Search

In this paper, a nonlinear optical cascaded difference frequency generation model based on double rapid adiabatic passage technique is established, and a theoretical scheme for generating THz waves based on the above model is proposed. In this model, when the incident signal laser interacts with a pump laser, the signal laser can be completely converted into the output laser by special processing of the coupling wave equation and making reasonable assumptions. Numerical simulation results show that THz waves with a centre frequency of 260 GHz can be obtained. The maximum quantum conversion efficiency of the signal laser to THz waves is about 43.4%. Under the premise of keeping the wavelength of the pump laser unchanged, the tunable THz waves of 0.26–2.94 THz can be obtained when tuning the wavelength of the signal laser to change in the range of 1.054–1.064 μ m. Compared with the scheme using stimulated Raman adiabatic passage technique, the scheme can still generate terahertz waves during the application of a pump laser to two simultaneous difference frequency generation processes, and the intensity of the pump laser can be reduced from Gigawatt level to Megawatt level. This scheme is robust to the temperature variation and provides a new method for generating terahertz wave band for high-speed wireless transmission. [ABSTRACT FROM AUTHOR]

We present results on isotopically selective lutetium photoionization using dye lasers pumped by copper vapor lasers as applied to the problem of obtaining the 177Lu radionuclide for medical applications. [ABSTRACT FROM AUTHOR]

Carbon ion irradiation and precise diamond blade dicing are applied to fabricate Nd:GdCOB ridge waveguides. The propagation properties of the fabricated Nd:GdCOB waveguides are investigated through experiments and theoretical analysis. Micro-Raman analysis reveals that the Nd:GdCOB crystal lattice expands during the irradiation process. Micro-second harmonic spectroscopic analysis suggests that the original nonlinear properties of the Nd:GdCOB crystal are greatly enhanced within the waveguide volume. Under pulsed 1064 nm laser pumping, second harmonic generation (SHG) at 532 nm has been achieved in the fabricated waveguides. The maximum SHG conversion efficiencies are determined to be ∼ 8.32 %â‹...Wâˆ'1 and ∼ 22.36 %â‹...Wâˆ'1 for planar and ridge waveguides, respectively. [ABSTRACT FROM AUTHOR]

A high-efficiency and high-power vertical-cavity surface-emitting laser (VCSEL) side-pumped rod Nd:YAG laser with temperature adaptability are demonstrated. The VCSEL side-pumped laser module is designed and optimized. Five VCSEL arrays are symmetrically located around the laser rod and a large size diffused reflection chamber is designed to ensure a uniform pump distribution. Furthermore, the absorbed pump power distribution of the rod is simulated to verify the uniformity of the pump absorption. Finally, a proof-of-principle experiment is performed in short linear cavity laser with single laser module. A continuous-wave output power of 658 W at 1064 nm is obtained, the corresponding optical-to-optical efficiency is 52.6%, and the power variations are ±0.7% over 400 s and ±3.1% over the temperature range from 16 °C to 26 °C. To the best of our knowledge, this is the highest output power and the highest optical-to-optical efficiency ever reported for VCSEL pumped solid-state lasers. By inserting a telescopic module into the cavity and optimizing the TEM00 mode volume, the average beam quality is measured to be M 2 = 1.34 under an output power of 102 W. The experimental results reveal that such a high power rod laser module with temperature stability is appropriate for field applications. [ABSTRACT FROM AUTHOR]

It has been predicted that high-order harmonic generation (HHG) in nanowires has the potential to scale up photon energy and harmonic yield. However, studies on HHG in nanowires are still theoretical and no relevant experimental results have been reported as yet. Our experimental observation of the high-order harmonic in cadmium sulfide nanowires (CdS NWs) excited by a mid-infrared laser is, to our knowledge, the first of such study, and it verifies some of the theoretical results. Our experimental results show that the observed harmonics are strongest when a pump laser is parallel to the nanowires. Therefore, the theoretical prediction that harmonics are strongest under the nanowires parallel to the laser field is confirmed experimentally, and this can be used to determine the orientation of the nanowire. In addition, harmonics are sensitive to the variation of pump light ellipticities. This orientation dependence opens new opportunities to access the ultrafast and strong-field physics of nanowires. [ABSTRACT FROM AUTHOR]

We investigate the ultrafast spin dynamics of an antiferromagnet in a ferromagnet/antiferromagnet heterostructure Fe/GdFeO3 via an all-optical method. After laser irradiation, the terahertz spin precession is hard to be excited in a bare GdFeO3 without spin reorientation phase but efficiently in Fe/GdFeO3. Both quasi-ferromagnetic and impurity modes, as well as a phonon mode, are observed. We attribute it to the optical modification of interfacial exchange coupling between Fe and GdFeO3. Moreover, the excitation efficiency of dynamics can be modified significantly via the pump laser influence. Our results elucidate that the interfacial exchange coupling is a feasible stimulation to efficiently excite terahertz spin dynamics in antiferromagnets. It will expand the exploration of terahertz spin dynamics for antiferromagnet-based opto-spintronic devices. [ABSTRACT FROM AUTHOR]

