Experimental investigation of the 2.1-μm single-mode Tm-Ho:KYF laser

We report on the development and comprehensive characterization of a room-temperature single-mode 2-m Tm-Ho:KYF laser. A maximum CW output power of 70 mW at the central wavelength of 2.078 m has been obtained. Using a 5-mm long intracavity birefringent filter the single-mode emission wavelength can be tuned over a range of 40 nm. Both frequency and relative intensity noise have been investigated showing a 1-ms emission linewidth of 600 kHz and an intensity noise spectrum that is quantum-noise limited for Fourier frequencies higher than 1 MHz. PACS 42.55Xi; 42.55Rz; 42.60Pk; 42.70Hj; 42.60Lh     

A 110-W fiber laser with homemade double-clad fiber

A high-power ytterbium-doped fiber laser (YDFL) with homemade double-clad fiber (DCF) is introduced in this letter. The geometric parameter and laser characteristics of the fiber have been studied. With oneend-pumping scheme, pumped by a high-power laser diode with launching power of 280 W, a maximum continuous wave (CW) output of 110 W is obtained with an optical-to-optical efficiency of 40%.     

AlGaInAs multiple-quantum-well 1.2-μm semiconductor laser in-well pumped by an Yb-doped pulsed fiber amplifier

An AlGaInAs multiple quantum well structure is reported as an effective gain medium of the in-well pumped high-peak-power semiconductor disk laser at 1.2 μm. We use an Yb-doped pulsed fiber amplifier as the pump source to effectively optimize the output characteristics. The maximum average output power of 1.28 W and peak output power of 0.76 kW is obtained at 1225 nm lasing wavelength under 60 kHz pump repetition rate and 28 ns pump pulse width.     

Self-swept erbium fiber laser around 1.56 μm

Self-swept erbium fiber laser emitting around 1.56?μm is reported in detail. Both sweep directions were registered: pointing toward longer and shorter wavelengths, redshift and blueshift sweeping, respectively. We describe method of determining the direction of the wavelength drift using the monochromator based optical spectrum analyzer. Possible root for this sweeping regime, i.e., the gain modulation along active fiber, is discussed with the help of a simple model calculating the overall cavity gain that can predict the direction of the laser wavelength sweeping.     

1.55-μm non-anti-reflection-coated fiber grating laser for single-longitudinal mode operation

A 1.55-m fiber grating laser (FGL) was fabricated by optically packaging a non-anti-reflection (AR) coated Fabry–Perot (FP) laser to a lensed fiber grating. The FGL demonstrates a single-longitudinal mode operation with a side-mode suppression ratio (SMSR) of up to 40 dB. The SMSR oscillates and diminishes to <30 dB as the increase of injection current above 38 mA, and the tilt of the fiber approaches 5° away from the facet normal of the FP laser. We have performed numerical simulations on the single-longitudinal mode operation for the FGL. The SMSR for the FGL increases over 40 dB as the increase of the fiber grating reflectivity (R _g) above 0.7 with non-AR-coated FP laser facet. Our calculations also show that the strong current-dependent SMSR oscillation is from the mode selection by the fiber grating external cavity and the heating effect in the FP laser.     

2-μm high-power multiple-frequency single-mode Q-switched Ho:YLF laser for DIAL application

We report on the development and the demonstration of a two-wavelength single-frequency laser oscillator based on Ho:YLF crystal. This laser is especially suitable for application as a transmitter in differential absorption lidar (DIAL)/integrated path differential absorption (IPDA) measurements of atmospheric carbon dioxide (CO₂) using the R30 CO₂ absorption line at 2,050.967 nm. The oscillator consists in a fiber-coupled and free-space solid-state hybrid system and can be used in high-energy middle-rate or moderate-energy high-rate configurations. The latter produced On and Off sequentially single-frequency laser pulses with 13 mJ of energy at a repetition rate of 2 kHz and pulse duration of 42 ns. The pulse energy and frequency stabilities are specially documented in free-running, single-frequency and two-frequency seeding single-mode operations. Standard deviation is 7.7 % for pulse energy and 2 MHz for frequency stability for the two-wavelength seeding operation. Allan variance plot shows that frequency fluctuations are reduced below 70 kHz for 10 s of averaging which is suitable for accurate CO₂ DIAL or IPDA measurements.     

