LD Pumping Research Articles

Growth and spectroscopic properties of Dy3+:GdCa4O(BO3)3 crystals

8 at.%, 10 at.%, and 12 at.% Dy3+ ions doped GdCa4O(BO3)3 crystals were successfully grown by the Czochralski method. The Raman spectrum showed that the maximum phonon energy was 937 cm−1. Detailed investigation of polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curve of the Dy3+:GCOB crystals showed that all the three crystals had good spectral properties. The strong and wide absorption peaks at 454 nm indicated that the crystals were fit for commercially available blue InGaN LD pumping. The intense and broad emission bands at around 585 nm, and long fluorescence lifetimes, revealed that the Dy3+:GCOB crystals were potential solid-state laser materials for yellow laser.

Structure and Spectral Properties of Er3+-Doped Bismuth Telluride Near-Infrared Laser Glasses.

TeO2-Bi2O3-B2O3-ZnO laser glasses doped with Er3+ were synthesized through an optimized melt-quenching method. The absorption spectra at 808 nm LD pumping were studied. Various spectral tests and data analyses indicate that the maximum fluorescence emission intensity can be obtained when the Er3+ doping concentration reaches 2%. In this case, the emission cross-section can reach up to 9.12 × 10-21 cm2 and the gain coefficient at 1.55 μm is 6.17 cm-1. Simultaneously, the sample has a lower phonon energy in the high-frequency band at 1077 cm-1, which reduces the probability of non-radiative relaxation. The calculated energy transfer coefficient CD-A is 13.8 × 10-40 cm6/s, reflecting the high cross-relaxation probability of Er3+ in the sample, which promotes the luminescence of 1.55 μm and favors the emission in the near-infrared region. The comprehensive results demonstrate that the prepared Er3+-doped bismuth telluride laser glass can be used as a promising and high-quality gain material for near-infrared lasers.

A simple approach to start Mamyshev oscillator at 1030 nm utilizing a saturable absorber mirror

We demonstrate a simple method to start Yb fiber Mamyshev oscillator by adding a saturable absorber mirror (SAM) in an optical path at a bandpass filter reflection. At first, to achieve the starting of Mamyshev oscillator using SAM, by injecting a seed pulse from outside the cavity, an output coupling, a transmitted central wavelength between offset bandpass filters, and a pump LD power are explored to start the Mamyshev oscillator. Then, preserving the above-mentioned three parameters in the cavity, we exchange a fiber-cabled mounted SAM for the seed pulse output FC/APC connector. After that, the Mamyshev oscillator immediately started by turning on the pump LD. To understand the starting dynamics of this approach, we capture the pulse resolved spectrum in an initial stage of the pulse formation of Mamyshev oscillator by time-stretch spectroscopy. Before starting Mamyshev oscillator, a signature of the Q-switch pulse is observed in the 2D color plot imaging of the pulse-resolved single-shot spectrum. When a strong amplified spontaneous emission is input to SAM, a Q-switch pulse is created, and then this Q-switch pulse circulates in the cavity. This Q-switching pulse plays a role in the seed pulse to start the Mamyshev oscillating. We believe this simple approach is one of the efficient techniques for starting the Mamyshev oscillator.

Sub-Nanosecond, High Peak Power Yb:YAG/Cr4+:YAG/YVO4 Passively Q-Switched Raman Microchip Laser with the Emission of Multiple Pulses

This paper demonstrates the capability of sub-nanosecond, high peak power Yb:YAG/Cr4+:YAG/YVO4 passively Q-switched Raman microchip lasers at 1134 nm operated in multiple pulses mode under quasi-continuous-wave (QCW) pumping. Total pulse energy for the Stokes laser was 1.8 mJ with a 4 mm YVO4 crystal and TOC = 16%. The corresponding pulse repetition rate reached 225 kHz within a single pumping pulse. By employing a compact plane-concave cavity and 5 mm YVO4 crystal, the single pulse energy for the Raman laser was further scaled up to 44 μJ. The corresponding peak power was 95 kW. A highest output pulse repetition rate of 87.8 kHz and shortest pulse duration of 464 ps were found for the Raman laser. The results indicate that the Raman microchip laser configuration under QCW LD pumping is a promising approach for developing high peak power, commercial and portable Raman lasers with a pulse duration of several hundred-picoseconds at a pulse repetition rate of hundred kilohertz.