The dissociation and ionization dynamics of CF3I and CH3I molecules were investigated using a pump-and-probe technique that employs a soft x-ray free-electron laser (SACLA) in Japan. First, time-resolved inner-shell photoelectron spectroscopy was employed to observe the ultrafast reaction of CF3I by monitoring iodine 4d electrons. The change in the I 4d state observed in the photoelectron spectra is found to occur with a rise time τ of approximately 40 fs after a pump laser pulse, which is faster than that observed when an ultrafast gas-phase electron diffraction technique is employed. This implies that the inner-shell photoelectron spectroscopy is more sensitive to the potential surface near the Franck–Condon region. Second, a strong laser intensity at 266 nm, corresponding to a power density of 1.9 × 1014 W cm−2, can easily ionize CH3I molecules via multiphoton ionization processes, and the time dependence of the valence photoelectron spectra clearly shows that at the picosecond timescale, this pump laser pulse causes spectral peaks to shift owing to space-charge effects in response to the large amount of ions generated. Thus, the SACLA can be a useful tool to investigate not only the dynamical process of molecular dissociation but also the ionization process through the shift in the peaks of photoelectron spectra. [ABSTRACT FROM AUTHOR]

We report on the direct generation of optical vortex lattice (OVL) modes from a diode-pumped Pr3+:LiYF4 (Pr:YLF) laser achieved by employing off-axis (transverse) and defocused (longitudinal) pumping geometries in the laser medium. OVL modes with more than 40 phase singularities are generated. The experimentally observed OVL modes are well supported by a theoretical analysis based on the superposition of Hermite-Gaussian modes. We also discuss the intracavity frequency doubling of the OVL modes. The proposed OVL mode laser system can be applied to fundamental optical science and advanced material engineering. [ABSTRACT FROM AUTHOR]

A new approach for analytically solving quantum nonlinear Langevin equations is proposed and applied to calculations of spectra of superradiant lasers where collective effects play an important role. We calculate lasing spectra for arbitrary pump rates and recover well-known results such as the pump dependence of the laser linewidth across the threshold region. We predict new sideband peaks in the spectrum of superradiant lasers with large relaxation oscillations as well as new nonlinear structures in the lasing spectra for weak pump rates. Our approach sheds new light on the importance of population fluctuations in the narrowing of the laser linewidth, in the structure of the lasing spectrum, and in the transition to coherent operation. [ABSTRACT FROM AUTHOR]

High-precision temperature measurement with adjustable operating range is investigated and experimentally demonstrated based on weak measurement in the frequency domain. The operating range of measurement is precisely modulated by introducing a dynamic extra time delay to the post-selection pumped by a femtosecond laser. By choosing appropriate nonlinear materials and the attenuation, the resolution of the optimized extra time delay can be improved by two orders of magnitude over that of a traditional phase delay compensator. Considering the influence of noise in the experiment, the highest precision of 8.03 × 10−7 °C can be achieved by using a currently available spectrometer. Moreover, the average sensitivity can reach to 38 nm/°C. Taking advantage of the high precision and adjustable operating range, the proposed method has great potential applications in high-precision temperature measurements. [ABSTRACT FROM AUTHOR]

Tunable diode laser induced fluorescence (TDLIF) measurements are discussed and quantitatively evaluated for nitrogen admixtures in argon plasma under the influence of a strong magnetic field. TDLIF measurements were used to evaluate light-transport properties in a strongly magnetized optically thick argon/nitrogen plasma under different pressure conditions. Therefore, a coupled system of rate balance equations was constructed to describe laser pumping of individual magnetic sub-levels of 2p8 state through frequency-separated sub-transitions originating from 1s4 magnetic sub-levels. The density distribution (alignment) of 2p8 multiplet was described by balancing laser pumping with losses including radiative decay, transfer of excitation between the neighboring sub-levels in the 2p8 multiplet driven by neutral collisions (argon and nitrogen) and quenching due to electron and neutral collisions. Resulting 2p8 magnetic sub-level densities were then used to model polarization dependent fluorescence, considering self-absorption, which could be directly compared with polarization-resolved TDLIF measurements. This enables to estimate the disalignment rate constant for the 2p8 state due to collisions by molecular nitrogen. A comparison to molecular theory description is given providing satisfactory agreement. The presented measurement method and model can help to describe optical emission of argon and argon–nitrogen admixtures in magnetized conditions and provides a basis for further description of optical emission spectra in magnetized plasmas. [ABSTRACT FROM AUTHOR]

The magnetic excitons in diluted magnetic semiconductor (DMS) have varied formats due to the inhomogeneous phases out of doping concentration and/or structural relaxations or defects. Here the high quality cobalt-doped zinc blende ZnSe nanoribbons (NRs) were synthesized, showing bright and color-variable emissions from blue, yellow to a little mixed white colors. Their power and temperature dependent micro-photoluminescence (PL) spectra have been obtained in which two emission bands, one magnetic exciton band near the band-edge and a Co2+ high-level d–d transition emission band at 550 nm out of their ferromagnetic (FM) coupled aggregates in ZnSe lattice, both bands could also be reflected by a nonlinear optical absorption enhancement. The easy formed stacking fault defects in a chemical vapor deposition (CVD) grown ZnSe zincblende NR took part in the above optical processes out of magnetic polaronic excitons (PXs). The femtosecond (fs) laser pulse pumping on single ZnSe:Co NR produces obvious lasing behavior but with profile of a complicated magnetic exciton interactions with indication of a crossover from collective exciton magnetic polarons (EMP) to bound magnetic polaron (BMP) scattering in Co doped ZnSe NR. These findings indicate the complication of the magnetic coupling natures in varied DMS structures, whose optical properties have been found to be highly nonlinear, due to the involvement of the spin–spin, spin–exciton and spin–phonon interactions, verified by the theoretic calculation in Yang X-T et al (2019 Interstitial Zn-modulated ferromagnetism in Co-doped ZnSe Mater. Res. Express 6 106121). [ABSTRACT FROM AUTHOR]

