Unveiling second harmonic generation from femtosecond-laser microstructured Nd:YAG crystal.

In this work we apply second harmonic microscopy to the analysis of damage tracks inscribed by femtosecond laser irradiation in a Nd:YAG crystal. While second harmonic generation is not expected in the bulk of this centrosymmetric material, the 2D and 3D images obtained via second harmonic microscopy show that the induced micro-modification of the crystal structure leads to a localized generation of the nonlinear signal. The nature of this modification and its dependence on irradiation and detection parameters is discussed. These findings demonstrate the capability of second harmonic microscopy for the morphological analysis of written structures in Nd:YAG and open the door for the design and fabrication of new nonlinear structures to be integrated in novel photonic devices.

In-band pumped Kerr-lens mode-locked Tm,Ho-codoped calcium aluminate laser.

We report on a Kerr-lens mode-locked Tm,Ho-codoped calcium aluminate laser with in-band pumping of the Tm ions by a spatially single-mode 1678 nm Raman fiber laser. The structurally disordered CaGdAlO4 host crystal is also codoped also with the passive Lu ion for additional inhomogeneous line broadening. The Tm,Ho,Lu:CaGdAlO4 laser generates soliton pulses as short as 79 fs at a central wavelength of 2073.6 nm via soft-aperture Kerr-lens mode-locking. The corresponding average output power amounts to 91 mW at a pulse repetition rate of ∼86 MHz. The average output power can be scaled to 842 mW at the expense of slightly longer pulses of 155 fs at 2045.9 nm, which corresponds to a peak power of ∼58 kW. To the best of our knowledge, this represents the first demonstration of an in-band pumped Kerr-lens mode-locked Tm,Ho solid-state laser at ∼2 µm.

Growth, spectroscopy and laser operation of Tm,Ho:GdScO3 perovskite crystal.

We report on the growth, polarized spectroscopy and first laser operation of an orthorhombic (space group Pnma) Tm3+,Ho3+-codoped gadolinium orthoscandate (GdScO3) perovskite-type crystal. A single crystal of 3.76 at.% Tm, 0.35 at.% Ho:GdScO3 was grown by the Czochralski method. Its polarized absorption and fluorescence properties were studied revealing a broadband emission around 2 µm. The parameters of the Tm3+ ↔ Ho3+ energy transfer was quantified, P28 = 1.30 × 10-22 cm3µs-1, and P71 = 0.99 × 10-23 cm3µs-1, and the thermal equilibrium lifetime was measured to be 3.5 ms. The crystal-field splitting of Tm3+ and Ho3+ multiplets in Cs symmetry sites of the perovskite structure was determined by low-temperature spectroscopy and the mechanism of spectral line broadening is discussed. The continuous-wave Tm,Ho:GdScO3 laser generated 1.16 W at ∼2.1 µm with a slope efficiency of 50.5%, a laser threshold of 184 mW, a linear laser polarization (E || c) and a spatially single-mode output. The Tm,Ho:GdScO3 crystal is promising for broadly tunable and femtosecond mode-locked lasers emitting above 2 µm.

SESAM mode-locked Yb:GdScO3 laser.

We report on the investigation of continuous-wave (CW) and SEmiconductor Saturable Absorber Mirror (SESAM) mode-locked operation of a Yb:GdScO3 laser. Using a single-transverse-mode, fiber-coupled InGaAs laser diode at 976 nm as a pump source, the Yb:GdScO3 laser delivers 343 mW output power at 1062 nm in the CW regime, which corresponds to a slope efficiency of 52%. Continuous tuning is possible across a wavelength range of 84 nm (1027-1111 nm). Using a commercial SESAM to initiate mode-locking and stabilize soliton-type pulse shaping, the Yb:GdScO3 laser produces pulses as short as 42 fs at 1065.9 nm, with an average output power of 40 mW at 66.89 MHz. To the best of our knowledge, this is the first demonstration of passively mode-locking with Yb:GdScO3 crystal.

Continuous-wave and SESAM mode-locked operation of a Yb:YSr3(PO4)3 laser.

We report on the continuous-wave (CW) and, for what we believe to be the first time, passively mode-locked (ML) laser operation of an Yb3+-doped YSr3(PO4)3 crystal. Utilizing a 976-nm spatially single-mode, fiber-coupled laser diode as pump source, the Yb:YSr3(PO4)3 laser delivers a maximum CW output power of 333 mW at 1045.8 nm with an optical efficiency of 55.7% and a slope efficiency of 60.9%. Employing a quartz-based Lyot filter, an impressive wavelength tuning range of 97 nm at the zero level was achieved in the CW regime, spanning from 1007 nm to 1104 nm. In the ML regime, incorporating a commercially available semiconductor saturable absorber mirror (SESAM) to initiate and maintain soliton-like pulse shaping, the Yb:YSr3(PO4)3 laser generated pulses as short as 61 fs at 1062.7 nm, with an average output power of 38 mW at a repetition rate of ∼66.7 MHz.

