency detuning

Optical feedback noise-immune cavity-enhanced optical heterodyne molecular spectrometry for sub-Doppler-broadened detection of C2H2.

A novel, to the best of our knowledge, noise-immune cavity-enhanced optical heterodyne molecular spectrometry (NICE-OHMS) has been developed, utilizing optical feedback for laser-to-cavity locking with a common distributed-feedback diode laser. The system incorporates active control of the feedback phase and feedforward control of the laser current, allowing for consecutive laser frequency detuning by scanning a piezoelectric transducer (PZT) attached to the cavity. To enhance the fidelity of the spectroscopic signal, wavelength-modulated (wm) NICE-OHMS is implemented. Benefiting from the optical feedback, a modulation frequency of 15 kHz is achieved, surpassing the frequencies typically used in traditional NICE-OHMS setups. Then, the sub-Doppler-broadened wm-NICE-OHMS signal of acetylene at 1.53 µm is observed. A seven-fold improvement in signal to noise ratio has been demonstrated compared to NICE-OHMS alone and a limit of detection of 6.1 × 10-10cm-1 is achieved.

Formation and manipulation of optical soliton pulse in a self- and cross-phase modulated four-level inverted Y-type system

We have proposed a theoretical model for controllable optical soliton pulse formation in a magnetic-field-assisted four-level inverted Y-type atomic system. The probability amplitudes of the pertinent levels are used to analyze the contrast between self- and cross-phase modulated probe absorption signals. The absorption profiles obtained from the probability amplitudes and the zeroth-order of the pulse propagation constant in the Taylor series are appropriately congruent. The nonlinear Schrödinger equation derived from the Maxwell–Bloch equation determines the respective bright and dark soliton conditions with positive and negative values of the pulse shape parameter. It is demonstrated that the coupling laser field strengths, laser frequency detunings, and the external magnetic field’s direction are the controlling parameters to produce both bright and dark optical soliton pulses. Alongside, the shape of the optical soliton pulses in self- and cross-phase modulation is influenced by the polarization angle of the probe and coupling fields. It is also found that the variation of coupling field strengths may be used to regulate the group velocity of the soliton probe pulse from superluminal to subluminal modes or vice-versa.

Chimera states in a large laterally coupled laser array with four different waveguide structures.

Chimera states are rich and fascinating phenomena existing in many networks, where the identical oscillators self-organize into spatially separated coexisting domains of coherent and incoherent oscillations. Here, we report these states in the large laterally coupled laser array with four different waveguiding structures, with which a variety of chimera patterns can be revealed. We present the bifurcation diagrams giving birth to them and find that the chimeras exist in the boundary of the steady state and multi-period oscillation solutions, which applies to all the prevalent waveguiding structures considered. We also find that the waveguiding structures play an important role in the chimera states, e.g., the array composed of the index antiguiding with gain-guiding has a wider chimera region compared to other waveguides considered. Additionally, the effects of the crucial parameters including the laser separation ratio, pump rate, frequency detuning, and linewidth enhancement factor on the observed phenomena are discussed. Our analysis shows that the frequency detuning between lasers and the linewidth enhancement factor affects the lifetime and pattern of chimeras. The results could guide the design of laser arrays or introduce more insight into a new understanding of the dynamical behaviors of networks.

Exploiting the two-dimensional magneto-optical trapping of Hg199 for a mercury optical lattice clock

Two-dimensional magneto-optical trapping (2D-MOT) is an efficient tool for generating a high flux of precooled atoms. A 2D-MOT for mercury (Hg) is so far missing despite the potential of this atomic species in several areas. Here, we present the characterization of a 2D-MOT for Hg enabled by addressing the ${}^{1}{S}_{0}$- ${}^{3}{P}_{1}$ laser cooling transition at 254 nm. The laser source based on an ytterbium-doped fiber amplifier has low-frequency noise and high reliability. Parameters affecting the efficiency of the 2D-MOT are studied, i.e., optical trapping power, push beam power, cooling laser frequency detuning, and magnetic-field gradient. When used with a Hg optical lattice clock, the 2D-MOT increases by a factor of 4.5, the rate of preparation of the atomic samples, yielding an improved clock short term stability of $6.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ at 1 s.

Sensitivity enhancement of nonlinear refractive index measurement by Gaussian-Bessel beam assisted z-scan method.

