Diode-pumped Laser Research Articles

High-efficiency 5-watt wavelength-tunable UV output from an Alexandrite laser

We investigate the performance of continuous-wave wavelength-tunable ultraviolet output from a diode-pumped Alexandrite laser by intra-cavity second harmonic generation. At 385 nm, ultraviolet output power of 5.05 W is achieved which is the highest continuous-wave ultraviolet power to date for intra-cavity frequency doubled diode-pumped Alexandrite lasers and highest optical-to-optical efficiency of 16.2% is achieved with respect to absorbed red pump power. An excellent ultraviolet wavelength tunable range, 38 nm, is achieved from 364 nm to 402 nm. Cavity mode analysis is performed for design of the resonator including cavity analysis and the modelling of output power from this wavelength tunable ultraviolet laser.

Evaluating Nd3+:Na4Y6F22 single crystals as a promising active medium for diode-pumped lasers

The optical and spectroscopic properties and laser performances of Nd3+:Na4Y6F22 fluoride single crystals were systematically examined. The quasi-CW laser action in Nd3+:Na4Y6F22 disordered crystals was realized for the first time under 796 nm-diode pumping. The slope efficiency was 5.8 % with a lasing threshold approximately 19 mW in terms of absorbed pumping power. The reasons for the discrepancy between the promising spectral-kinetic characteristics and pure lasing efficiency under diode pumping were elucidated.

Random Raman Lasing in Diode-Pumped Multi-Mode Graded-Index Fiber with Femtosecond Laser-Inscribed Random Refractive Index Structures of Various Shapes

Diode-pumped multi-mode graded-index (GRIN) fiber Raman lasers provide prominent brightness enhancement both in linear and half-open cavities with random distributed feedback via natural Rayleigh backscattering. Femtosecond laser-inscribed random refractive index structures allow for the sufficient reduction in the Raman threshold by means of Rayleigh backscattering signal enhancement by +50 + 66 dB relative to the intrinsic fiber level. At the same time, they offer an opportunity to generate Stokes beams with a shape close to fundamental transverse mode (LP01), as well as to select higher-order modes such as LP11 with a near-1D longitudinal random structure shifted off the fiber axis. Further development of the inscription technology includes the fabrication of 3D ring-shaped random structures using a spatial light modulator (SLM) in a 100/140 μm GRIN multi-mode fiber. This allows for the generation of a multi-mode diode-pumped GRIN fiber random Raman laser at 976 nm with a ring-shaped output beam at a relatively low pumping threshold (~160 W), demonstrated for the first time to our knowledge.

Analytical study of the beam quality of a diode-pumped alkali laser with unstable resonator

Analytical model of Cs diode-pumped alkali laser with unstable confocal resonator is reported. Two of the parameters characterizing the quality of the output beam were studied: the axial luminous intensity in the far field and the power in the bucket (PIB). The far-field axial light intensity and PIB were compared with their values for a truncated Gaussian reference beam whose aperture was limited by the aperture of the large resonator mirror and 99% of the Gaussian beam energy passed through the aperture of this mirror. For large values of the unstable resonator magnification factor m > 5, the far-field axial light intensity is approximately 40% larger than that of the Gaussian reference beam. Analysis of the PIB curves showed that for large m > 5, the values of the integrated fractional encircled power within a sufficiently large diffraction angles for the unstable resonator exceed its values for the reference Gaussian beam.

Er3+/Tm3+ codoped CaF2 based oxyfluoroborosilicate glass-ceramics for fiber laser applications

Transparent Er3+/Tm3+ codoped CaF2 based oxyfluoroborosilicate glass-ceramics (BSEr1TmxGCs) with variable Tm3+ concentration were prepared through melt quench process followed by reheat treatment at 450 °C/1h. They were characterized through differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) Raman spectroscopy, near infrared (NIR) emission and luminescence decay. The formation of CaF2 nanocrystallites against oxyfluoroborosilicate glassy phase was confirmed by scanning electron microscopic (SEM) and hi-resolution transmission electron microscopic (HRTEM) studies. The NIR emission properties were investigated at 460 nm diode laser pumping. The applicability of BSEr1TmxGCs were examined by evaluating effective bandwidth (Δλeff), stimulated emission cross-section (σe), gain bandwidth (σe × Δλeff), figure of merit (σe × τR) and quantum efficiency (ηQE). The energy transfer efficiency (ηET), rate of energy transfer (WET) between Er3+ and Tm3+ and the rate of non-radiative transitions (WNR) were also calculated. The comparative NIR emission performance suggests that the BSEr1Tm1GC has proficiency for 1530 nm broadband fiber lasers and optical amplifiers in short wavelength and conventional wavelength (S + C) band communication window.