We report pulsed laser diode (LD) end-pumped acoustic Q-switched Tm:YAG laser, Tm:LuAG laser, and Tm:LuYAG laser and the physical properties and spectra of Tm:YAG, Tm:LuAG, and Tm:LuYAG are analyzed. The Tm:LuYAG laser is pumped by 785-nm and 788-nm pulses separately, and is compared with Tm:YAG laser. Different output energy values and output wavelengths of Tm:LuAYG lasers pumped by LDs with different wavelengths are obtained and compared with each other. When the repetition frequency is 100 Hz, the pulsed Tm:YAG laser has single pulse energy of 15.9 mJ, pulse width of 126.7 ns, and the center wavelength of 2013.36 nm, and the pulsed Tm:LuAG laser possesses single pulse energy of 11.8 mJ, pulse width of 252.4 ns, and the center wavelength of 2023.65 nm, and the pulsed Tm:LuYAG laser output energy values are 12.32 mJ and 12.25 mJ with the slope efficiencies of 12.5% and 11.85%, the center wavelengths of 2017.89 nm and 2027.11 nm, respectively, while the pump sources are 785-nm and 788-nm pulsed LDs, respectively. [ABSTRACT FROM AUTHOR]

Considering the atmospheric extinction and turbulence effects, we investigate the propagation performances of super-continuum laser sources in atmospheric turbulence statistically by using the numerical simulation method, and the differences in propagation properties between the super-continuum (SC) laser and its pump laser are also analyzed. It is found that the propagation characteristics of super-continuum laser are almost similar to those of the pump laser. The degradation of source coherence degree may cause the relative beam spreading and scintillation indexes to decrease at different propagation distances or different turbulence strengths. The root-mean-square value of beam wandering is insensitive to the variation of source correlation length, and less aperture averaging occurs when the laser source becomes less coherent. Additionally, from the point of view of beam wandering, the SC laser has no advantage over the pump laser. Although the pump laser can bring about a bigger aperture average, the SC laser has a lower scintillation which may be due to the multiple wavelength homogenization effects on intensity fluctuations. This would be the most important virtue of the SC laser that can be utilized to improve the performance of laser engineering. [ABSTRACT FROM AUTHOR]

Delayed cavity-free forward lasing at the wavelengths of 391 and 428 nm was observed in recent experiments in air or pure nitrogen pumped with an intense femtosecond laser pulse at wavelength of 800 nm. The mechanism responsible for the lasing is highly controversial. In this article we propose a model explaining the delayed lasing, which contains two parts: (i) ionization of neutral nitrogen molecules and subsequent excitation of nitrogen ions in a strong pump laser pulse, and (ii) coherent emission of excited ions due to the presence of long-lived polarizations maintained by a weak laser post-pulse and coupling simultaneously ground state to states A2Πu and of singly ionized nitrogen molecules. Two regimes of signal amplification are identified: a signal of a few picosecond duration at low gas pressures and a short (sub-picosecond) signal at high gas pressures. The theoretical model compares favorably with results obtained by different experimental groups. [ABSTRACT FROM AUTHOR]

In the unresolved sideband regime, we propose a scheme for cooling mechanical resonator close to its ground state in a three-cavity optomechanical system, where the auxiliary cavities are indirectly connected with the mechanical resonator through standard optomechanical subsystem. The standard optomechanical subsystem is driven by a strong pump laser field. With the help of the auxiliary cavities, the heating process is suppressed and the cooling process of the mechanical resonator is enhanced. More importantly, the average phonon number is much less than 1 in a larger range. This means that the mechanical resonator can be cooled down to its ground state. All these interesting features will significantly promote the physical realization of quantum effects in multi-cavity optomechanical systems. [ABSTRACT FROM AUTHOR]

We investigate properties of the ponderomotive squeezing in an optomechanical system with two coupled resonators, where the tunable two-mode squeezing spectrum can be observed from the output field. It is realized that the squeezing orientation can be controlled by the detuning between the left cavity and pump laser. Especially, both cavity decay and environment temperature play a positive role in generating better pondermotive squeezing light. Strong squeezing spectra with a wide squeezing frequency range can be obtained by appropriate choice of parameters present in our optomechanical system. [ABSTRACT FROM AUTHOR]