Direct Kerr-lens mode-locked Tm: LuYO3 ceramics laser

Abstract A direct Kerr-lens mode-locked Tm: LuYO3 ceramics laser without the aid of any mode-locked starting element is reported for the first time. The pulse duration as short as 259 fs and maximum average output power of 326 mW are obtained at a repetition rate of 97.1 MHz. The corresponding optical spectrum centered at 2053 nm exhibits a bandwidth of 19.8 nm, which indicates the presence of nearly Fourier transform-limited pulses. Such a Kerr-lens mode-locked Tm: LuYO3 ceramics laser is a promising ultrashort pulse source, with both the excellent laser characteristics of Tm: LuYO3 and the high-power 790 nm LD pumping scheme.

High energy multi-mode nanosecond pulsed fiber amplifier based on the 940 nm LD pumping with effective suppression of the ASE and the SRS effect

We demonstrated, for the first time, an amplified spontaneous emission (ASE) and stimulated Raman scattering (SRS) free multi-mode nanosecond pulsed fiber amplifier based on the 940 nm LD pumping. The maximum pulse energy reached 15.3 mJ at the average output power of 306 W using a 100/400 Yb-doped extremely large mode area fiber. A near top-hat beam with M2 = 10.4 was achieved. This is the highest pulse energy generated from the 940 nm LD pumped multi-mode nanosecond pulsed fiber amplifier. In addition, comparative experiments based on the conventional 915 nm LD pumping and the 976 nm LD pumping were conducted. The results showed that the 915 nm LD pumping lead to intensive forward 1030 nm ASE, and the 976 nm LD pumping was limited by strong backward ASE power. These confirmed that the 940 nm LD pumping provided an effective method to suppress the ASE and the SRS effect in the high energy multi-mode nanosecond pulsed fiber amplifier.

All-fiber Mid-infrared enhanced supercontinuum generation in an Erbium-doped ZBLAN fiber amplifier

We demonstrated all-fiber mid-infrared enhanced supercontinuum generation in an Erbium-doped ZBLAN fiber amplifier. A 2 μm low repetition rate noise like-pulse mode-locked fiber laser was adopted as the pulse seed for the system. After amplified in a Thulium-doped fiber amplifier, the noise like-pulse generated a supercontinuum covering the range from ∼2 μm to ∼3.8 μm in a piece of InF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> fiber. Then, the supercontinuum was injected into an Erbium-doped ZBLAN fiber amplifier as the seed for the next stage in-amplifier mid-infrared enhanced supercontinuum generation. A novel silica-fluoride fiber pump combiner was designed and fabricated to couple the 976 nm LD pump laser into the Erbium-doped ZBLAN fiber. The supercontinuum laser source realized mid-infrared enhancement and power boosting beyond 2.7 μm in the Erbium-doped ZBLAN fiber amplifier. A ∼1.4 W mid-infrared enhanced SC with long wavelength edge of ∼4200 nm and 97% power beyond 2.7 μm was obtained. This simple and compact all-fiber supercontinuum laser source has a great potential application in the 3-5 μm molecular fingerprint region.

Enhance and modulated near-infrared luminescence of Tm3+:CaF2 crystal by co-doping Y3+ ions

A series of 0.5 at.% Tm:Ca1-xYxF2+x (x = 0, 0.01, 0.04, 0.06, 0.08, 0.12) crystals have been successfully grown by the temperature gradient technique (TGT) method. The absorption spectra, fluorescence spectra, and fluorescence decay curves were measured and analyzed at room temperature. By comparison, it is found that when the concentration of Y3+ ions reaches 8 at.%, the absorption cross section corresponding to the 3H6→3H4 energy level is 2.56 × 10−21 cm2 at 793 nm, which is suitable for GaAlAs LD pumping. The J-O strength parameters Ω2, Ω4, and Ω6 were obtained. With the incorporation of Y3+ ions, the value of Ω4/Ω6 gradually increases. When the concentration of Y3+ ions reaches 8 at.%, the emission cross sections are 3.05 × 10−21 cm2 at 1476 nm, 2.56 × 10−21 cm2 at 2378 nm, and the full widths at half maximum (FWHM) are 76 nm and 195 nm, respectively. The fluorescence lifetime of 3H4 level, the upper level of 1.5 μm and 2.3 μm, is 1.05 ms, which is very beneficial for 1.5 μm and 2.3 μm laser.