Diode-pumped Kerr-lens mode-locked Ytterbium-doped compositional mixed calcium aluminate laser

Diode-pumped Kerr-lens mode-locked Ytterbium-doped compositional mixed calcium aluminate laser

First Achievement of Yellow Laser Operation in Dy3+-Doped Borate Crystals.

Continuous-wave (CW) yellow lasers have been demonstrated successfully by using a GaN laser-diode (LD) pumping in borate crystals for the first time. The Dy3+:GdMgB5O10 (Dy:GMB) crystal with dimensions up to 33 × 19 × 15 mm3 is grown by the top-seeded solution growth method, and the polarized spectroscopic properties are investigated systematically at room temperature. The line strengths, Judd-Ofelt (J-O) intensity, spontaneous transition rates, fluorescence branching ratios, and radiative lifetimes are calculated in detail by the Judd-Ofelt theory. Under direct pumping of 452 nm LD, a compact continuous-wave yellow laser with a maximum output power of 628 mW and laser wavelength of 581 nm is generated based on a Y-cut Dy:GMB crystal. To our knowledge, it is not only the highest output power for yellow laser obtained in Dy3+-doped crystals but also the first yellow laser operation achieved by borate crystals under direct LD pumping. The results reveal that the Dy:GMB crystal is an optical material with important application prospects in yellow laser.

Growth and optical properties of high-concentration Ho3+ ion-doped Ba(Y1−xLux)2F8 crystal for mid-infrared laser application

30mol% Ho:BaY2F8 (Ho:BYF) and 30mol% Ho, 20mol% Lu:BaY2F8 (Ho:BYLF) crystals with monoclinic phase were prepared by the Bridgman technique. After introducing Lu3+ ions, the thermal property of Ho:BYLF crystal was improved without significantly shortening the 5I5 level lifetime of Ho3+ ion compared with Ho:BYF crystal. Under laser diode pumping at 889 nm, the emission peaks of both Ho:BYF and Ho:BYLF crystals in the range of 3–5 μm could be detected. The spectral parameters of the crystal are calculated in detail, and the cross sections of absorption, emission and gain are given. During laser pumping, the two crystals showed low pumping threshold, and Ho:BYF crystal obtained a maximum energy output of 5.22 mJ, while Ho:BYLF crystal tended to be saturated at 1 mJ due to the high concentration of Lu3+ ion. These two crystals show great application potential for laser operating in the mid-infrared range.

Phase-stabilised self-injection-locked microcomb

Microresonator frequency combs (microcombs) hold great potential for precision metrology within a compact form factor, impacting a wide range of applications such as point-of-care diagnostics, environmental monitoring, time-keeping, navigation and astronomy. Through the principle of self-injection locking, electrically-driven chip-based microcombs with minimal complexity are now feasible. However, phase-stabilisation of such self-injection-locked microcombs—a prerequisite for metrological frequency combs—has not yet been attained. Here, we address this critical need by demonstrating full phase-stabilisation of a self-injection-locked microcomb. The microresonator is implemented in a silicon nitride photonic chip, and by controlling a pump laser diode and a microheater with low voltage signals (less than 1.57 V), we achieve independent control of the comb’s offset and repetition rate frequencies. Both actuators reach a bandwidth of over 100 kHz, enabling phase-locking of the microcomb to external frequency references. These results establish photonic chip-based, self-injection-locked microcombs as low-complexity yet versatile sources for coherent precision metrology in emerging applications.

