Broadband Laser Research Articles

Efficient Electronic Excitation Transfer via Phonon-Assisted Dipole-Dipole Coupling inFe2+:Cr2+:ZnSe

${\mathrm{Cr}}^{2+}$ - and ${\mathrm{Fe}}^{2+}$ -doped $\mathrm{Zn}\mathrm{Se}$ crystals are laser materials with phonon-broadened absorption and emission spectra, which provide broadband laser gain in the 2- to 5-$\text{\ensuremath{\mu}}\mathrm{m}$ wavelength range. While ${\mathrm{Cr}}^{2+}\text{:ZnSe}$ can be directly pumped with high-power Er, Ho, or Tm lasers, no such possibility exists for ${\mathrm{Fe}}^{2+}\text{:ZnSe}$. To this end, electronic excitation transfer between ${\mathrm{Cr}}^{2+}$ and ${\mathrm{Fe}}^{2+}$ ions in codoped ZnSe is investigated as an alternative excitation process in photo luminescence (PL) experiments with sub-10-ns temporal resolution. For a wide range of ion concentrations, we observe nonexponential decays of ${\mathrm{Cr}}^{2+}$ PL on a microsecond time scale, a 60-ns rise time of ${\mathrm{Fe}}^{2+}$ PL at high doping densities, and a prolonged decay of ${\mathrm{Fe}}^{2+}$ PL due to the temporal characteristics of excitation transfer over a range of interionic distances. Using a multirate equation model, the transfer process is analyzed on length scales up to 30 nm and compared to the established continuum model approach. The analysis reveals an unexpectedly efficient excitation transfer from ${\mathrm{Cr}}^{2+}$ to ${\mathrm{Fe}}^{2+}$ ions with an enhancement of the excitation transfer rates by up to a factor of 5 in comparison to resonant dipole-dipole coupling. The enhancement is assigned to (multi)phonon-assisted excitation transfer, in analogy to the phonon-mediated efficient radiationless decay of the excited ${\mathrm{Fe}}^{2+}$ state. As nonradiative losses and excitation transfer show different temperature scaling, a cryogenic temperature regime is found that promises overall efficiencies above 50%, making ${\mathrm{Fe}}^{2+}:{\mathrm{Cr}}^{2+}\text{:ZnSe}$ a much more viable alternative to parametric conversion schemes in the midinfrared range.

Microcantilever-integrated photonic circuits for broadband laser beam scanning

Laser beam scanning is central to many applications, including displays, microscopy, three-dimensional mapping, and quantum information. Reducing the scanners to microchip form factors has spurred the development of very-large-scale photonic integrated circuits of optical phased arrays and focal plane switched arrays. An outstanding challenge remains to simultaneously achieve a compact footprint, broad wavelength operation, and low power consumption. Here, we introduce a laser beam scanner that meets these requirements. Using microcantilevers embedded with silicon nitride nanophotonic circuitry, we demonstrate broadband, one- and two-dimensional steering of light with wavelengths from 410 nm to 700 nm. The microcantilevers have ultracompact ~0.1 mm2 areas, consume ~31 to 46 mW of power, are simple to control, and emit a single light beam. The microcantilevers are monolithically integrated in an active photonic platform on 200-mm silicon wafers. The microcantilever-integrated photonic circuits miniaturize and simplify light projectors to enable versatile, power-efficient, and broadband laser scanner microchips.

