F. M. Bain

Ultrafast laser inscribed Yb:KGd(WO4)2 and Yb:KY(WO4)2 channel waveguide lasers.

We demonstrate laser action in diode-pumped microchip monolithic cavity channel waveguides of Yb:KGd(WO(4))(2) and Yb:KY(WO(4))(2) that were fabricated by ultrafast laser writing. The maximum output power achieved was 18.6 mW with a threshold of approximately 100 mW from an Yb:KGd(WO(4))(2) waveguide laser operating at 1023 nm. The propagation losses for this waveguide structure were measured to be 1.9 dBcm(-1).

Continuous-wave and Q-switched operation of a compact, diode-pumped Yb3+:KY(WO4)2 planar waveguide laser.

A diode-pumped LPE-grown Yb:KYW planar waveguide laser is demonstrated in a microchip monolithic cavity configuration. Output powers as high as 148 mW and thresholds as low as 40 mW were demonstrated during continuous-wave operation. Pulses of 170 ns duration with maximum pulse energy of 44 nJ at a 722 kHz repetition rate were generated when Q-switched using a semiconductor saturable absorber mirror.

Low-loss quantum-dot-based saturable absorber for efficient femtosecond pulse generation

We report the efficient generation of femtosecond pulses from a diode-pumped solid-state laser that has been passively mode locked using a quantum-dot-based saturable absorber. Average output powers up to 1.15W and transform-limited pulses as short as 114fs were obtained around 1040nm with a pulse repetition frequency of 107MHz from a diode-pumped Yb3+:KY(WO4)2 laser. The InGaAs quantum-dot saturable absorber was characterized to have a saturation fluence of 25μJ∕cm2 and nonsaturable losses of less than 0.2% with an initial low-signal absorption of 2.5% at 1040nm.

Lasing action at around 1.9 μm from an ultrafast laser inscribed Tm-doped glass waveguide

We report optical guiding and laser action at around 1.9 μm in a Tm³⁺-doped fluorogermanate glass waveguide fabricated using ultrafast laser inscription. A monolithic laser cavity was constructed by directly butt coupling dielectric mirrors to each facet of the 6.0 mm long Tm³⁺-doped waveguide. When the waveguide was pumped by a Ti:sapphire laser tuned to 791 nm, laser oscillation was achieved at around 1.91 μm. This waveguide laser exhibited a maximum slope efficiency of 6% and a maximum output power of 32 mW when pumped with 620 mW of incident laser power.

Microspectroscopy of ultrafast laser inscribed channel waveguides in Yb:tungstate crystals

We report microspectroscopy measurements of crystalline channel waveguides fabricated in Yb:KGd(WO4)2 and Yb:KY(WO4)2 using the ultrafast laser inscription technique. From these measurements we find that densification of the WO2W bridge in the double tungstate crystal lattice is responsible for the refractive index increase, which creates the waveguide confinement. We identified that shifts toward lower energies in the ∼760 cm−1 Raman mode indicate regions, which guide light polarized along the crystallographic b axis, while higher energy shifts in the 682 and 898 cm−1 Raman lines correspond to guiding regions for light polarized along the crystallographic a axis.

High-power Kerr-lens mode-locked ytterbium lasers

Progress in the development of efficient and reliable diode-pumped ytterbium femtosecond laser systems based on Kerr-lens mode locking effect is reported. Average output power of up to 1 W is demonstrated in a Kerr-lens mode locked Yb:YVO4 laser with pulse durations as short as 80 fs at a pulse repetition frequency of 79 MHz. Measurements of the nonlinear refractive indexes of the Yb3+:YVO4 crystal, n2, were performed and were determined to be 39×10-16 cm2/W and 49×10-16 cm2/W for E||c and E⊥c polarizations, respectively. These results were found to be in a good agreement with those calculated using both the Kramers-Krönig relation and Boling, Glass and Owyoung formula. Keywords: Mode-locked lasers, diode-pumped lasers 1.

Advances in femtosecond lasers having enhanced efficiencies

Progress in the development of efficient and reliable diode-pumped femtosecond laser systems based on both Kerr-lens and saturable-absorber mode locking is reported. Efficient Kerr-lens mode locking in diode pumped ytterbium-doped lasers, namely Yb:KY(WO4)2 (Yb:KYW) and Yb:YVO4, is demonstrated with average output powers in excess of 1W, pulse durations around 100fs and electrical-to-optical efficiencies that exceed 15%. Novel semiconductor saturable absorbers based on InAs/InGaAs quantum dots are described and their applicability for efficient femtosecond pulse generation from near-infrared solid-state lasers is discussed. Efficient passive mode locking in the spectral regions around 1.3&mgr;m and 1.55&mgr;m in Cr:forsterite and the more recently developed Er, Yb:YAl3(BO4)3 crystalline lasers has been demonstrated using low-loss InGaNAs saturable absorbers. A few examples of applications for this category of robust and efficient femtosecond lasers have been included. Specifically, the characteristics of a femtosecond visible light source producing pulses as short as 200fs at 520nm are outlined.

Holographic recording of sub-micron period gratings and photonic crystals in the photoresist SU8

SU8 is a commercial negative photoresist, which is highly transparent in the visible and near-infrared and extremely resistant to many organic solvents. Here we show that sub-micron period diffraction gratings, and 2D photonic crystal structures, can be readily formed holographically over extended areas. By coating the SU8 layer with a suitable gain medium, such structures may be used as feedback and output-coupling gratings for organic waveguide lasers. Thin films of SU8, were initially deposited by spin casting onto glass substrates. These films were then mounted in one arm of a Lloyds mirror interferometer and exposed with the expanded beam of a HeCd laser, operating at 325 nm. Subsequent baking and developing steps lead to both volume gratings with index contrast of 0.014, and surface gratings with corrugation depths of up to 140 nm. By varying the incidence angle of the HeCd laser beam to the SU8 film we have tuned the microstructure period from 500 nm down to 200 nm. Using multiple exposures, both doubly-periodic diffraction gratings and square-lattice crystal structures have been produced.

Micro-luminescence and micro-Raman mapping of ultrafast laser inscribed Yb:KGd(WO 4 ) 2 and Yb:KY(WO 4 ) 2 channel waveguides

Micro-luminescence and micro-Raman mapping has been performed on ultrafast laser inscribed channel Yb:KGd(WO<inf>4</inf>)<inf>2</inf> and Yb:KY(WO<inf>4</inf>)<inf>2</inf> waveguides. Correlation can be seen between guiding regions and shifts in micro-luminescence and micro-Raman peaks when compared to the bulk.

1-μm and 1.3-μm femtosecond lasers mode-locked using quantum-dot-based saturable absorbers

We report on the generation of femtosecond pulses in the 1-μm and 1.3-μm spectral regions from Yb:KYW and Cr:forsterite lasers, respectively, where InAs/InGaAs quantum dot based saturable absorber mirrors (QD-SAMs) have been utilised. For the experimental observations reported here, cw Yb:KYW and Cr:forsterite lasers pumped by a tapered 980nm laser diode and a Nd:YVO4 laser at 1064nm, respectively, were constructed and evaluated. Highly asymmetric Z-fold laser cavities were configured for both laser systems. During continuous wave operation the Yb:KYW laser produced an output power of 2W (3.5W incident power) at 1047nm and 250mW of average power (6W incident power) was generated by Cr:forsterite laser at 1270nm.