Electro-optic Q-switched Yb:YAG thin disk laser with widely continuously tunable pulse width at a stable output of over 80 W

We report an electro-optic Q-switched Yb:YAG thin disk laser with widely continuously tunable pulse width ranging from 16.4 to 432.2 ns. The tunability was achieved through a simple and convenient method by rotating both the Pockels cell and the quarter-wave plate at either identical or slightly different angles. Based on the 72-pass pump module and 224.4 W laser diode pumping source, a pulsed output of over 80 W was attained at a repetition rate of 100 kHz. The output power and output pulse train remained stable in the whole tuning range. The corresponding output power was 82.7 W and 84.4 W for the minimum and maximum pulse width, respectively. A model which was exceedingly more accurate than previous models describing the tunability of the pulse width were proposed and the simulation results of this model exhibited strong agreement with the experimental measurements.

Modeling and analysis of single-mode widely tunable all-fiber Ho-doped CW master oscillator power amplifier system

We report the design of an all-fiber single-mode polarization maintaining widely tunable Ho-doped master oscillator power amplifier (MOPA) system operating in the wavelength range of 2005-2135 nm based on a pre-amplifier and two power amplification stages. The single clad Ho-doped active fibers in the ring cavity based master oscillator, pre-amplifier, and power amplifiers are pumped using 1950 nm semiconductor laser diode pump sources. The amplification of the MOPA system is investigated over the entire spectral range of 2005-2135 nm. The highest output power achieved by the continuous wave (CW) Ho-doped MOPA system is 43 W at a wavelength of 2028.6 nm using pump power of 20 W with power conversion efficiency (PCE) of 90% for second power amplifier while the total pump power of Ho-doped MOPA system is 45 W. Optical bandpass filters (OBPFs) are employed between different stages of MOPA system to enable amplification over the wider spectral range of 2005-2135 nm by suppressing the amplified spontaneous emission (ASE). Not using OBPFs results in amplification that is limited to the spectral range of 2045-2130 nm. Therefore, a penalty of 45 nm can be avoided at the expense of using the OBPFs between different stages of MOPA system. This flexible MOPA system can be used in multiple applications, especially for space-borne high power transmitters operating in atmospheric transmission windows.

Single-frequency orbital angular momentum switchable modes from a microchip laser.

We demonstrate the direct generation of single-frequency switchable orbital angular momentum (OAM) modes in a 1 µm wavelength range using a Nd:YVO4 microchip laser. The 808 nm laser diode pump beam is shaped into annular through an axicon associated with a lens. By adjusting the diameter and power of the annular pump beam, various OAM modes with different mode volumes can oscillate inside the Nd:YVO4 microchip. Moreover, a single-frequency output is also available due to the short cavity of the microchip. In the proof-of-principle experiment, single-frequency twofold multiplexed OAM modes | ± 1> and | ± 2> are generated, with experimentally measured fidelity higher than 96%. This work presents a compact and versatile single-frequency OAM source and will inspire multiple advanced scenarios ranging from classical to quantum photonics.

High energy and high repetition rate QCW-LD end-pumped electro-optical Q-switched Yb:YAG laser

The quasi-continuous wave laser diode (QCW-LD) pumping is considered as the most efficient way for generating high energy nanosecond pulsed laser with repetition rate ranging from 50 to 1000 Hz. Here, a high efficiency, high repetition rate and high energy QCW-LD end-pumped electro-optical (EO) Q-switched Yb:YAG laser was demonstrated. The shortest pulse duration of 17.4 ns with a maximum single pulse energy of 5.1 mJ was obtained at the repetition rate of 100 Hz. As the repetition rate increases up to 500 Hz, the maximum output single pulse energy was obtained to be 5.38 mJ with the pulse width of 18.7 ns, corresponding to the slope efficiency of 21.6% and beam quality factor of M x 2=1.04, and M y 2=1.01. In addition, a theoretical study was carried by numerical simulation of the rate equations, and the results were agreed well with the experimental ones. The results show that QCW-LD pumping with Yb-doped crystals is a promising way for highly efficient, high-energy and high repetition rate nanosecond pulsed laser generation.