A new near-infrared broadband laser crystal: Cr3+ doped YScO3

A new near-infrared broadband laser crystal: Cr3+ doped YScO3

Suppressing parametric instabilities in direct-drive inertial-confinement-fusion plasmas using broadband laser light

It has long been recognized that broadband laser light has the potential to control parametric instabilities in inertial-confinement-fusion (ICF) plasmas. Here, we use results from laser-plasma-interaction simulations to estimate the bandwidth requirements for mitigating the three predominant classes of instabilities in direct-drive ICF implosions: cross-beam energy transfer (CBET), two-plasmon decay (TPD), and stimulated Raman scattering (SRS). We find that for frequency-tripled, Nd:glass laser light, a bandwidth of 8.5 THz can significantly increase laser absorption by suppressing CBET, while ∼13 THz is needed to mitigate absolute TPD and SRS on an ignition-scale platform. None of the glass lasers used in contemporary ICF experiments, however, possess a bandwidth greater than 1 THz and reaching larger values requires the use of an auxiliary broadening technique such as optical parametric amplification or stimulated-rotational-Raman scattering. An arguably superior approach is the adoption of an argon-fluoride (ArF) laser as an ICF driver. Besides having a broad bandwidth of ∼10 THz, the ArF laser also possesses the shortest wavelength (193 nm) that can scale to the high energy/power required for ICF—a feature that helps to mitigate parametric instabilities even further. We show that these native properties of ArF laser light are sufficient to eliminate nearly all CBET scattering in a direct-drive target and also raise absolute TPD and SRS thresholds well above those for broadband glass lasers. The effective control of parametric instabilities with broad bandwidth is potentially a “game changer” in ICF because it would enable higher laser intensities and ablation pressures in future target designs.

Rotation of the polarization ellipse for broad-band and narrow-band optical pulses. Analytical solutions

In present days the evolution of broad-band laser pulses, propagating in various types of waveguides, has been of a great interest among the scientists. Currently, it is easy for phase-modulated femtosecond pulses the condition Δω≈ω0 to be obtained. It is known that nowadays it is possible also to reach the attosecond region where the spectral bandwidth of the pulse happens to be of order of the carrier frequency also. Light pulses who fulfil this initial condition are called broad-band. On the other hand, the non-fulfilling pulses are the narrow-band ones.In the present paper it is investigated the parametric interaction of two components of one optical pulse by using the Generalized System of Nonlinear Amplitude Equations (GSNAE). GSNAE was analytically solved. A difference in the period of oscillations of the energy exchange between the two components is found.

Suppression of stimulated Raman scattering in plasma by an ultra-wideband stochastic phase low-coherence laser

Suppression of the stimulated Raman scattering (SRS) by a stochastic phase low-coherence laser (SPLL) in homogeneous plasma is investigated by theoretical analysis and one-dimensional particle-in-cell (PIC) simulation. A simple model is established, in which the SPLL is modelled as a combination of a monochromatic laser and a broadband laser. When the phase randomness increases, the bandwidth of the SPLL is broadened and the energy proportion of the monochromatic laser component is reduced. PIC simulation shows that the SPLL can effectively suppress SRS and hot electron generation. Various phenomena in the nonlinear process, such as the nonlinear frequency shift and the competition between forward-scattering and back-scattering modes, are explained in detail.

Enhanced broadband NIR emission in glass–ceramic fibers containing Nd3+/Yb3+ co‐doped YCa4O(BO3)3 disordered nanocrystal

AbstractDemands are increasing for ultrashort pulse laser in industrial applications, where the gain bandwidth of most optical fiber material is not wide enough, and developing a wide bandwidth gain medium is challenging. Glass–ceramic fibers containing Nd3+/Yb3+ co‐doped YCa4O(BO3)3 nanocrystals were fabricated by the molten core method and successive heat treatment. After a careful heat treatment, Nd3+/Yb3+ co‐doped YCa4O(BO3)3 nanocrystals were precipitated in the fiber core. Enhanced broadband near‐infrared (NIR) emission from 850 to 1150 nm (bandwidth: ∼252 nm) was obtained in the glass–ceramic fiber compared to that of precursor fiber. These results suggest that the Nd3+/Yb3+ glass–ceramic fibers are promising for broadband NIR optical amplifications and lasers.

