Diode-pumped Laser Research Articles

Intense broadband 3.1 μm emission in Er3+-doped fluoroaluminate-tellurite glass for mid-infrared laser application

Er3+ single doped fluoroaluminate-tellurite glasses were made by employing a conventional melt-quenching technique. A strong fluorescence around 3.1 μm was achieved from Er3+-doped fluoride glasses, under a 980 nm laser diode pump, which was assigned to the Er3+: 4S3/2 → 4F9/2 radiation transition process. The up-conversion and mid-infrared spectra of emission for fluoroaluminate-tellurite glasses with various concentrations of Er3+ ions dopant was researched. In addition, the calculated fluorescence lifetime value about 3.1 μm reaches 0.48 ms. The findings indicate that fluoroaluminate-tellurite glasses doped with Er3+ have prospects of being developed into 3.1 μm mid-infrared fiber and laser materials.

High-energy and high-beam-quality passively Q-switched Yb:KYW laser with extracavity frequency doubling

Yb3 + : KY ( WO4)2 (Yb:KYW) possesses various excellent properties, such as its highly polarized emission cross section, that makes it an excellent option for developing highly efficient diode-pumped solid-state lasers. A high-energy, high-beam-quality passively Q-switched Yb:KYW laser was demonstrated. The small-signal gain characteristics of the Yb:KYW crystal under quasi-continuous-wave laser diode (LD) pumping were obtained by theoretical analysis. Under LD end-pumping at a repetition rate of 500 Hz and a pumping width of 200 μs, the Q-switched Yb : KYW / Cr4 + : YAG laser operated at a wavelength of 1025 nm, and a single-pulse energy of 0.5 mJ was obtained with a pulse width of 5.8 ns. Near-diffraction-limited beam quality with an M2 value of ∼1.02 was achieved. The compact setup provided efficient second-harmonic generation at 512.5 nm via type-I phase matching using a LiB3O5 (LBO) crystal, and the output single-pulse energy was 0.13 mJ. We believe that these results further demonstrate the utility of Yb:KYW as a passively Q-switched laser crystal for solid-state lasers, particularly for applications that require nonlinear frequency conversion.

Demonstration of a diode-pumped plasma jet-type rare gas laser.

The diode-pumped metastable rare gas laser (DPRGL) is showing potential for high-power operation. A key issue in developing this concept is to produce high-density metastables in a large volume. To achieve this goal, we propose a new, to the best of our knowledge, architecture by extracting laser power from a diode-pumped plasma jet. In this scheme, the discharge and gain regions are separated, avoiding the negative effects of discharges in confined regions. A diode-pumped plasma jet-type Ar laser is demonstrated with 466-mW output and 33% slope efficiency. The gain volume can be increased with multi-jets, providing a better scaling potential for the DPRGL system.

An Efficiency Improvement Driver for Master Oscillator Power Amplifier Pulsed Laser Systems

The master oscillator power amplifier (MOPA) pulsed laser, one of the popular topologies for high-power fiber laser systems, is widely applied in industrial machining laser systems. In MOPA, the low-power pulsed laser, stimulated from a seed laser diode, is amplified by the high- power optical energy from pump laser diodes via the gain fiber. Generally, the high-power pump laser diodes are driven by lossy linear current drivers. The switched mode current drivers boost the driver efficiency but suffer from pulse energy consistency due to the current switching ripple. In this paper, a laser driver system that varies the switching frequency of current source to synchronize with pulsed laser repetition rate is analyzed and implemented. Experimental results are demonstrated using a 20 W pulsed fiber laser system.

High peak power, high repetition rate electro-optically Q-switched Nd:GdTaO4 1066 nm laser

In this work, we reported an electro-optically Q-switched Nd:GdTaO4 1066 nm laser under 879 nm laser diode pumping. Pulsed laser output at 1066 nm with a pulse width of 5.7 ns, a single pulse energy of 352 μJ and a peak power of 61.75 kW was obtained at 1 kHz when the pump pulse energy was 4.5 mJ. At a repetition rate of 2 kHz, the 45.4 kW peak power was achieved with a pulse width of 6.2 ns and a single pulse energy of 281 μJ. The optical-to-optical conversion efficiency was 8.1%. The beam quality factors of 2 kHz 1066 nm laser were measured to be M2x = 1.29, M2y = 1.21 at a pump pulse energy of 3.3 mJ by using the traveling 90/10 knife-edge method.