The prior theoretical model shows that GaSb is one of the few non-alloy semiconductors showing phonons ballistic effect in the thermal conductivity. However, no previous literature had been reported on the experimental measurements on the quasi-ballistic thermal transport of the GaSb thin film. In this paper, we employed the time-domain thermoreflectance (TDTR) to study the thermal transport of nanoparticles embedded GaSb thin film. Our measurements results provide first experimental evidence to verify the quasi-ballistic effect in the thermal transport of the GaSb thin film. The apparent cross-plane thermal conductivity of pure GaSb sample drops ∼15% when the pump laser modulation frequency is increased from 0.8 MHz to 10 MHz at room temperature. To further understand the thermal transport mechanism, Tempered Lévy analysis is employed to study the quasi-ballistic effect of the GaSb thin film. The model shows that GaSb thin film thermal transport has a superdiffusion exponent, = 1.51 ± 0.23 and Lévy-Fourier transition length, rLF = 0.19 ± 0.13 µm. Both obtained values via Tempered Lévy indicates the quasi-ballistic transport phenomena in GaSb thin film. However, this frequency dependence of the cross-plane thermal conductivity will disappear in the presence of the 3%–20% ErSb nanoparticles. Another thermal transport mechanism, i.e. anisotropic thermal transport, can be observed in GaSb thin film. The ratio of in- to cross-plane thermal conductivity varies from ∼0.2 to ∼0.7 in the 0%–20% ErSb nanoparticles volume concentrations. Detailed temperature dependence of the in-plane thermal conductivity of ErSb:GaSb samples with 0%–20% are also included in the paper for the understanding of the scattering mechanism in the thin film thermal transport. With enhanced understanding of the quasi-ballistic and anisotropic thin film thermal transport, our results might improve the thermal management efficiency of the GaSb devices. [ABSTRACT FROM AUTHOR]

Refractory materials have wide applications due to their high thermal and chemical stability. In this work, we numerically design the plasmonic structure for perfect light absorption using the resonant behaviours for these materials. The results of the simulation are presented using the three-dimensional finite-difference time-domain method. The maximum absorption reaches 99.9% and the near-unity absorption window spans a bandwidth of 1182 nm from 413 nm in the visible to 1595 nm in the near-infrared range. Strong plasmonic near-field coupling between the adjacent parts in the split circular Ti resonator and their coupling to the plasmon resonances of the TiN layer are the main reasons for the ultra-broadband perfect absorption. Moreover, the absorption is observed to be incident angle insensitive and polarization independent. Absorption properties can be manipulated via tuning the structural parameters. These impressive absorption features and the high thermal stability can have wide applications in the high-intensity or extreme condition operation such as laser pumping and nonlinear optics, and solar related technologies including thermal steam generation and desalination of seawater. [ABSTRACT FROM AUTHOR]

We report on a global crossover saturated-absorption spectroscopy (SAS) of Cs D2 transition using a dual-frequency laser field with a frequency difference of less than the Doppler width. With two pairs of dual-frequency laser beams counter-propagating through the vapor cell, the line shape and non-linear features observed in the transmission spectra of the probe beam change with the frequency difference of the dual-frequency laser. The superficially complicated transmission signal includes two sets of common single-frequency SAS and several velocity-selective resonances (VSRs), we call these VSR peaks 'global crossover SAS'. This phenomenon is explained by VSR effect. The global crossover SAS is formed by the atomic velocity groups resonance with both the initial and modulated laser fields, which are counter-propagated. Moreover, the global crossover SAS dips having the separation of allowed hyperfine transitions move along with the two sets of common single-frequency SAS while the frequency difference of the dual-frequency laser is changed. This indicates a resonance between the velocity shifted pump laser frequency and the velocity shifted probe laser frequency. The results obtained in this system are of great interest for laser spectroscopy. Furthermore, the application of the counter-propagating laser beams in the dual-mode regime increase the number of atoms that effectively interact with the field, hence, this scheme has a potential advantage for laser frequency stabilization. [ABSTRACT FROM AUTHOR]

We theoretically explore optical bistability for the possible signature of all-optical switching and their performance in a hybrid quantum optomechanical system comprising of two semiconductor microcavities coupled optically. One of the cavity is driven by an external amplitude-modulated pump laser while the second cavity, which contains a quantum dot (QD), is indirectly driven by light transmitted from the first cavity and a transverse optical field. The generated bistable behavior due to optomechanical nonlinearity shows a typical optical switching behavior and it can be controlled by changing the laser power, QD cavity coupling, modulating amplitude/frequency and the optomechanical coupling. A clear signature of energy exchange between the mechanical and optical modes is visible from the mechanical displacement spectrum. These results suggest that the present system can be used in sensitive optical switches and optical sensors. [ABSTRACT FROM AUTHOR]

We present a systematic study on the control of Cooper minimum (CM) in the high-order harmonics spectra generated during the interaction of Ar gas with ultrashort near-infrared laser pulses. Tailoring the width and depth of CM in argon is demonstrated by changing the gas jet position with respect to the focal plane of focusing lens and by defocusing-assisted phase-matching. We further analyze the influence of single- and two-color laser pump schemes on the appearance of CM. The application of two orthogonally-polarized fields of fundamental radiation and its second harmonic, which is also used to generate controllable yields of odd and even harmonics, led to diminishing the CM in the harmonic spectra. Our experimental findings are supported by theoretical calculations that solve the time-dependent Schrödinger equation in the microscopic domain, and take into account the phase matching in the macroscopic domain. [ABSTRACT FROM AUTHOR]

Optical-field ionization (OFI) is often used to produce plasmas for myriad laboratory applications. OFI of gases is known to generate electrons that have anisotropic distributions. In this paper we show that at the time of plasma formation the electron velocity distribution functions can be controlled by changing the wavelength and polarization of the pump laser and ionization state of the plasma. Thomson scattering is used to measure the distinct electron velocity distributions of helium plasmas produced by linearly and circularly polarized laser pulses within a few inverse plasma periods after the plasma formation. In both cases, nonthermal and highly anisotropic initial electron distributions are observed that are consistent with expectations from OFI of both He electrons. [ABSTRACT FROM AUTHOR]