Breath analysis by ultra-sensitive broadband laser spectroscopy detects SARS-CoV-2 infection

Rapid testing is essential to fighting pandemics such as coronavirus disease 2019 (COVID-19), the disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Exhaled human breath contains multiple volatile molecules providing powerful potential for non-invasive diagnosis of diverse medical conditions. We investigated breath detection of SARS-CoV-2 infection using cavity-enhanced direct frequency comb spectroscopy (CE-DFCS), a state-of-the-art laser spectroscopic technique capable of a real-time massive collection of broadband molecular absorption features at ro-vibrational quantum state resolution and at parts-per-trillion volume detection sensitivity. Using a total of 170 individual breath samples (83 positive and 87 negative with SARS-CoV-2 based on reverse transcription polymerase chain reaction tests), we report excellent discrimination capability for SARS-CoV-2 infection with an area under the receiver-operating-characteristics curve of 0.849(4). Our results support the development of CE-DFCS as an alternative, rapid, non-invasive test for COVID-19 and highlight its remarkable potential for optical diagnoses of diverse biological conditions and disease states.

Long Period Fiber Grating for Refractive Index Sensing

Refractive index (RI) sensors are very valuable in first level detection of changes to the environment. In this project an optical fiber-based sensor is proposed to detect changes in surrounding RI. Most optical fiber sensors require tapering to be done to enhance the light interaction with the surrounding. This causes the fiber to become fragile and difficult to handle. In this research, optical fibers with long period gratings (LPG) are proposed to overcome this issue. Zinc Oxide (ZnO) nanomaterial was deposited over the LPG region using seeding method to enhance the performance of the sensor. The LPG fiber sensor was then used to investigate RI changes in the environment. A broadband laser source was used as the input and an optical spectrum analyser was used to observe the output light spectrum of the LPG sensor for different refractive index mediums. The ZnO coated LPG showed a sensitivity of 428.57 nm/RIU over an RI range of 1 – 1.3578.

Ray-based cross-beam energy transfer modeling for broadband lasers

Broadband lasers have the potential to mitigate cross-beam energy transfer (CBET) in direct-drive inertial confinement fusion (ICF) experiments. A quantitative assessment of the bandwidth required for CBET mitigation necessitates the development of broadband ray-based CBET models that can be implemented in the radiation-hydrodynamic codes that are used to design ICF experiments. Two different approaches to broadband ray-based CBET modeling (discrete and fixed spectrum) are developed and compared to wave-based calculations. Both approaches give good agreement with wave-based calculations in ICF-relevant configurations. Full-scale 3D calculations show that the bandwidth required for adequate CBET mitigation increases with increasing scale and drive intensity.

An extended Vlasov–Fokker–Planck approach for kinetic simulations of laser plasmas

Vlasov–Fokker–Planck simulation codes occupy an important niche in modeling laser-produced plasmas, since they are well suited to studying the effect of collisions on electron kinetic phenomena, especially energy transport. One of the most important elements of energy transport is the absorption of laser light by the plasma; however, simulating this in detail requires resolving oscillations of the laser light, whose characteristic timescale is orders of magnitude shorter than the simulation time needed to study transport physics. For this reason, most Vlasov–Fokker–Planck codes used to study electron transport in laser plasmas rely on simplified models of the laser–plasma coupling. Their underlying assumptions nominally preclude their use for modeling laser light having short-scale structure in space or time, such as broadband lasers. In this work, we derive a more general computational framework suitable for arbitrarily structured laser fields. Our approach is based on an extended set of Vlasov–Fokker–Planck equations that separately solve for the low- and high-frequency plasma response. We implement these extended Vlasov–Fokker–Planck equations in the spherical harmonic code K2 and demonstrate the performance of the method on several laser absorption test problems, with particular attention to the judicious selection of time steps, time integrators, and spherical harmonic truncation, according to the intensity and spectrum of the laser light under consideration. Comparison with the widely used Langdon absorption operator shows the Langdon operator performs remarkably well for predicting laser heating in the simple cases considered here, even in situations that would seem to violate its underlying assumptions.