High efficiency and high beam quality Er:YSGG Mid-infrared continuous-wave laser

We demonstrated an LD end-pumped Er:YSGG mid-infrared (MIR) continuous-wave (CW) laser based on optimized LD pump wavelength with less absorption coefficient and thermal problems. A composite crystal YSGG/Er:YSGG/YSGG with a size of 3 × 3 × 14 (2 + 10 + 2) mm3 was employed, and its central part had an erbium ion doping concentration of 38 %. The maximum output power of 2.8 μm MIR laser is 2.01 W, corresponding to a slope efficiency of 28.89 %, at which the beam quality M2 of the laser is 1.19. Compared with other Er3+-doped laser, we achieved a CW MIR laser with higher efficiency and better beam quality. The results suggest that optimizing the wavelength of the pump source and adopting the crystal bonding technology could effectively improve the performance of the LD end-pumped Er:YSGG CW MIR laser.

Thermal modeling of resonantly pumped high power Tm-doped fiber amplifiers

A thermal model concerning resonantly pumped high power Tm-doped fiber amplifiers is established with temperature dependent parameters taken into consideration. With this model, performance of resonantly pumped Tm-doped fiber amplifiers at 1 kW output is investigated. Comparisons with the traditional 793 nm LD pump scheme shows that, resonant pumping, especially the 1.9 μm pump, is more favorable for high power Tm-doped fiber systems, featuring high operation efficiency with low heat load, limited temperature rise, controllable beam compression and a relatively small laser intensity at the output end. Besides, the power scalability of resonantly pumped Tm-doped fiber systems with 25/250 double-clad fiber is also explored numerically with various thermal effects, optical damage and nonlinear effects taken in account. Simulations show that, for 1 GHz narrow linewidth output, outer cladding damage and stimulated Brillouin scattering are the two primary limiting factors for power scaling. And, the maximal output of a Tm-doped fiber amplifier could reach 5.1 kW and 6.8 kW for 1.6 μm pump and 1.9 μm pump, respectively. For systems with broad spectrum, output approaching 10 kW can be expected.

Pulsed Raman fiber lasers based on multimode graded-index fiber with LD pumping

Pulsed Raman fiber lasers based on multimode graded-index fiber with LD pumping

Growth and spectroscopic analyses of Yb,Ho:CaYAlO4 disordered crystal for ~3 μm mid-infrared laser

Ho:CaYAlO4 (Ho:CYA) and Yb,Ho:CaYAlO4 (Yb,Ho:CYA) disordered crystals exhibiting high optical nature were successfully grown by the Czochralski method for ~3 μm mid-infrared laser. The polarized absorption spectra and J-O parameters were analyzed. A strong 2.86 μm emission with the FWHM of 111 nm had been realized in Yb,Ho:CYA crystal via Yb3+ ions sensitization, corresponding to the emission cross-section of 1.4 × 10−20 cm2. The comparable emission peak at 1.2 μm and fluorescence lifetime of Ho3+:5I6 level indicated an effectively energy transfer from Yb3+:2F5/2 to Ho3+:5I6. The efficiency was calculated to be about 83.5%. All above results suggest that Yb,Ho:CYA crystal is a potential laser host for ~3 μm mid-infrared ultrafast and tunable laser under the commercial 980 nm LD pump.

Experimental and theoretical analysis on pump spectral propriety of single frequency Erbium-Ytterbium co-doped fiber amplifier

The pump spectral propriety of three types of commercial 915 and 976 nm LDs on single frequency Erbium-Ytterbium co-doped fiber amplifier (EYDFA) is theoretical and experimental analyzed. The slope efficiency, ASE intensity and linewidth broadening of the wavelength stabilized or un-stabilized LDs pumped amplifier are compared in detail. The results demonstrate that 976 nm LD pumping exhibits superior to 915 nm LD in efficiency and SNR. Comparing with wavelength stabilized 976 nm LD, the wavelength un-stabilized 976 nm LD with center wavelength deviating from Yb absorption peak and over 4 nm linewidth has better performance in Yb-ASE suppression but slightly lower in efficiency and linewidth broadening. The difference between the two 976 nm LDs could be taped off by increasing the seed power or output power. This work indicate that wavelength un-stabilized 976 nm LD is more suitable for pumping high power single-frequency EYDFA to avoid the bottlenecking effect, and provide reference for the optimal pump selection.