Triple-Wavelength Lasing with a Stabilized β-LaBSiO5:Nd3+ Crystal.

Multi-wavelength lasers, especially the triple-wavelength laser around 1060 nm, could be produced by the 4F3/2 → 4I11/2 transition of Nd3+ and present numerous challenges and opportunities in the field of optoelectronics. The Nd3+-doped high-temperature phase of LaBSiO5 (β-LBSO) is an ideal crystal to produce triple-wavelength lasers; however, the crystal growth is challenging because of the phase transition from β-LBSO to low-temperature phase (α-LBSO) at 162 °C. This phase transition is successfully suppressed when the doping content of Nd3+ is larger than 6.3 at. %, and the Nd3+-doped β-LBSO is stable at room temperature. The local disorder of BO4 tetrahedra due to Nd3+ doping is essential to the stabilization of β-LBSO. For the first time, the β-LBSO:8%Nd3+ crystal with a dimension of 1.8 × 1.8 × 1.8 cm3 is obtained through the top-seeded solution method. The crystal shows strong optical absorption in the range of 785-815 nm, matching well with the commercial laser diode pumping source. The optical emission of 4F3/2 → 4I11/2 splits into four peaks with the highest optical emission cross section of 2.14 × 10-20 cm2 at 1068 nm. The continuous-wave triple-wavelength generation of coherent light at 1047, 1071, and 1092 nm is achieved with the highest output power of 235 mW and efficiency of 12.1%.

High-power narrow-linewidth 780 nm diode laser based on external cavity feedback technology of volume Bragg grating

A diode-pumped alkali metal vapor laser (DPAL) combines the advantages of a solid laser and a gas laser. DPAL is useful in the industrial, medical, aerospace and military fields and can yield high output power while maintaining excellent beam quality. However, applications in many fields are limited due to the narrow absorption spectrum of the alkali metal vapor laser. In this study, a novel linewidth narrowing structure of the high-power diode laser based on volume Bragg gratings (VBGs) is proposed to match the absorption spectrum of the alkali metal vapor laser. With the combination of fast-axis collimating lens, beam transformation systems, slow-axis collimating lens, VBGs and metal ceramic heaters, the divergence angles of both fast and slow axis are compressed within 10 mrad. A high-power narrow linewidth diode laser source with a central wavelength of 780.044 nm, a spectral width of 0.138 nm, and an output power of 1090 W is achieved at an operating current of 50 A. Experimental results show that the effect of external cavity feedback based on VBG is improved and the multi-channel spectral linewidth is narrowed effectively by such a structure. The diode laser source based on this structure can be applied for pumping the rubidium alkali metal vapor laser.

Experimental investigation into fibre laser marking on stainless steel 304

ABSTRACT The operation of laser marking occurs due to oxidation on the metallic surface at a high temperature, which finds applications in many organisations due to its cleanness and high handling speed with the negligible human association. The generated marked objects are permanent in nature, generally utilised for product identity. From the perspective of laser marking, the general requirement of laser marking is mark clarity or marking quality with minimal effect on the workpiece surface. The paper deals with producing good-quality laser-marked surface by the utilisation of process parameters such as transverse feed, average laser power and scanning speed, which seem to have a significant effect on the surface of designed materials for the development of laser marking qualities. The diode-pumped pulsed fibre laser was utilised for the purpose of marking on the surface in a single pass within the minimum possible time. Experimental studies revealed that decrease in transverse feed from 8 μm to 2 μm/laser stroke had a projection towards the increase in mark intensity which could be reached up to 0.95 on the application of the lower value of transverse feed, i.e., 2 μm/laser stroke upon using a proper set of process parameters. .