Growth, spectroscopy and SESAM mode-locking of a "mixed" Yb:Ca(Gd,Y)AlO4 disordered crystal.

We present the growth, spectroscopy, continuous-wave (CW) and passively mode-locked (ML) operation of a novel "mixed" tetragonal calcium rare-earth aluminate crystal, Yb3+:Ca(Gd,Y)AlO4. The absorption, stimulated-emission, and gain cross-sections are derived for π and σ polarizations. The laser performance of a c-cut Yb:Ca(Gd,Y)AlO4 crystal is studied using a spatially single-mode, 976-nm fiber-coupled laser diode as a pump source. A maximum output power of 347 mW is obtained in the CW regime with a slope efficiency of 48.9%. The emission wavelength is continuously tunable across 90 nm (1010 - 1100 nm) using a quartz-based Lyot filter. With a commercial SEmiconductor Saturable Absorber Mirror to initiate and maintain ML operation, soliton pulses as short as 35 fs are generated at 1059.8 nm with an average output power of 51 mW at ∼65.95 MHz. The average output power can be scaled to 105 mW for slightly longer pulses of 42 fs at 1063.5 nm.

Cascade laser optimization for 3H4 → 3H5 and 3F4 → 3H6 sequent transitions in Tm3+-doped materials.

We study a cascade laser scheme involving the 3H4 → 3H5 and 3F4 → 3H6 consecutive transitions in Tm3+-doped materials as a promising technique to favor laser emission at 2.3 µm. We examine the conditions in terms of the Tm3+ doping levels for which the cascade laser is beneficial or not. For this, Tm:LiYF4 lasers based on crystals with several doping levels in the range of 2.5 - 6 at.% with and without cascade laser are studied. For low doping of 2.5 at.% Tm3+, adding the laser emission at 1.9 µm allows to double the output power at 2.3 µm, whereas for high doping of 6 at.%, allowing the laser to operate at 1.9 µm totally suppresses the laser emission at 2.3 µm. An analytical model is developed and confronted with experimental results to predict this doping-dependent phenomenon and forecast the potential benefits. This study of cascade laser emission on the 3H4→ 3H5 and 3F4→ 3H6 transitions versus the Tm3+ doping level is finally extended to other well-known Tm3+-doped laser materials.

Kerr-lens mode-locking of an Yb:CLNGG laser.

We report on a Kerr-lens mode-locked laser based on an Yb3+-doped disordered calcium lithium niobium gallium garnet (Yb:CLNGG) crystal. Pumping by a spatially single-mode Yb fiber laser at 976 nm, the Yb:CLNGG laser delivers soliton pulses as short as 31 fs at 1056.8 nm with an average output power of 66 mW and a pulse repetition rate of ∼77.6 MHz via soft-aperture Kerr-lens mode-locking. The maximum output power of the Kerr-lens mode-locked laser amounted to 203 mW for slightly longer pulses of 37 fs at an absorbed pump power of 0.74 W, which corresponds to a peak power of 62.2 kW and an optical efficiency of 20.3%.

Excited-state absorption and upconversion pumping of Tm3+-doped potassium lutetium double tungstate.

We report on a bulk thulium laser operating on the 3H4 → 3H5 transition with pure upconversion pumping at 1064 nm by an ytterbium fiber laser (addressing the 3F4 → 3F2,3 excited-state absorption (ESA) transition of Tm3+ ions) generating 433 mW at 2291 nm with a slope efficiency of 7.4% / 33.2% vs. the incident / absorbed pump power, respectively, and linear laser polarization representing the highest output power ever extracted from any bulk 2.3 µm thulium laser with upconversion pumping. As a gain material, a Tm3+-doped potassium lutetium double tungstate crystal is employed. The polarized ESA spectra of this material in the near-infrared are measured by the pump-probe method. The possible benefits of dual-wavelength pumping at 0.79 and 1.06 µm are also explored, indicating a positive effect of co-pumping at 0.79 µm on reducing the threshold pump power for upconversion pumping.

Diode-pumped mode-locked Yb:Sc2SiO5 laser generating 38 fs pulses.