Toward an understanding of the role of structural organization and point defects in the formation of functional pure and Tm3+-doped (Ca3-xSrx)(VO4)2 for diode-pumped and SRS lasers

Whitlockite-type polycrystalline and single-crystal (Ca3−xSrx)(VO4)2 solid solutions were successfully obtained by solid-state synthesis and Czochralski method, respectively. Synchrotron powder X-ray diffraction allowed to reveal actual compositions of polycrystalline (Ca3−xSrx)(VO4)2 solid solutions with х = 0.3, 0.54, 0.9, 1.2, 1.35 refined by Rietveld method, which are slightly different from the initial ones. Synchrotron X-ray single-crystal diffraction analysis of Czochralski-grown undoped (Ca1.8Sr1.2)(VO4)2 (CSVO) revealed its actual composition (Ca2.982(11)Sr0.031)(VО4)2. Difference between initial and refined compositions is analyzed and discussed. In the CSVO structure, Sr2+ ions partially occupy monocapped Ca2 and two-capped Ca3 trigonal prismatic sites and Ca2+ ions are in the Ca5 and Ca5A sites, forming two independent strongly distorted tetrahedral Ca5O4 and octahedral Ca5AO6 oxygen environments. Synchrotron X-ray single-crystal diffraction analysis together with X-ray absorption spectroscopic study of (Сa2.4Sr0.6)(VO4)2 doped with 0.5 and 1.0 wt% Tm2O3 (СSVO:0.5Tm and CSVO:1.0Tm) allowed to establish the absence of cations in the Ca5A site, the localization of Sr2+ ions in the Ca2 and Ca3 sites and additionally in octahedral Ca4 site together with Tm3+ ions, forming an individual eight-coordinated environment, in the refined compositions (Ca2.776(7)Sr0.210(4)Tm3+0.008(1))(VO4)2 and (Ca2.855(7)Sr0.140(7)Tm3+0.009(1)□0.022(7))(VO4)2, respectively, with vacancies (marked by a square,□) in the two-capped Ca1 trigonal prismatic site in the CSVO:1.0Tm structure. Additional interstitial oxygen, participating in the formation of the Tm3+ environment, found in the residual electron density, together with vacancies in the Ca1 site provides electroneutrality to CSVO:0.5Tm and CSVO:1.0Tm crystals. Several structural models of the coordination environment of Tm3+ ions were analyzed and the most correct one was proposed.

Double-Cycle Alternating-Flow Diode Pumped Potassium Vapor Laser

A novel double-cycle alternating-flow diode-pumped potassium vapor laser is proposed, theoretically modeled and simulated. The results show that the optical-to-optical efficiency of the laser increases with increasing gas flow rates, although at high flow rates the rate of increase in efficiency decreases. The optical-to-optical efficiency reaches 74.8% at a pump power density of 30 kW/cm2 and a gas flow rate of 50 m/s. The optical-to-optical efficiency of the laser is greater with a narrow linewidth pump and high buffer gas pressure. The optical-to-optical efficiency of a flow gas cell is higher than that of a static gas cell. There is an optimal gas cell length that provides the highest optical-to-optical efficiency. At higher pump power densities, higher flow rates are required to obtain higher optical-to-optical efficiencies.

High-power 2.3 µm Tm:YLF laser with intracavity upconversion pumping by a Nd:ASL laser at 1051 nm.

A Tm:LiYF4 laser operating on the 3H4 → 3H5 transition is embedded in a high-power diode-pumped Nd:ASL laser for intracavity upconversion pumping at 1.05 µm. This leads to a record-high output power at 2.3 µm for any bulk thulium laser pumped by an upconversion process. The continuous-wave Tm:LiYF4 laser delivers 1.81 W at 2.3 µm for 32 W of laser-diode pump power, making this kind of pumping competitive with direct diode pumping. The intracavity pumping process allows for counteracting the low absorption inherent to upconversion pumping and to dispatch the thermal loads on two separate laser crystals. The proposed laser architecture also features a relatively weak heating of the Tm:LiYF4 crystal and an increased tolerance to Tm3+ absorption. This laser design opens a new paradigm that holds great promise for high-power 2.3-µm solid-state lasers based on thulium ions.