Intense 2.9 µm mid-infrared emission from Dy3+/Yb3+：SrF2 crystal under 975 nm excitation

The intense 2.9 µm MIR (mid-infrared) luminescence corresponding to the Dy 3+ : 6 H 13/2 → 6 H 15/2 transition was achieved for the first time in Dy 3+ /Yb 3+ ions co-doped SrF 2 crystals. 2 at% Dy 3+ : SrF 2 ，2 at% Dy 3+ /5 at% Yb 3+ : SrF 2 , and 5 at% Yb 3+ : SrF 2 crystals were grown by Bridgman method. The influence of Yb 3+ on its spectral properties and energy transfer mechanisms has been studied. In comparison to Dy 3+ doped SrF 2 crystals, Dy 3+ /Yb 3+ co-doped crystals exhibit not only intense 2.9 µm emission but also longer high laser energy level lifetimes, favoring 2.9 µm population inversion and lasing behavior. Furthermore, the ET efficiency from Yb 3+ to Dy 3+ in Dy 3+ /Yb 3+ co-doped crystals is found to be as high as 95.34%, indicating that the ET from Yb 3+ is efficient. The results show that incorporating Yb 3+ into Dy 3+ : SrF 2 crystals improves the ability to achieve 2.9 µm lasing action, which could be used as a potential gain media for laser diode-pumped MIR lasers. • The Dy 3+ , Dy 3+ /Yb 3+ and Yb 3+ doped SrF 2 single crystals were grown by the Bridgman-Stockbarger method. • Intense 2.9 µm mid-infrared emission is observed in Dy 3+ /Yb 3+ : SrF 2 crystal under 975 nm excitation. • Detailed spectroscopic properties and energy transfer mechanisms were studied. • Dy 3+ / Yb 3+ : SrF 2 crystals are expected to achieve mid-infrared laser output.

Novel pumping scheme of Holmium doped fiber amplifiers operating around [formula omitted] using [formula omitted] lasers exploiting cascaded fiber lasers

The optical communication window around 2μm is attracting significant research attention for future optical communication systems as an extension to the C-, L-, and U-bands. One of the research topics in the 2μm region is optical amplifiers. Holmium-doped fiber amplifier (HDFA) is a suitable candidate for amplifying signals in this region. However, the pump laser for Holmium-doped fiber (HDF) is expensive and not widely available. In this work, we propose through numerical simulations, a novel pumping scheme to pump the HDF using commercially available 1.48μm lasers by exploiting cascaded fiber lasers made up of Erbium-doped fiber (EDF) and Thulium-doped fiber (TDF). The first fiber uses a commercially available 1.48μm laser to pump a piece of EDF to generate a 1.62μm continuous wave (CW) laser. This 1.62μm CW laser is used to pump a piece of TDF in the second fiber laser to create a 1.95μm CW laser that is used to pump the HDF. The HDFA can be used to amplify modulated optical signals in the 2μm wavelength range. A small-signal gain of 52.5 dB, 46.2 dB, and 32.6 dB can be achieved for input signal powers of −30 dBm, −15 dBm, and 0 dBm, respectively, at 2.032μm using a 5 W laser diode pump at 1.48μm. A noise figure (NF) of 7.5 dB, 6.6 dB, and 5.58 dB has been observed for input signal power of −30 dBm, −15 dBm, and 0 dBm, respectively at 2.032μm.

Two-level gas laser with transverse diode pumping

We theoretically study a new method for generating laser radiation by a two-level system without population inversion in the ‘red’ wing of its spectral line under resonant absorption of broadband radiation from pump laser diodes. A two-level system simulates the atoms of an active gas in an atmosphere of a high-pressure buffer gas. The effect results from the fact that in the ‘red’ wing of the spectral line, the probability of stimulated emission exceeds the probability of absorption if the homogeneous broadening due to the interaction of particles with the buffer gas significantly exceeds the natural one (at high pressures of the buffer gas). Analytical formulae are obtained that describe the operation of a two-level gas laser with transverse diode pumping. It is found that the longer the active medium, the higher the buffer gas pressure and pump radiation intensity, and the smaller the width of the pump radiation spectrum, the greater the efficiency of conversion of pump radiation into laser radiation. In a sufficiently long active medium (the length of the medium is 50 times its width), the conversion efficiency can reach 44 % at a buffer gas pressure of 5 atm, a pump diode radiation intensity of 3 kW cm−2, and a half-width of its spectrum of 1 cm−1. A two-level gas laser with transverse diode pumping is capable of generating continuous optical radiation with a very high (up to 100 kW) power. The frequency of laser radiation can be tuned by several tens of cm−1.