The characteristics of terahertz (THz) radiation generated from large-aperture photoconductive antennas (LAPCAs) were investigated. The antennas were fabricated using different wide-bandgap semiconductor crystals (ZnSe, GaN, 6H–SiC, 4H–SiC and β–Ga2O3) as the substrate. We used an amplified sub-picosecond KrF excimer laser for illumination of the LAPCAs. THz emission scaling was studied as a function of the bias field and the pump laser energy. It was found that the radiated THz energy scales quadratically as a function of the bias field and sub-linearly as a function of the optical fluence for most of the substrates. Further, we demonstrate that SiC, and especially 4H–SiC LAPCAs offer the best THz generation performances. In order to generate intense THz radiation, we fabricated both 6H- and 4H–SiC LAPCAs with an interdigitated structure. From the field autocorrelation trace, it was found that the spectra lie in the sub-THz regime, extending up to 400 GHz, with a peak frequency at 50 GHz, making the bridge between the microwaves band and the THz band. The maximum generated THz energy was 11 μJ, which is to date the highest THz energy measured from LAPCA sources, with a corresponding peak electric field of 115 kV cm−1 and a corresponding ponderomotive potential of 60 eV. Nonlinear THz experiments were performed using these energetic THz pulses, and open aperture Z-scan experiments in an n-doped InGaAs layer revealed a transmission enhancement of 1.7. It was also shown that in order to have efficient THz generation, the energy contrast of the laser must be kept high. [ABSTRACT FROM AUTHOR]

Weinvestigate exciton-polariton condensates with a rotating potential induced by an electric field in a semiconductor microcavity ring. In the absence of transverse-electric-transverse-magnetic (TE-TM) splitting, we find that there is a critical laser pump rate, above which the quantized phase slips appear with hysteresis, and there exist quantized average angular momenta at fixed angular velocities, regardless of the pump rate. When considering the TE-TM splitting, we find that there are a series of hysteresis loops with the same intervals which are modulated by the magnitude of the splitting for a linear polarization laser. Further, multistability occurs at large pump rate, and there arises a phase slip for only one spin with large absolute value of the polarization degree, owing to the competition of the TE-TM splitting and energy induced by rotation. These results can be verified experimentally with current technology, and are useful for future electro-optic devices. [ABSTRACT FROM AUTHOR]

We report a spatially resolved photoluminescence mapping of InGaAs quantum wells. The photoluminescence was collected on top of the quantum well, with a HeNe laser pumping horizontally or vertically. In the horizontal configuration, at temperature of 68 K, the spectral linewidth narrows from 2.8 to 2.2 meV with the peak shifting from 1.4425 to 1.4415 eV, while at 3.8 K these changes were not observed. This demonstrates that photo-generated carriers can diffuse away from the laser spot and relax to the lower energy states in the case when the charge carriers are thermally activated. The spectra narrowing in the vertical configuration, which could not be observed, is due to the fact that the emitted light was always collected from the same spot of the pumping laser without diffusion. [ABSTRACT FROM AUTHOR]

We investigate the synthesis of a hyperfine spin lattice in an atomic Bose–Einstein condensate, with two hyperfine spin components, inside a one-dimensional high-finesse optical cavity, using off-resonant superradiant Raman scattering. Spatio-temporal evolution of the relative population of the hyperfine spin modes is examined numerically by solving the coupled cavity–condensate mean-field equations in the dispersive regime. We find, analytically and numerically, that beyond a certain threshold of the transverse laser pump, Raman superradiance and self-organization of the hyperfine spin components occur simultaneously and as a result a magnetic lattice is formed. The effects of an extra laser pump parallel to the cavity axis and the time dependence of the pump strength on the synthesis of a sharper lattice are also addressed. [ABSTRACT FROM AUTHOR]

In this paper, the theoretical rate equation model of an in-band pumped gain-switched thulium-doped fiber (TDF) laser is investigated. The analytical formulations of pump energy threshold, peak power extraction efficiency, and pulse extraction efficiency are derived through analyzing the interaction process between the pump pulse and the laser pulse. They are useful for understanding, designing, and optimizing the in-band pumped TDF lasers in a 1.9 µm-2.1 µm wavelength region. The experiment with an all-fiber gain-switched TDF laser pumped by a 1.558-µm pulse amplifier is conducted, and our experimental results show good agreement with theoretical analysis. [ABSTRACT FROM AUTHOR]

We present an active optical clock scheme with a four-level quantum potassium system. We calculate the population probabilities of each state using the density matrix. At the steady state, ?33 and ?55 are equal to 8.3% and 3.5%, respectively, and the population inversion between the 5S1/2 and 4P3/2 states is built up in the thermal potassium cell with a 404.7 nm pumping laser. According to the mechanism of the active optical clock, under the action of the 404.7 nm pumping laser, the scheme can output a 1252.2 nm quantum-limited-linewidth laser, which can be directly used as an active optical frequency standard. [ABSTRACT FROM AUTHOR]