Thermal, and optical features study of Dy:YAlO3 and Dy/Tb:YAlO3 crystals for yellow laser applications

Optical features of Dy3+:YAP and Dy3+/Tb3+:YAP single crystals that were successfully fabricated by the Czochralski method were reported. The thermal behaviors and XRD rocking curves of the grown Dy3+:YAP crystal were carried out. The identified broad absorption bands of Dy3+:6H15/2 → 4I15/2 with FWHMs approximately to 11 nm and the moderate absorption cross-sections at 450 nm in both crystals, imply their high suitability to the blue LD pumping. Polarized emission spectra with yellow fluorescence peaks at 572 nm were acquired in both crystals by means of a 450 nm Xenon lamp excitation. As compared with Dy3+:YAP crystal, the larger emission cross-sections of 7.83 × 10−21, 9.08 × 10−21 and 9.01 × 10−21 cm2 for E//a, E//b and E//c polarizations respectively, were determined in Dy3+/Tb3+:YAP crystal. Moreover, a slightly reduced lifetime of the upper laser level 4F9/2 and a much shortened lifetime of the lower laser level 6H13/2 were obtained in Dy3+/Tb3+:YAP crystal, implying the existent energy migration between Dy3+ and Tb3+, as well as an effective deactivation of Tb3+ to Dy3+. The role of Tb3+ to reinforce Dy3+:4F9/2 → 6H13/2 emission in YAP host was established. On the basis of the derived results, both crystals could be recognized as competitive materials for polarized yellow lasers, especially the Dy3+/Tb3+:YAP crystal.

J-O study of a novel Dy-doped Lu3Al5O12 transparent ceramic for potential application in yellow laser generation

A novel Dy:LuAG transparent ceramic was fabricated by a solid-state method, and it has the potential to be used as the gain medium of yellow laser generated by blue LD pumping. The spectroscopic parameters were determined by the Judd-Ofelt theory, and Ω2, Ω4, Ω6 were calculated to be 0.57 × 10−20 cm2, 1.44 × 10−20 cm2, 0.68 × 10−20 cm2, respectively. An intense yellow emission band, corresponding to the 4F9/2 → 6H13/2 transition located at 581 nm, was observed in the visible region. The non-exponential curve was fitted to the Inokuti–Hirayama model to understand the energy-transfer mechanism. The fluorescence lifetime of the 4F9/2 level was about 339 μs, and the quantum efficiency was 21.7%.

A potential ultrafast pulse laser crystal with disordered melilite structure: Yb3+: CaLaGa3O7

The Yb3+: CaLaGa3O7 crystal with high-quality was grown successfully by the Czochralski method. The structure parameters of Yb3+: CaLaGa3O7 crystal are determined by the X-ray Rietveld refinement method. The absorption and fluorescence spectra, fluorescence lifetime and laser performance parameters were investigated in detail. The large absorption cross-section (1.14 × 10−20 cm2 for π-polarization and 1.06 × 10−20 cm2 for σ-polarization) of the crystal at around 980 nm indicates that the crystal can be pumped efficiently by the commercialized InGaAs laser diode. The stimulated emission-cross section at 1004 nm was calculated to be 1.11 × 10−20 cm2 for π-polarization and 1.04 × 10−20 cm2 for σ-polarization. The above results reveal that Yb3+: CaLaGa3O7 crystal can be regarded as a potential candidate for realizing tunable solid-state and ultrashort pulsed lasers with LD pumping.