Generation of 131 fs mode-locked pulses from 2.8μm Er:ZBLAN fiber laser

We demonstrated a femtosecond mode-locked Er:Zr F4-Ba F2-La F3-Al F3-Na F(Er:ZBLAN)fiber laser at 2.8μm based on the nonlinear polarization rotation technique.The laser generated an average output power of 317 m W with a repetition rate of 107 MHz and pulse duration as short as 131 fs.To the best of our knowledge,this is the shortest pulse generated directly from a mid-infrared mode-locked Er:ZBLAN fiber laser to date.Numerical simulation and experimental results confirm that reducing the gain fiber length is an effective way to shorten the mode-locked pulse duration in the Er:ZBLAN fiber laser.The work takes an important step towards sub-100-fs mid-infrared pulse generation from mode-locked Er:ZBLAN fiber lasers.     

2-μm mode-locked nanosecond fiber laser based on MoS_2 saturable absorber

We demonstrated a 2-μm passively mode-locked nanosecond fiber laser based on a MoS_2 saturable absorber(SA).Owing to the effect of nonlinear absorption in the MoS_2 SA, the pulse width decreased from 64.7 to 13.8 ns with increasing pump power from 1.10 to 1.45 W. The use of a narrow-bandwidth fiber Bragg grating resulted in a central wavelength and 3-dB spectral bandwidth of 2010.16 and 0.15 nm, respectively. Experimental results show that MoS_2 is a promising material for a 2-μm mode-locked fiber laser.     

Sb_2Te_3 mode-locked ultrafast fiber laser at 1.93μm

Ultrafast pulse generation was demonstrated in thulium doped fiber laser mode locked by magnetron sputtering deposited Sb_2Te_3with the modulation depth,non-saturable loss,and saturable intensity of 38%,31.2%,and 3.3 MW/cm~2,respectively.Stable soliton pulses emitting at 1930.07 nm were obtained with pulse duration of 1.24 ps,a 3-dB spectral bandwidth of 3.87 nm,an average output power of 130 m W,and signal-to-noise ratio(SNR)of 84 dB.To our knowledge,this is the first demonstration of Sb_2Te_3-based SA in fiber lasers at 2-μm regime.     

Graphene-based passively Q-switched 2 μm thulium-doped fiber laser

We demonstrated stable pulses generation at 2 μm in a passively Q-switched thulium-doped fiber laser using a few layer graphene thin film. The maximum output power was 4.5 mW and the single pulse energy was 85 nJ at 53 kHz repetition rate, and the pulse width was about 1.4 μs. The pulse width and the repetition rate of the Q-switched fiber laser can be changed along with the pump power. To the best of our knowledge, this is the first report of graphene saturable absorber for passively Q-switched 2 μm fiber lasers.     

10-W cladding-pumped fiber laser with single transverse mode output

A Yb-doped double-clad fiber laser is demonstrated with a measured power output of 10.6 W and a fundamental spatial mode. The optical-to-optical conversion efficiency is 44% and the slope efficiency is 86% closed to quantum efficiency of optical conversion. In our laser system, a D-shape (340 μm/400 μm) inner cladding Yb-doped fiber is used as the gain material within the Fabry-Perot cavity. Multimode diode pump radiation is injected into the cladding through an end facet of the composite fiber.     