Linewidth of a laser diode stack with 5 bar is reduced to 0.2 nm from 1.8 nm through the use of an external volume Bragg grating (VBG) cavity. The temperature of the VBG is controlled efficiently to make the central wavelength tunable. The linewidth changes little in the wavelength-tuning experiments. Since the tunable range covers the rubidium D2 absorption line, the stack can be used to pump the rubidium laser efficiently. [ABSTRACT FROM AUTHOR]

An efficient dual-wavelength laser-diode-pumped Nd:YAG ceramic laser operating at 1112 and 1116nm is demonstrated. We obtain a maximum total output power of 3.43 W including a 1.77W 1112nm component and a 1.66W 1116nm component under a pump power of 16.1 W, corresponding to a slope efficiency of 23.7% and a total optical-to-optical efficiency of 21.3%. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a high efficiency broadband near infrared single-photon upconversion and detection with a broadband pump laser based on sum frequency conversion in the PPLN crystal. By using a pump laser centered at 1040 nm with a spectral bandwidth of 10 nm, the signal single-photons centered at 1562 nm with a broadband bandwidth up to 7.2 nm are frequency-converted from the near infrared to the visible regime. A maximum conversion efficiency of 18.8% is achieved, while the background noise is measured to be only 1.2 × 10−3 counts/pulse. The corresponding spectral linewidth of the upconverted photons is 0.2 nm. This scheme of broadband infrared single-photon upconversion and detection provides potential solutions in infrared laser ranging, broadband infrared imaging and quantum key distribution. [ABSTRACT FROM AUTHOR]

We demonstrate that the etalon effects of alkali cells can be used as the output coupler of an alkali laser. Based on a rubidium cell with highly parallelized windows, a 2.7 W rubidium laser with optical efficiency of 20.9% and slope efficiency of 31.8% is obtained by adopting unconventional output couplers. Since it has compact configuration and the inner surface of the rubidium cell is uncoated, this may be used in high power laser systems with long lifetimes. [ABSTRACT FROM AUTHOR]

A theoretical study for femtosecond laser-induced ultrafast electro-absorption of bulk solids is presented. Our numerical results show that, in the case of low intensity of the pump laser where the interaction between the pump laser and solids is in the multi-photon regime, the energy band of solids can be approximately taken as a parabolic band and electro-absorption spectrums from the parabolic band and real band are nearly the same. While, in the case of high intensity where the interaction is in the tunneling regime, spectrums from the parabolic band and real band are quite different. The physical mechanism for the difference in the tunneling regime is found. We find that the non-parabolic parts of the real energy band and Bragger scattering of electrons near the first Brillouin zone boundaries, which are neglected in previous studies, strongly influence the electro-absorption spectrum in the tunneling regime. These two physical processes cause the difference of spectrums. Our theoretical results are in accordance with the experiment result. [ABSTRACT FROM AUTHOR]

The paper presents the experimental results of a study of higfh-power laser diodes with a surface distributed Bragg reflector of 13-th and 16-th diffraction order emitting at a wavelength of 1026 nm and 1050 nm in a continuous and pulsed pump mode. The effect of the high-order DBR groove shape on the diffraction efficiency of high diffraction orders—parasitic output optical losses—has been experimentally studied. It is shown that the design of a laser resonator with a low reflective output short DBR can significantly reduce the parasitic losses and increase the laser efficiency while maintaining spectrally selective features over the entire range of pump currents. It was shown that pulse pumping (2–100 ns) does not impair the spectral selectivity of the high-order DBR and ensures a laser line width of 0.3 nm even in the range of high pump levels (50 A/1 00 ns). Investigations of a pulsed 2 ns time-resolved laser pump demonstrated that there is no influence of the electrically passive absorbing section of the DBR on the shape of the optical pulse. [ABSTRACT FROM AUTHOR]

A femtosecond LBO optical parametric oscillator (OPO) with widely adjustable repetition rate by fractionally decrement of the cavity length is demonstrated. The repetition rate of 755MHz to 1.43 GHz at an interval of 75.5MHz is realized, which is 10 to 19 times that of the pump laser. The properties of output signal at 750nm at different repetition rates are studied. The power of signal decreases with increasing the repetition rate. The maximum power of 194mW at the repetition rate of 755MHz and the minimum power of 22mW at repetition rate of 1.43 GHz for the signal at 750nm are obtained for the pump power of 3 W. [ABSTRACT FROM AUTHOR]

Electrospinning is a very simple method of preparing polymer solutions into high performance fibers. In this work, PM597-doped polymer fibers with different diameters have been fabricated by electrospinning technology. Whispering gallery mode (WGM) lasing emission was observed when a 532 nm pulse laser beam radially excited the single electrospun polymer fiber (EPF) created by this method. The distribution of WGMs is also quantitatively confirmed through theoretical calculation. Additionally, the number of WGM laser peaks decrease as the diameter of the EPF decreases. Single longitudinal mode laser emission can be obtained when the EPF diameter decreases to 8.8 µm. It has also been found that the WGM laser from the single EPF has relatively low thresholds and good lifetime compared to droplet lasers or other fiber lasers. Moreover, EPF networks have unique research prospects in photonic devices, optical pump lasers and biosensing due to their very large surface to volume ratio. [ABSTRACT FROM AUTHOR]