Specific features of radiation flux formation in diode-pumped lasers and amplifiers with active elements made of Nd : YAG ceramics

The spatial, temporal, and spectral characteristics of the output radiation of diode-pumped laser systems and optical amplifiers with active elements made of Nd : YAG ceramics are studied. It is shown that the divergence of radiation in the subthreshold regime has the form of concentric nested cones emerging from the active element (AE) faces at angles of 2 – 4 °. A model explaining the experimentally observed phenomenon is proposed based on the mechanism of scattering of the generated beam from the granular structure of the optical ceramics. Analysis of the divergence pattern makes it possible to estimate the grain size and the optical quality of ceramics. The output beam divergence in the lasing regime is determined mainly by the cavity parameters and does not exceed several milliradians. The scattering events in this case serve as sources of additional optical losses. Luminescence enhancement and parasitic oscillations in the AE volume restrict the possibility of using Nd : YAG ceramics for fabricating AEs of high-power optical amplifiers.

Assessment of optical and fluorescence aspects of Er3+-doped multicomponent B2O3 glasses as active media for 1.532 μm near-infrared optical amplifiers

Current work principally provides an idea on controlling the Er3+: NIR (near-infrared) emission characteristics by changing a glass constituent and finding a suitable glass host favorable to design a novel C-optical band (1.53–1.565 μm) amplifier. By melting and rapid quench route, six transparent Er3+ (1 mol%)-doped B2O3-rich glasses having different single and mixed alkali ions were fabricated, and optical and fluorescence (visible and NIR) traits including Er3+ ion upper-levels 4S3/2 and 4I13/2 decay dynamics were inspected for such samples. At 1.4–1.65 μm wavelength range, an intense and wide NIR luminescence band centered at 1.532 μm (Er3+: 4I13/2 → 4I15/2 transition) has been obtained by a 980 nm laser diode pumping (4I15/2 → 4I11/2). NIR fluorescence Δλeff (effective bandwidth) varied depending on added single or mixed alkali ions, and a maximum Δλeff ∼74.66 nm was acquired for Er3+: Li ions constituting glass. For the 4I13/2 → 4I15/2 transition, σemi (stimulated emission cross-section) was evaluated using both Füchtbauer–Ladenburg and McCumber's theories. In all glasses, comparably, higher gain bandwidth (= 5.384 × 10−26 cm3) and peak σemiM (= 1.692 × 10−20 cm2) values have been attained for 4I13/2 → 4I15/2 transition in Li ions containing sample, and also this glass possesses the largest σabs (absorption cross-section) (= 1.459 × 10−20 cm2) for 4I15/2 → 4I13/2 transition. Further, at distinctive P (population inversion) values, gain spectra were computed, and all samples show C-optical band amplification beginning from P = 50%. All analyzed NIR fluorescence results indicate that Li ions having glass could be a potential gain medium for fiber amplifiers.

Compact Passively Q-Switched Tm:KY(WO<sub>4</sub>)<sub>2</sub> Laser

Diode-pumped thulium lasers emitting in the spectral range near 2 μm are attractive for applications in different areas: surgery, rangefinding, and environmental atmosphere monitoring. In this article the latest results of Tm:KYW laser performance with a polycrystalline Cr:ZnSe as the most available saturable absorber for 2 μm spectral region are presented.A maximum continuous-wave output power of ≈ 0.65 W with a slope efficiency of 55 % was obtained at the wavelength of 1940 nm. Laser pulses with energy of 26 μJ and repetiotion rate of 6 kHz coresponding to 156 mW of average output power at 1910 nm were obtained at 2.2 W of incident puwp power for the Cr:ZnSe saturable absorber with initial transmission of 95 %. By using of saturable absorber with lower initial transmission of 90 % laser pulses with energy of 40 μJ and duration as short as 10 ns were realized. The maximal pulse repetition rate was 2.8 kHz at incident pump power of 2.2 W.Based on the obtained results, it can be concluded that Tm:KYW crystals are promising active media for the compact passively Q-switched lasers emitting in the spectral range near 2 μm for the usage in surgery and rangefinding. Also, described laser is planned to be used as a laser source in laser-induced damage threshold measurements setup for investigation of damage threshold of saturable absorbers as well as nonlinear crystals at the wavelength near 2 μm.