Characterizing the nonlinear optical properties of numerous materials plays a prerequisite role in nonlinear imaging and quantum sensing. Here, we present the evaluation of the nonlinear optical properties of Rb vapor by the Gaussian-Bessel beam assisted z-scan method. Owed to the concentrated energy in the central waist spot and the constant intensity of the beam distribution, the Gaussian-Bessel beam enables enhanced sensitivity for nonlinear refractive index measurement. The nonlinear self-focusing and self-defocusing effects of the Rb vapor are illustrated in the case of blue and red frequency detunings from 5S1/2 - 5P3/2 transition, respectively. The complete images of the evolution of nonlinear optical properties with laser power and frequency detuning are acquired. Furthermore, the nonlinear refractive index n2 with a large scale of 10-6 cm2/W is determined from the measured transmittance peak-to-valley difference of z-scan curves, which is enhanced by a factor of ∼ 1.73 compared to the result of a equivalent Gaussian beam. Our research provides an effective method for measuring nonlinear refractive index, which will considerably enrich the application range of nonlinear material.

Effect of Coulomb interaction on the transient optical response of electrons in field-coupled quantum dots

In this work, we develop a physically transparent Coulomb-interaction model from simplification of a general many-body theory and apply this model to study interacting electron dynamics for transient occupation and quantum coherence in both single and double quantum dots under laser irradiation. Our theory considers self-consistently the Coulomb-renormalized Rabi coupling to light by using an induced optical-depolarization field, corresponding to dynamical exchange interaction between two electrons within the same quantum dot. Meanwhile, we employ evanescent-field coupling for dynamical Coulomb interaction between two electrons in different quantum dots based on a surface-plasmon model. In particular, we explore the quantum interference between a pair of laser-induced quantum coherence in three-level quantum-dot systems, which gives rise to indirect transition of electrons for sum- and difference-frequency transient optical responses. By varying laser frequency detuning, the control of laser-dressed electronic states becomes possible and can be utilized for switching among off-state, partial, and complete on-states. This study will be useful for controlling the phase entanglement of two laser-dressed states of quantum dots, as well as for enhancing the electro-optical performance through sum- and difference-frequency transitions in many optoelectronic devices.

Measurement of the Kerr nonlinear refractive index of the Rb vapor based on an optical frequency comb using the z-scan method.

We report the measurement of the Kerr nonlinear refractive index of the rubidium vapor via the high sensitivity z-scan method by using an optical frequency comb. The novel self-focusing and self-defocusing effects of the vapor are presented with red and blue detunings of the laser frequency. The optical nonlinear characteristics of the rubidium vapor are clearly interpreted under different experimental parameters. Furthermore, the Kerr nonlinear refractive index n2 is obtained from the measured dispersion curve, and it basically occurs on the order of 10-6 cm2/W. The evolutions of the Kerr nonlinear coefficient n2 with the laser power and frequency detuning, respectively, are studied. To the best of our knowledge, the use of pulsed lasers to measure the Kerr nonlinear refractive index n2 of atomic vapor has not been reported yet. The direct measurement of the Kerr nonlinear coefficient will greatly help us understand and optimize nonlinear optical processes and find its more potential applications in quantum optics.

Experimental creation of single Rydberg excitations via adiabatic passage

In an atomic ensemble, quantum information is typically carried as single collective excitations. It is very advantageous if the creation of single excitations is efficient and robust. Rydberg blockade enables deterministic creation of single excitations via collective Rabi oscillation by precisely controlling the pulse area, being sensitive to many experimental parameters. In this paper, we implement the adiabatic rapid passage technique to the Rydberg excitation process in a mesoscopic atomic ensemble. We make use of a two-photon excitation scheme with an intermediate state off-resonant and sweep the laser frequency of one excitation laser. We find the chirped scheme preserves internal phases of the collective Rydberg excitation and be more robust against variance of laser intensity and frequency detuning.

A Compact Laser Pumped 4He Magnetometer with Laser-Frequency Stabilization by Inhomogeneous Light Shifts

We propose a compact 4He magnetometer realizing magnetic field measurement and laser-frequency stabilization simultaneously in a single 4He atomic cell. The frequency stabilization scheme is based on the asymmetric line shape of magnetic resonance which is induced by spatially inhomogeneous light shifts. We investigate the asymmetric line shape of the magnetic resonance signal theoretically and experimentally in laser pumped 4He magnetometer with the magneto-optical double-resonance configuration. Notice that, due to the asymmetric line shape, the in-phase component of the magnetic resonance signal is shown to have a linear dependence with respect to the laser frequency detuning and is used to actively lock the laser frequency to the resonant point. The method reduces the complexity of the system and improves the stability of the magnetometer, making the laser-pumped 4He magnetometer more compact and portable.