We presented a passively Q-switched (PQS) diode-pumped c-cut Tm, Ho:LuVO4 laser with a black phosphorus saturable absorber for the first time. Under PQS mode, an average output power of 0.86 W and a peak power of 2.32 W were acquired from the Tm, Ho:LuVO4 laser with the pump power of 14.55 W, corresponding to a pulse width of , a pulse repetition rate of 71.84 kHz, and a pulse energy of about . [ABSTRACT FROM AUTHOR]

We report herein a high-power folded intra-cavity 2.1 μm optical parametric oscillator (ICOPO) which is the first example of an ICOPO that utilizes a wavelength-locked 878.6 nm in-band pumped Nd:YVO4 laser as the pump source. The thermal effect of PPMgLN crystal and the divergence angle of the incident laser are considered comprehensively to determine the 2128 nm degenerate temperature. In the experiment, the functions of different output coupler transmittances and different repetition rates on the parametric laser output power are studied, respectively. The temperature versus parametric laser output power in an in-band pumped non-wavelength-locked 880 nm laser diode (LD) and in a wavelength-locked 878.6 nm LD is compared. A maximum output power of 5.87 W is obtained at the pump power of 56.9 W when the repetition rate is 80 kHz. The corresponding conversion efficiency is 14.55%, with a linewidth of 73.65 nm and pulse width of 3.62 ns. The wavelength-locked 878.6 nm LD in-band pumping technology can stabilize the 2.1 μm laser output power of Nd:YVO4 crystal effectively in the environment of intense temperature change. [ABSTRACT FROM AUTHOR]

We experimentally investigate the continuous-wave (cw) and acousto-optical (AO) Q-switched performance of a diode-pumped Ho:(Sc0.5Y0.5)2SiO5 (Ho:SYSO) laser. A fiber-coupled laser diode at 1.91 μm is employed as the pump source. The cw Ho:SYSO laser produces 13.0 W output power at 2097.9 nm and 56.0% slope efficiency with respect to the absorbed pump power. In the AO Q-switched regime, at a pulse repetition frequency of 5 kHz, the Ho:SYSO laser yields 2.1 mJ pulse energy and 21 ns pulse width, resulting in a calculated peak power of 100 kW. In addition, at the maximum output level, the beam quality factor of the Q-switched Ho:SYSO laser is measured to be about 1.6. [ABSTRACT FROM AUTHOR]

We demonstrated an Fe:ZnSe laser pumped by a 2.93- Cr, Er:YAG laser at liquid nitrogen and room temperature in single-shot free-running operation for the first time. The xenon flash lamp pumped Cr, Er:YAG laser had a maximum single pulse energy of 1.414 J, and the threshold and slope efficiency were 141.70 J and 0.70% which were respectively reduced by 29.3% and increased by 52.2% compared with the Er:YAG laser. At liquid nitrogen temperature of 77 K, the maximum single pulse energy of the Fe:ZnSe laser was 197.6 mJ, corresponding to a slope efficiency of 13.4%. The central wavelength and full width at half maximum (FWHM) linewidth were 4037.4 nm and 122.0 nm, respectively. At room temperature, the laser generated a maximum single pulse energy of 3.5 mJ at the central wavelength of 4509.6 nm with an FWHM linewidth of 171.5 nm. [ABSTRACT FROM AUTHOR]

Highly nonlinear fibers (HNLFs) are crucial components for supercontinuum (SC) generation with laser solution. However, it is difficult to exactly estimate the structure of produced SC according to material parameters. To give a guideline for choosing and using HNLFs for erbium-fiber-based optical applications, we demonstrate SC generation in five types of HNLFs pumped by 1.57- laser solitons. All five fibers output a SC exceeding 1000 nm. Three different SC formation processes were observed in the experiment. By comparing optical parameters of these fibers, we find the zero dispersion wavelength (ZDW) of fiber has an important influence on the SC structure and energy distribution for a given pump source. [ABSTRACT FROM AUTHOR]

We demonstrate a gain-switched Fe:ZnSe laser pumped by a 2958 nm pulsed Ho,Pr:LLF laser. The maximum single pulse energy is 16.4 μJ with a minimum pulse duration of 13.9 ns at the pulse repetition frequency of 1 Hz when the Fe:ZnSe crystal is cooled to 77 K by liquid nitrogen, corresponding to a slope efficiency of 22.9%. The central wavelength and FWHM linewidth are 3957.4 nm and 23.2 nm, respectively. The output energy monotonically decreases as the crystal temperature increases in the range 77–293 K. [ABSTRACT FROM AUTHOR]

With increasing output power, stimulated Raman scattering (SRS) becomes one of the main limitations for high power fiber laser oscillators. In this work, the SRS threshold dependence on the bandwidths of fiber Bragg gratings (FBGs) has been experimentally investigated in co-pumped and counter-pumped ytterbium-doped all-fiber laser oscillators, respectively. In both co-pumped and counter-pumped laser oscillators, FBGs with respective bandwidths of 0.24 nm, 0.5 nm, 1 nm and 2 nm are used as the output coupler. It is found that with the increasing bandwidth of the output-coupler FBG (OC-FBG), the SRS threshold of the laser oscillator also increases and when the bandwidth of the OC-FBG reaches over ∼1 nm, the SRS threshold increases slowly. Compared with co-pumping configuration, a counter-pumped laser oscillator holds a higher SRS threshold when the same OC-FBG is applied. By employing a counter-pumping configuration and increasing the bandwidth of the OC-FBG to 2 nm, the output laser power is further scaled to 3 kW-level with a slope efficiency of 70%. The M2 factor is measured to be ∼1.3 at the maximum output power. [ABSTRACT FROM AUTHOR]