Structural Properties, Energy Interaction, and Applications of CdS Nanomaterial Doped with Rare‐Earth Ions

AbstractSpectroscopic analysis of trivalent praseodymium (Pr+3) and neodymium (Nd+3) ions have received very much interest and reveals good fluorescence efficiency in visible and near IR (NIR) region. Cadmium sulfide (CdS) nanomaterial sample doped with Pr+3 and Nd+3 ions are synthesized at room temperature by simple chemical precipitation method. The synthesized sample has been characterized by powder X‐ray diffraction studies, scanning electron microscopy, transmission electron microscopy, and energy dispersive X‐ray spectra. Absorption spectra of CdS:Nd3+ and CdS:Pr3+ nanoparticles have been recorded at room temperature. Various parameters such as interplanar spacing, micro strain, dislocation density, distortion parameter, and particle size of nanomaterial are computed. TEM and XRD analysis reveal the spherical structure of the CdS:Nd3+ and CdS:Pr3+ nanoparticles in the prepared samples. Energy interaction parameters of the CdS:Nd3+ and CdS:Pr3+ nanoparticles are computed using UV‐visible absorption spectrum. Actually, CdS nanoparticle amplifies the luminescence intensity of Pr+3, Nd+3 ions by up conversion processes. So energy transfer can be observed from CdS nanoparticles doped with Pr+3, Nd+3 ions. Therefore, the use of pump sources and diode lasers in the UV range can be used to excite these samples to work as lasers. CdS:Nd3+ and CdS:Pr3+ nanoparticles find potential application as a window material for hetero‐junction solar cell, light emitting diodes (LED), biological sensors, address decoders, gas detectors, opto‐electronic devices, etc. CdS nanomaterials are also used as pigment in paints and in engineered plastic due to their good thermal stability.

Kerr-Lens Mode-Locked Yb:BaF2 Laser

We present sub-50 fs soliton pulse generation from a diode-pumped Kerr-lens mode-locked laser based on an Yb3+-doped BaF2 crystal. Utilizing a spatially single-mode, fiber-coupled InGaAs laser diode at 976 nm as a pump source, the Yb:BaF2 laser generates pulses as short as 46 fs at 1060.1 nm with an average output power of 45 mW at a pulse repetition rate of ~65.6 MHz via soft-aperture Kerr-lens mode locking. To the best of our knowledge, this represents the first demonstration of Kerr-lens mode-locked operation of the Yb:BaF2 crystal, as well as the shortest pulse duration ever achieved from any diode-pumped mode-locked laser based on an Yb3+-doped alkaline-earth fluoride crystal.

Design Considerations for Continuous Wave Intracavity Backwards Optical Parametric Oscillators

In this paper, we report a theoretical systematic study of continuous wave intracavity backwards optical parametric oscillators based on periodically poled lithium niobate (PPLN) for mid-infrared (mid-IR) light generation. We study the effects of varying different cavity parameters including nonlinear crystal length, cavity size, pump laser diode spot size, output coupler radius, and cavity loss values on the output power and threshold of the proposed mid-IR laser. The effects of different physical phenomena are included in the model including pump depletion due to the nonlinear conversion process, the thermal lens effect, and mode overlap between the beams in the nonlinear crystal. We show that high output powers in the mid infrared (>500 mW at 3.2 μm) can be achieved with proper cavity design and that a laser threshold with a PPLN as short as 2 cm can be reached.

All-solid-state ultrafast 2µm laser with 1.83 W output power.

In this paper, a high-power all-solid-state ultrafast 2µm mode-locked laser is investigated. The particularity of this laser is the simultaneous utilization of two Tm:YAP crystals in the same resonant cavity, independently pumped by two laser diodes. Using a 20% output coupler, pulses with output power as high as 1.83W are achieved at a wavelength of 1938nm with a pulse duration of 1.97ps and a pulse repetition frequency of 100MHz. To our knowledge, this mode-locked laser achieves the highest output power of any mode-locked Tm:YAP ultrafast laser reported to date. In addition, this paper provides a new approach to solve the problem of low output power due to multi-mode low-brightness laser diode pumping.