Phase-Modulated Entangling Gates Robust to Static and Time-Varying Errors

Entangling operations are among the most important primitive gates employed in quantum computing and it is crucial to ensure high-fidelity implementations as systems are scaled up. We experimentally realize and characterize a simple scheme to minimize errors in entangling operations related to the residual excitation of mediating bosonic oscillator modes that both improves gate robustness and provides scaling benefits in larger systems. The technique employs discrete phase shifts in the control field driving the gate operation, determined either analytically or numerically, to ensure all modes are de-excited at arbitrary user-defined times. We demonstrate an average gate fidelity of 99.4(2)% across a wide range of parameters in a system of $^{171}\text{Yb}^{+}$ trapped ion qubits, and observe a reduction of gate error in the presence of common experimental error sources. Our approach provides a unified framework to achieve robustness against both static and time-varying laser amplitude and frequency detuning errors. We verify these capabilities through system-identification experiments revealing improvements in error-susceptibility achieved in phase-modulated gates.

Controlling optical multistability and bistability in four-level cascade quantum wells

Optical multistablity (OM) and bistability (OB) are investigated theoretically in the four-level cascade quantum wells (QWs) with two similar transitions for the probe laser. It is interesting that the system can be transited from OM to OB by enhancing the coupling laser field or reducing its frequency detuning. In the same time, both of them can also be used to control the OM behavior along with the other corresponding parameters such as the electronic cooperation parameter, the probe laser frequency detuning and the decay rate. Such a system is more practical than those in the atomic systems for the flexibility of QWs, and may be used in the all optical switches or other solid-state quantum information devices.

Nonlinear dynamic instability of Landau-quantized graphene inside an optical ring cavity

Controlling dynamic behaviors, such as instability and chaos, in various systems has been a central matter of nonlinear physics in recent years. Here we employ an effective density-matrix method for the study of laser beam propagation through an optical ring cavity containing Landau-quantized graphene nanostructures. By taking into account the linear and nonlinear phase shifts, we detailedly investigate and characterize the nonlinear dynamic behaviors of the transmission field and the results show that the system exhibits dynamic instability. The start and termination, as well as the periodicity of this dynamic oscillations inside the optical cavity can be manipulated by the experimentally achievable parameters, such as the laser intensity and frequency detuning. Such dynamic responses are attributed to the competition between optical saturation of the incident field and population oscillations induced by the control field in graphene system.

Suppressing Two-Plasmon Decay with Laser Frequency Detuning.

Three-dimensional laser-plasma interaction simulations show that laser frequency detuning by an amount achievable with current laser technology can be used to suppress the two-plasmon decay (TPD) instability and the corresponding hot-electron generation. For the plasma conditions and laser configuration in a direct-drive inertial confinement fusion implosion on the OMEGA laser, the simulations show that ∼0.7% laser frequency detuning is sufficient to eliminate TPD-driven hot-electron generation in current experiments. This allows for higher ablation pressures in future implosion designs by using higher laser intensities.

Two-photon coherent spectroscopy of ultracold Li atoms

Our work is devoted to theoretical study of the two-photon coherent spectroscopy of 7Li atoms continuously cooled in a magneto-optical trap (MOT) on the 2S–2P transition. The ultracold atoms are transferred to highly excited Rydberg states in a two-step coherent excitation process by red and UV lasers. The red laser is detuned by -600 MHz from 2S–2P transition frequency and UV laser frequency detuning is scanned in the vicinity of +600 MHz from 2P-nS(D) transition where n∼40-100 is principal quantum number. The fluorescence signal on the 2P–2S cooling transition makes it possible to obtain a two-photon absorption spectrum. Atom-field interaction is considered in the simple three-level approximation involving a density matrix formalism. It is shown that the effect of the MOT beams on the shape of the two-photon absorption line can be taken into account by an appropriate change in the 2S–nS(D) coherence decay rate.