A novel flat–flat resonator consisting of two crystals (Nd:YAG + Nd:YVO4) is established for power scaling in a diode-end-pumped solid-state laser. We systematically compare laser characteristics between multi-segmented (Nd:YAG + Nd:YVO4) and conventional composite (Nd:YAG + Nd:YAG) crystals to demonstrate the feasibility of spectral line matching for output power scale-up in end-pumped lasers. A maximum continuous-wave output power of 79.2 W is reported at 1064 nm, with , , and a pumping power of 136 W in the multi-segmented crystals (Nd:YAG + Nd:YVO4). Compared to conventional composite crystals (Nd:YAG + Nd:YAG), the optical-optical conversion efficiency of multi-segmented crystals (Nd:YAG + Nd:YVO4) from 808 nm to 1064 nm is enhanced from 30% to 58.8%, while the laser output sensitivity as affected by the diode-laser temperature is reduced from 55% to 9%. [ABSTRACT FROM AUTHOR]

This paper reports the plasmonic lasing of a split ring filled with gain material in water. The lasing mode (1500 nm) is far from the pump mode (980 nm), which can depress the detection noise from the pump light. The laser intensities of the two modes simultaneously increase by more than 103 in amplitude, which can intensify the absorption efficiency of the pumping light and enhance the plasmonic lasing. The plasmonic lasing is a sensitive sensor. When a single protein nanoparticle (n = 1.5, r = 1.25 nm) is trapped in the gap of the split ring, the lasing spectrum moves by 0.031 nm, which is much larger than the detection limit of 10−5 nm. Moreover, the lasing intensity is also very sensitive to the trapped nanoparticle. It reduces to less than 1/600 when a protein nanoparticle (n = 1.5, r = 1.25 nm) is trapped in the gap. [ABSTRACT FROM AUTHOR]

One of the peculiar phenomenons in non-zero magnetic resonance magnetometer is that, with the increase of the temperature, the magnetic resonance linewidth is narrowed at first instead of broadened due to the increasing collision rate. The magnetometer usually operates at the narrowest linewidth temperature to obtain the best sensitivity. Here, we explain this phenomenon quantitatively considering the nonlinear of the optical pumping in the cell and did experiments to verify this explanation. The magnetic resonance linewidth is measured using one amplitude-modulated pump laser and one continuous probe laser. The field is along the direction orthogonal to the plane of pump and probe beams. We change the temperature from 53 °C to 93 °C and the pumping light from 0.1 mW to 2 mW. The experimental results agree well with the theoretical calculations. [ABSTRACT FROM AUTHOR]

In this paper, a reflective optical pump-probe technique for laser-driven plasmas at solid density target surfaces is presented. The technique is termed high depth-of-field time-resolved microscopy and it exploits the angular redistribution of the probe beam intensity after the probe’s reflection from an expanded and hence non-planar iso-density surface in the plasma. The main application of the robust technique, which uses simple imaging of the probe beam, is the spatio-temporal resolution of the plasma formation and expansion at the target rear surface. Analytic and numerical modeling of the experimental setup are applied for the analysis of the experimental results. The relevance and potential of the optical plasma probing method is highlighted by the application to targets of different geometries, helping to understand the target shape-related differences in the ion acceleration performance. [ABSTRACT FROM AUTHOR]

A simultaneous dual-wavelength intracavity pumped non-critical eye-safe optical parametric oscillator (OPO) is realized using a Nd:GYSGG laser crystal and a KTP nonlinear crystal. A folded cavity is used for thermal stability and mode matching, which greatly improves the output characteristics versus a linear cavity. The maximum output power of the 1562.1 nm/1567.4 nm dual-wavelength eye-safe laser is 750 mW at 10 kHz, corresponding to the optical-to-optical conversion efficiency, single-pulse-energy and peak power of 5.8%, 75 μJ and 22.7 kW. Such a dual-wavelength OPO provides a good laser source for remote sensing for CO and CO2 gases or difference frequency generation for terahertz wave at the important 0.65 THz band. [ABSTRACT FROM AUTHOR]

We demonstrate a widely tunable near-infrared source from 767 nm to 874 nm generated by the intracavity second harmonic generation (SHG) in an optical parametric oscillator pumped by a Yb:LYSO solid-state laser. The home-made Yb:LYSO oscillator centered at 1035 nm delivers an average power of 2 W and a pulse duration as short as 351 fs. Two MgO doped periodically poled lithium niobates (MgO:PPLN) with grating periods of 28.5–31.5 μm in steps of 0.5 μm and 19.5–21.3 μm in steps of 0.2 μm are used for the OPO and intracavity SHG, respectively. The maximum average output power of 180 mW at 798 nm was obtained and the output pulses have pulse duration of 313 fs at 792 nm if a sech2-pulse shape was assumed. In addition, tunable signal femtosecond pulses from 1428 nm to 1763 nm are also realized with the maximum average power of 355 mW at 1628 nm. [ABSTRACT FROM AUTHOR]