High-Power Dual-Wavelength Laser Based on Coaxial End-Pumping Scheme With Combination of Gain Media

A high-power dual-wavelength laser based on coaxial end-pumping scheme with composite Nd:YAG and Nd:YAP crystals was demonstrated. A theoretical model was built to analyze the thermal lens and accurately calculate the thermal focal length of laser gain medium pumped by a divergent beam. The experiment was carried out with a plane-convex cavity and a V-shape cavity for high-power output. The Q-switched laser produced 9.1 W pulsed dual-wavelength output (4.7 W at 1064 nm and 4.4 W at 1079 nm) at 25-kHz pulse repetition rate with synchronized pulse duration of 35 ns, corresponding to the optical-to-optical efficiency of 30.3%. The continuous-wave (CW) output power reached 15.5 W at laser diode (LD) pump power of 40 W, corresponding to a slope efficiency of 40.9% and an optical-to-optical conversion efficiency of 38.9%. The powers at two wavelengths were almost equivalent and the fluctuations were both less than 2.3%. To our best knowledge, it was the highest output power for stable CW dual-wavelength lasers based on diode-end-pumped configuration.

Red-diode-clad-pumped CW and mode-locked Er:ZBLAN fiber laser at 3.5 µm.

We report on a red-diode-clad-pumped continuous-wave (CW) and mode-locked Er:ZBLAN fiber laser at 3.5 µm for the first time. Numerical simulation shows that a heavily-doped Er:ZBLAN fiber is favorable for effective generation of 3.5 µm laser through 658 nm laser diode pumping. Using a 7.0 mol.% Er:ZBLAN fiber, CW output power of 203 mW was experimentally obtained at 3462 nm. By incorporating a home-made semiconductor saturable absorber mirror into the cavity, diode-pumped CW mode-locked 3.5 µm Er:ZBLAN fiber laser was first demonstrated with an average power of 19 mW, a pulse duration of 18.1 ps, and a repetition rate of 46 MHz. The research results show that red-diode-clad-pumping provides a simple and potential scheme for 3.5 µm CW and mode-locked Er:ZBLAN fiber laser.

Diode-pumped Dy:KPb2Cl5 laser in the middle-infrared spectral region.

A Dy:KPb2Cl5 (KPC) laser oscillating at approximately 4.4 µm under diode laser pumping at 1.7 µm is demonstrated for the first time. A maximum output pulse energy of 1.1 mJ was achieved at 10 mJ of absorbed pump energy. Tunable laser oscillation in the 4.2-4.5 µm spectral range was recorded with this crystal. Limitations of Dy:KPC for laser oscillation due to its challenging thermo-optical properties are discussed. This crystal is a further addition to the range of low-phonon-energy materials doped with Dy ions that can be applied for laser oscillation in the mid-infrared spectral range under direct diode laser pumping.

High repetition rate diode-pumped self-pulsed few-cycle alexandrite laser

We reported a high repetition rate diode-pumped alexandrite femtosecond laser using a simple linear cavity. Laser emission spectrum was as broad as ∼20 nm by inserting a 0.5-mm-thick quartz birefringent plate as a spectral modulation component. Pulse duration as short as few-cycle 36 fs with the repetition rates of 2.48 GHz was measured at pump power of 17 W. To the best of our knowledge, this is the shortest pulse duration achieved in the alexandrite lasers.

Optical Amplifiers for Multi–Band Optical Transmission Systems

Opening new wavelength bands is the most economic step for further increasing the capacity of optical transmission links. Characteristics of different amplifier technologies for signal amplification in different wavelength bands are detailed. In particular, the suitability of these technologies for short–term and mid–term implementation is considered. An important criterion is the availability of qualified components, notably the required pump laser diodes. On this basis, solutions for the near–term and the mid–term are discussed.

A diode-pumped femtosecond Pr:YLF laser emitting at the near-infrared 915 nm

Femtosecond pulse generation from diode-pumped praseodymium (Pr) lasers in the near-infrared has been a long pursuit for the optics community. Utilizing the Pr:LiYF4 crystal in a novel dispersion arrangement scheme that includes a set of triple Gires-Tournois interferometer mirrors, mode-locked ultrashort pulses as short as 451 fs at 915 nm have been achieved when the crystal is directly pumped by a blue laser-diode. The pulse energy is 3 nJ and peak power is 7.2 kW at the repetition rate of 85.5 MHz. This is the first demonstration of diode-pumped Pr lasers arriving the femtosecond regime.