A 40-Gbps fiber-FSO convergent transmission system employing OFCL-based WDM and external modulation technique

We have proposed and demonstrated a 40Gbps fiber-free space optics (FSO) convergent system based on external modulation and wavelength division multiplexing (WDM) technique. In this experiment, 4010×4 Gbps signal is successfully transmitted employing WDM scheme over 50 km single mode fiber plus 2.5 km FSO distance. Optical frequency comb lines (OFCL) are generated using a continuous wave laser diode, a radio frequency signal generator, a dual drive Mach Zehnder modulator, and an electrical attenuator. OFC lines, having a side mode suppression ratio (SMSR) value of ∼40 dB and flatness of ∼0.4 dB, are employed as broadband laser source in the presented convergent system. The performance of the fiber-FSO system is investigated theoretically for different weather conditions. Very low power penalty with low bit error rate (BER), clear eye diagrams, and standard Q-factor are achieved in the proposed system. The power penalty is restricted within 2.5 dB and 5.8 dB at a BER of 10−9 for 50 km SMF plus 2.5 km FSO distance in clear weather and 50-km SMF plus 0.4-km FSO distance in heavy fog condition respectively. Thus, the proposed WDM-convergent system is efficient enough for high data rate transmission along with low BER value of ∼10−9 and high Q-factor for different environmental scenarios.

Dial Sounder of Methane Insusceptible to Variable Humidity Based on Broadband Laser Diodes

A novel differential absorption lidar method utilizing the spectral and energetic properties of pulsed, high-power, broadband laser diodes for remote sensing of methane is reported. The atmospheric gas content is retrieved using the derived calibration function, integrating multiple resonance lines of the selected CH4/Qyν3 second overtone absorption spectrum matched to a laser mode centred at optimal wavelength. The sensitivity of the lidar is effectively improved by multiplexation of the detected laser radiation in dual spectral channels eliminating the interference of the atmospheric water vapour.

Mode-modulation-induced high power dual-wavelength generation in a random distributed feedback Raman fiber laser.

An all-fiberized random distributed feedback Raman fiber laser (RRFL) with mode-modulation-induced wavelength manipulation and dual-wavelength generation has been demonstrated, where an electrically controlled intra-cavity acoustically-induced fiber grating (AIFG) is employed to adjust the input modal content at the signal wavelength. The wavelength agility of both the Raman effect and the Rayleigh backscattering in RRFL benefits on broadband laser output in case of broadband pumping. The feedback modal content at different wavelengths can be adjusted by AIFG, and then the output spectral manipulation can be ultimately manifested through the mode competition in RRFL. Under the efficient mode modulation, the output spectrum can be continuously tuned from 1124.3 nm to 1133.8 nm with single wavelength, while ulteriorly the dual-wavelength spectrum can be formed at 1124.1 nm and 1134.7 nm with a signal-noise-ratio of 45 dB. Throughout, the power is beyond 47 W with good stability and repeatability. To the best of our knowledge, this is the first dual-wavelength fiber laser based on mode modulation and the highest output power ever reported for an all-fiberized continuous wave dual-wavelength fiber laser.

The broadband laser source and an active beam stabilization device for laser calibration systems

The broadband laser source and an active beam stabilization device for laser calibration systems

Broad-band optical solitons

Current research is devoted to the study of the regimes of propagation of broad-band laser solitons with femtosecond or attosecond duration in isotropic nonlinear dispersive media such as single-mode optical fibers. Developments in this direction have been highly relevant in recent decades due to the increasing use of ultra-short laser technologies, where the optical pulses have duration of 5–6 fs, in scientific researches, which are not only of fundamental importance, but find application in various areas of public life, such as telecommunications, industry, medicine and many others.