We report on sub-40 fs pulse generation from a Yb:Sc2SiO5 laser pumped by a spatially single-mode fiber-coupled laser diode at 976 nm. A maximum output power of 545 mW was obtained at 1062.6 nm in the continuous-wave regime, corresponding to a slope efficiency of 64% and a laser threshold of 143 mW. A continuous wavelength tuning across 80 nm (1030 -1110 nm) was also achieved. Implementing a SESAM for starting and stabilizing the mode-locked operation, the Yb:Sc2SiO5 laser delivered soliton pulses as short as 38 fs at 1069.5 nm with an average output power of 76 mW at a pulse repetition rate of ∼79.8 MHz. The maximum output power was scaled to 216 mW for slightly longer pulses of 42 fs, which corresponded to a peak power of 56.6 kW and an optical efficiency of 22.7%. To the best of our knowledge, these results represent the shortest pulses ever achieved with any Yb3+-doped rare-earth oxyorthosilicate crystal.

56-fs diode-pumped SESAM mode-locked Yb:YAl3(BO3)4 laser.

We report on the first sub-60 fs pulse generated from a diode-pumped SESAM mode-locked Yb-laser based on a non-centrosymmetric Yb:YAl3(BO3)4 crystal as a gain medium. In the continuous-wave regime, pumping with a spatially single-mode, fiber-coupled 976 nm InGaAs laser diode, the Yb:YAl3(BO3)4 laser generated 391 mW at 1041.7 nm with a slope efficiency as high as 65.1%, and a wavelength tuning across 59 nm (1019 to 1078 nm) was achieved. By implementing a commercial SESAM to initiate and sustain the soliton type mode-locking, and using only a 1 mm-thick laser crystal, the Yb:YAl3(BO3)4 laser delivered pulses as short as 56 fs at a central wavelength of 1044.6 nm with an average output power of 76 mW at a pulse repetition rate of ∼67.55 MHz. To the best of our knowledge, this result represents the shortest pulses ever achieved from Yb:YAB crystal.

Sub-50 fs diode-pumped SESAM mode-locked Yb:SrF2 laser.

We report on sub-50 fs pulse generation from a passively mode-locked Yb:SrF2 laser pumped with a spatially single-mode, fiber-coupled laser diode at 976 nm. In the continuous-wave regime, the Yb:SrF2 laser generated a maximum output power of 704 mW at 1048 nm with a threshold of 64 mW and a slope efficiency of 77.2%. A continuous wavelength tuning across 89 nm (1006 - 1095 nm) was achieved with a Lyot filter. By implementing a SEmiconductor Saturable Absorber Mirror (SESAM) for initiating and sustaining the mode-locked operation, soliton pulses as short as 49 fs were generated at 1057 nm with an average output power of 117 mW at a pulse repetition rate of ∼75.9 MHz. The maximum average output power of the mode-locked Yb:SrF2 laser was scaled up to 313 mW for slightly longer pulses of 70 fs at 1049.4 nm, corresponding to a peak power of 51.9 kW and an optical efficiency of 34.7%.

Orange surface waveguide laser in Pr:LiYF4 produced by a femtosecond laser writing.

Depressed-cladding surface channel waveguides were inscribed in a 0.5 at.% Pr:LiYF4 crystal by femtosecond Direct Laser Writing. The waveguides consisted of a half-ring cladding (inner diameter: 17 µm) and side structures ("ears") improving the mode confinement. The waveguide propagation loss was as low as 0.14 ± 0.05 dB/cm. The orange waveguide laser operating in the fundamental mode delivered 274 mW at 604.3 nm with 28.4% slope efficiency, a laser threshold of only 29 mW and linear polarization (π), representing record-high performance for orange Pr waveguide lasers.

Semiconductor saturable absorber mirror mode-locked Yb:YAP laser.

We report on sub-30 fs pulse generation from a semiconductor saturable absorber mirror mode-locked Yb:YAP laser. Pumping by a spatially single-mode Yb fiber laser at 979 nm, soliton pulses as short as 29 fs were generated at 1091 nm with an average output power of 156 mW and a pulse repetition rate of 85.1 MHz. The maximum output power of the mode-locked Yb:YAP laser amounted to 320 mW for slightly longer pulses (32 fs) at an incident pump power of 1.52 W, corresponding to a peak power of 103 kW and an optical efficiency of 20.5%. To the best of our knowledge, this result represents the shortest pulses ever achieved from any solid-state Yb laser mode-locked by a slow, i.e., physical saturable absorber.