Welding of polymers using a 2 μm thulium fiber laser

Absorber-free transmission and butt-welding of different polymers were performed using thulium fiber laser radiation at the wavelength 2 μm. The relations between the laser process conditions and the dimensions and quality of the seam were investigated by means of optical and phase-contrast microscopy. Mechanical properties of the weld joints were studied in tensile strength tests. Laser-welded polyethylene samples revealed a tensile strength of greater than 80% of the bulk material strength. Transmission welding of different polymer combinations featured the formation of different joint classes depending on the spectral properties. The experiments demonstrate new application areas of mid-IR fiber laser sources for materials processing.     

Collisional excitation X-ray laser experiments in plasmas produced by 0.53-μm and 0.35-μm laser light

Recent Ne- and Ni-like X-ray laser experiments carried out at the Centre d'Etudes de Limeil-Valenton (CEL-V) are reviewed. A variety of experiments in Ne-like X-ray lasers were performed; here we discuss measurements of soft X-ray amplification in Ge (Z=32) and Sr (Z=38) plasmas. In Ge plasmas produced by 0.53-m laser light at an irradiance of 6.0×10¹³ W/cm², gains between 2.2–2.5 cm^–1 on the 232.2 and 236.2 Å J=2–1 lines and a gain of 1.0 cm^–1 on the 196.1 Å J=0–1 line were measured. In addition, gains of 4.4 cm^–1 and 4.0 cm^–1 have been demonstrated on the J=2–1 transitions at 164.1 and 166.5 Å in Nelike Sr at laser intensities of 1.3×10¹⁴ W/cm². The effects of pumping the Ne-like Se X-ray laser with 0.35-m laser light have also been investigated; the Se lasing spectra is similar to that obtained with 0.53-m light. Experiments have also been carried out to optimize the gain of the 50.3 Å Ni-like Yb (Z=70) J=0–1 line. For Yb, no significant increase in gain over that previously reported was seen, but the time history of the Ni-like Yb X-ray laser was measured for the first time. Finally, attempts to extrapolate the Ni-like results to shorter wavelength were made using Ta (Z=73), W (Z=74), and Re (Z=75). No definitive observation of the Ni-like J=0–1 lasing lines was made in these experiments.     

Tm–Ho codoped fiber based all fiber amplification of a gain-switched 2 μm fiber laser

A Tm–Ho codoped fiber amplifier system is built. And, amplification of a gain-switched Tm–Ho codoped fiber laser is investigated. Average output of 300 mW is obtained at repetition rate of tens of kHz with an amplification gain bigger than 11 dB. And, pulse amplification efficiency of resonantly pumped Tm–Ho codoped single clad fiber is comparable with 793 nm pumped Tm-doped double clad fiber. The maximal pulse energy generated is about 13.1 μJ, corresponding to a peak power of 282 W at 20 kHz. During the amplification process, gain-switching, partially modulated gain-switched mode-locking and 100% modulated gain-switched mode-locking are observed sequentially. At gain-switching mode, the laser output enjoys a narrow linewidth of 0.31 nm, while at gain-switched mode-locking mode, the spectral linewidth broadens to 0.6 nm.     

High power single-mode large-mode-area photonic crystal fiber laser with improved Fabry-Perot cavity

An Yb3 -doped double-clad large-mode-area photonic crystal fiber (LMA PCF) laser with 103-W single-mode continuous-wave output power is demonstrated using an improved Fabry-Perot (F-P) configuration. The slope efficiency of 83.2% and good beam quality (M2 = 1.2±0.1) are achieved without any thermo-optical problems, dichroic mirror surface damage, and drop of the slope efficiency in this system.     

A 7-W diode-pumped Nd:YVO4 cw laser at 1.34 μm

A Nd:YVO₄ laser, end-pumped by a fiber-coupled diode-laser array, generates 7.3 W of output power at 1342 nm, the highest so far reported for this host crystal. The slope efficiency is 40% and the output-beam divergence is close to the diffraction limit. An important point in attaining such results is the choice of crystals with low Nd concentration. Received: 16 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +39-050/844333, E-mail: dilieto@df.unipi.it RID="**" ID="**"Permanent address: Scuola Normale Superiore, Piazza dei Cavalieri 7, Pisa, Italy