Proposal for Zeeman slowing of Rb2 molecules in a supersonic beam, inducing internal cooling

We present a theoretical proposal on Zeeman slowing of a Rb2 supersonic beam, relying on transitions between rovibrational levels of the electronic ground-state and the electronic excited state. Translational cooling is induced by optical transitions from to involving P () and Q () branches. This is achieved by shaping the spectrum of broadband laser sources, in addition to two single-frequency laser sources addressing the transitions. Our Monte–Carlo simulations indicate that the velocity of the molecules can be slowed from 500 m s−1 down to a few m s−1 by a Zeeman slower with a 1.2 m length, after scattering about 150 000 photons. At the end of the slowing process, half of the molecules are internally cooled, predicted to be in the ground-state levels. A final optical pumping step transferring the population to the ground-state level could produce a molecular beam exiting the Zeeman slower which is cold in all the translational, vibrational, and rotational degrees of freedom. Such an approach could potentially be a great interest for cooling down a large class of molecular species.

Laser induced emission of NdAlO3 nanocrystals in vacuum, air, and liquid N2

The broadband laser induced white emission (LIWE) spectra of NdAlO3 nanocrystals in vacuum, air, and liquid N2 were explored. In particular, their dependence on excitation laser power was investigated. It was found that the LIWE spectra intensity increased exponentially the with laser power above the excitation threshold in all three cases. The process for NdAlO3 nanocrystals was discussed in terms of multiphoton ionization assisted by ejection of hot electrons. Two differences were observed depending on the conditions: the number of photons involved in the emission was higher in liquid N2 due to additional multiphoton ionization contribution of N2. Also, threshold value for LIWE showed an increasing behavior in air and liquid N2, discussed in terms of relative permittivity and thermal dissipation.

External-cavity diode laser-based near-infrared broadband laser heterodyne radiometer for remote sensing of atmospheric CO2.

A near-infrared broadband (1500-1640 nm) laser heterodyne radiometer (LHR) with a tunable external-cavity diode laser as the local oscillator is developed and the relative transmittance, which represents the absolute relationship between the measured spectral signals and the atmospheric transmittance, is derived. High-resolution (0.0087 cm-1) LHR spectra in the spectral region of 6248.5-6256 cm-1 were recorded for the observation of atmospheric CO2. Combined with the relative transmittance, the preprocessed measured LHR spectra, the optimal estimation method, and the Python scripts for computational atmospheric spectroscopy, the column-averaged dry-air mixing ratio of CO2 of 409.09 ± 8 ppmv in Dunkirk, France on February 23, 2019, was retrieved, which is consistent with GOSAT and TCCON data. The near-infrared external-cavity LHR demonstrated in the present work has a high potential for use in developing a robust, broadband, unattended, and all-fiber LHR for spacecraft and ground-based atmospheric sensing that offers more channel selection for inversion.

Growth and spectroscopic properties investigation of Er-doped BGSO single crystal: A potential gain medium for eye-safe laser

Erbium-doped crystals are well-suited for eye-safe solid-state laser systems around 1.5 μm. Broadband and high-gain Er-doped laser crystals can achieve high-power tunable laser output, which plays a great role in promoting commercial eye-safe laser research. Herein, the 2 at% Er-doped bismuth germanium silicate (BGSO) laser crystal is successfully grown by the vertical Bridgman method. The X-ray Rietveld refinement was used to obtain the structural parameters. The spectroscopic parameters of Er ions in BGSO crystal are calculated and analyzed with Judd-Ofelt theory. Furthermore, the broadband luminescence is observed in the wavelength range of 1450–1600 nm. The stimulated emission cross-section is calculated around 1500 nm, which largest value is 5.31 × 10−20 cm2 at 1543 nm. Meanwhile, the luminous efficiency of BGSO crystal in the eye-safe band is further characterized and explored by studying the energy transfer process and anomalous thermal quenching in the 550 nm and 660 nm bands. All results indicate that the Er: BGSO crystal is a promising broadband eye-safe laser material.