Cr-doped Ca3NbGa3Si2O14: A promising near-infrared tunable laser crystal

Broad tunable solid-state lasers in the near-infrared region are urgently demanded due to their critical applications in optical communications, eye-safe imaging, medicine and spectroscopy, and Cr4+-based lasers exhibit good application prospect in this area. Herein, we reported a new near-infrared tunable laser crystal of Cr-doped Ca3NbGa3Si2O14 (Cr:CNGS). By employing the Czochralski method, single crystal of Cr:CNGS with dimensions of Φ 20 × 30 mm3 was grown. Its crystal structure, spectral properties were investigated in detail., Cr:CNGS exhibits attractive properties, including broad emission band at 800–1400 nm, long fluorescence lifetime (18 μs at 298 K) and good adaptability to LD pumping source, all of these characteristics enable it to be a potential laser crystal for the near-infrared tunable lasers. Notably, we discovered that the multi-sites in CNGS crystal make Cr ions exist in different valence states simultaneously, including Cr3+, Cr4+ and Cr5+, which is also partly responsible for its broadband emission.

Judd-Ofelt analysis and spectroscopic study of Tb:CaF2 and Tb/Pr:CaF2 co-doped single crystals

Abstract High quality of Tb3+-single doped and Tb3+/Pr3+ co-doped CaF2 crystals were grown by the temperature gradient technique (TGT). Pr3+ ions were used as sensitizing ions of Tb3+. Optical properties including absorption spectrum, emission spectrum, and fluorescence decay curve were recorded. Through co-doping sensitizing ions of Pr3+, the absorption cross section around 480 nm increased from 0.007 × 10−20 cm2 to 0.3 × 10−20 cm2, the large value is beneficial for the absorption of LD pump source. Judd-Ofelt theory was used to analyze the spectroscopic parameters. Fluorescence branch ratio, transition probability, radiative and fluorescence lifetimes, and quantum efficiency were determined as well. The emission cross section of Tb,Pr:CaF2 for the green emission at 544 nm and yellow emission at 587 nm corresponding to the transition of 5D4→7F5 and 5D4→7F4 were calculated to be 5.56 × 10−22 cm2 and 8.78 × 10−23 cm2, respectively, which is comparable to the Tb3+ doped CaF2 crystal.

Growth and spectroscopic properties of Yb0.1Gd1.8La0·1SiO5 crystal: A promising new laser material for ultrashort laser

Recently, in the field of femtosecond lasers, an intense interest has been aroused for Yb3+-doped laser crystals which are able to be pumped directly by semiconductor laser. In this work, a novel Yb3+-doped mixed laser crystal Yb0.1Gd1.8La0·1SiO5 (Yb:GLSO) crystal with high-quality was grown successfully by Czochralski method. Raman spectrum confirmed that the Yb:GLSO has highly disordered crystal structure. The large absorption cross section (0.70 × 10−20 cm2) of Yb:GLSO crystal at around 975 nm indicates the crystal can be pumped efficiently by the commercialized InGaAs laser diode. The stimulated emission cross section at 1030 nm was calculated to be 0.7 × 10−20 cm2 and the bandwidth of the emission peak was determined as high as 175 nm. Positive gain cross sections were appeared at 1030, 1045 and 1088 nm when inversion ratio higher than 0.2. All these results suggest that Yb:GLSO crystal is a very promising novel laser material for realizing tunable solid-state and ultra-short pulsed lasers with LD pumping.

Progress of the research on Yb 3+ -doped femtosecond laser crystals

As widely used in military, medicine, communication, processing and other fields, femtosecond laser has become a research hotspot of the whole laser technology in the 21st century. The pump source used by laser diodes (LDS) has become a new development trend of all-solid-state femtosecond lasers owe to the rapid development of LDs. Yb3＋-doped laser crystal materials gradually become important gain media for LD pumping and generate 1.0 μm femtosecond laser due to their unique energy level structures, broad absorption and emission spectra. In this paper, the research progress of Yb3＋-doped femtosecond laser crystals is summarized in detail, the main problems are analyzed, and two directions for the development of femtosecond laser crystals in the future are proposed: high efficiency and low power femtosecond laser, high power and high energy femtosecond laser. The crystal growth, spectra properties, continuous and femtosecond laser performances of the Yb3＋:Sr3Y2(BO3)4 crystal were studied in detail. And the Yb3＋:Sr3Y2(BO3)4 femtosecond laser with the center wavelength of 1060 nm, pulse width of 116 fs, average output power of 1.08 W and optical conversion efficiency of 33.1% were successfully generated. The experimental results indicate that Yb3＋:Sr3Y2(BO3)4 and its corresponding system crystals are excellent femtosecond laser materials with high optical conversion efficiency.