Diode-pumped SESAM mode-locked Yb:(Y,Gd)AlO3 laser.

We report on the continuous-wave (CW) and mode-locked (ML) laser performance of an Yb3+-doped yttrium-gadolinium orthoaluminate crystal, Yb:(Y,Gd)AlO3. Pumping by a single-transverse-mode fiber-coupled 976 nm InGaAs laser diode, the maximum output power in the CW regime amounted to 429 mW at 1041.8 nm corresponding to a slope efficiency of 51.1% and a continuous wavelength tuning across 84 nm (1011-1095 nm) was achieved. The self-starting ML operation of the Yb:(Y,Gd)AlO3 laser was stabilized by a semiconductor saturable absorber mirror. Soliton pulses as short as 43 fs were generated at 1052.3 nm with an average output power of 103 mW and a pulse repetition rate of ∼70.8 MHz. To the best of our knowledge, our result represents the first report on the passively mode-locked operation of a Yb:(Y,Gd)AlO3 laser, and the shortest pulse duration ever achieved from any Yb3+-doped orthorhombic perovskite aluminate crystals.

Soliton mode-locked Yb:Ca3Gd2(BO3)4 laser.

We report on a soliton mode-locked Yb:Ca3Gd2(BO3)4 laser at ∼1.06 µm stabilized by a semiconductor saturable absorber mirror. Pumping with a single-transverse mode, fiber-coupled laser diode at 976 nm, the Yb:Ca3Gd2(BO3)4 laser delivers soliton pulses as short as 39 fs at a central wavelength of 1059.2 nm with an average output power of 70 mW and a pulse repetition rate of ∼67.3 MHz.

SESAM mode-locked Yb:Sr3Y2(BO3)4 laser.

We demonstrate the first sub-40 fs soliton pulse generation from a diode-pumped Yb:Sr3Y2(BO3)4 laser passively mode-locked by a semiconductor saturable absorber mirror. Pulses as short as 38 fs at a central wavelength of 1051.7 nm were achieved with an average output power of 115 mW and a pulse repetition rate of 67.7 MHz. The maximum average output power reached 303 mW at 1057.8 nm with a slightly longer pulse duration of 52 fs, which corresponded to a peak power of 76.9 kW and an optical efficiency of 25.3%.

Diode-pumped mode-locked Yb:BaF2 laser.

We report on a continuous-wave (CW) and passively mode-locked operation of a fluorite-type Yb:BaF2 crystal. Pumped with a spatially single-mode, fiber-coupled InGaAs laser diode at 976 nm, the Yb:BaF2 laser generated a maximum CW output power of 512 mW at 1054.4 nm, corresponding to a laser threshold of 36.5 mW and a slope efficiency of 65.0%. A continuous wavelength tuning across 85 nm (1007-1092 nm) was achieved. By implementing a semiconductor saturable absorber mirror for initiating and sustaining the soliton pulse shaping, near Fourier-transform-limited pulses as short as 52 fs were generated at 1058.2 nm with an average output power of 129 mW at a pulse repetition rate of ∼79.5 MHz. To the best of our knowledge, this is the first report on the passively mode-locked operation of the Yb:BaF2 crystal.

Polarized spectroscopy and SESAM mode-locking of Tm,Ho:CALGO.

A Tm,Ho:CALGO laser passively mode-locked by a GaSb-based SESAM generated pulses as short as 52 fs at a central wavelength of 2015 nm with a broad spectral bandwidth of 82 nm (full width at half maximum) owing to the combined gain profiles of both dopants for σ-polarized light. The average output power reached 376 mW at a repetition rate of 85.65 MHz. In the continuous-wave regime, the laser was power scaled up to 1.01 W at 2080.6 nm with a slope efficiency of 32.0%, a laser threshold of 155 mW and π-polarized emission. Polarized spectroscopic properties of Ho3+ ions in singly doped and codoped CALGO crystals were revisited to explain the observed laser performance.

Kerr-lens mode-locked Yb:YAlO3 laser generating 24-fs pulses at 1085 nm.

We report on a Kerr-lens mode-locked Yb:YAlO3 laser generating soliton pulses as short as 24 fs at 1085 nm with an average output power of 186 mW and a pulse repetition rate of 87.5 MHz, representing the shortest pulses ever achieved from any mode-locked laser based on Yb3+-doped structurally ordered crystal. Optimized for power-scalable operation, the Yb:YAlO3 laser delivers 1.9 W at 1060 nm at the expense of a longer pulse duration of 44 fs, corresponding to a peak power of 462 kW and an optical efficiency of 43.2%.