Optical cooling and trapping of highly magnetic atoms: the benefits of a spontaneous spin polarization

From the study of long-range-interacting systems to the simulation of gauge fields, open-shell lanthanide atoms with their large magnetic moment and narrow optical transitions open novel directions in the field of ultracold quantum gases. As for other atomic species, the magneto-optical trap (MOT) is the working horse of experiments but its operation is challenging, due to the large electronic spin of the atoms. Here we present an experimental study of narrow-line dysprosium MOTs. We show that the combination of radiation pressure and gravitational forces leads to a spontaneous polarization of the electronic spin. The spin composition is measured using a Stern–Gerlach separation of spin levels, revealing that the gas becomes almost fully spin-polarized for large laser frequency detunings. In this regime, we reach the optimal operation of the MOT, with samples of typically atoms at a temperature of 15 μK. The spin polarization reduces the complexity of the radiative cooling description, which allows for a simple model accounting for our measurements. We also measure the rate of density-dependent atom losses, finding good agreement with a model based on light-induced Van der Waals forces. A minimal two-body loss rate cm3 s–1 is reached in the spin-polarized regime. Our results constitute a benchmark for the experimental study of ultracold gases of magnetic lanthanide atoms.

Doppler-free three-photon coherence in Doppler-broadened diamond-type atomic system.

We investigated the relationship between three-photon electromagnetically induced absorption (TPEIA) and four-wave mixing (FWM) in the 5S1/2-5P3/2-5D5/2 transition of 87Rb atoms. When the driving field was additionally coupled to the ground and intermediate states of a lower V-type configuration in a typical ladder-type electromagnetically induced transparency (EIT) system, Doppler-free TPEIA and FWM spectra were simultaneously observed and then analyzed from the perspective of multi-photon atomic coherence. Comparing the TPEIA and FWM spectra according to the laser frequency detuning and laser intensity, we found that the enhanced TPEIA signal is strongly correlated with the generated FWM light. Analytical and numerical calculations for the analysis of the relationship are presented.

Rubidium chip-scale atomic clock with improved long-term stability through light intensity optimization and compensation for laser frequency detuning

We demonstrate the implementation of a Rb87 chip-scale atomic clock (CSAC) that has improved long-term stability. A simple method of reducing the frequency drift in the CSAC is proposed. As well as the well-known effect of light intensity on the clock frequency, our analysis shows that the frequency drift that is due to laser frequency detuning (LFD) variation originates from asymmetry in the coherent laser fields, and thus, we propose to actively compensate the clock frequency by using variations in the light intensity and LFD. We performed experiments to obtain precise clock frequency sensitivities to the light intensity and LFD, and the frequency drift was reduced from 7.1×10−11/day to 6.9×10−13/day with the frequency compensation method. Additionally, the CSAC with an optimized configuration of light intensity and microwave power showed evident long-term frequency stability improvement, from 8.9×10−11 to 8.7×10−12 at 105 s. Therefore, our method is useful in reducing the frequency drift of CSACs and could be potentially used in applications that require moderate long-term stability of sub-1×10−11.

Atomic coherence effects in four-wave mixing process of a ladder-type atomic system.

We investigate the effects of atomic coherence on four-wave mixing (FWM), with respect to the transition routes between the hyperfine states in the 5S1/2-5P3/2-5D5/2 transition of 87Rb atoms. By comparing the FWM spectra with the electromagnetically induced transparency (EIT) spectra of the hyperfine states, we confirm that the FWM process is significantly influenced by both ladder-type and V-type two-photon coherences. From the observed FWM signal of each hyperfine structure, we clarify the role of two-photon coherence in the FWM process under EIT, double-resonance optical pumping (DROP), and two-photon absorption (TPA) conditions in a ladder-type atomic system, which is dependent on the open degree of the hyperfine states, the laser intensity, and the laser frequency detuning.

Optical switching in dual injection-locked Fabry-Pérot laser diodes

Theoretical study of switching in a Fabry-Perot semiconductor laser under dual injection-locking is performed and presented. The investigation is conducted in the range of multistability, in which up to three stable states of the slave laser can exist simultaneously. We numerically investigate slave laser switching time in the process of simultaneous variation of two injection parameters: the master laser injection power (amplitude controlled switching) and frequency detuning (phase controlled switching). By using this switching mechanism, we obtain significant improvement of the slave laser switching time compared to the mechanism comprising just injection power variation.