Thomas Calmano

Highly efficient Yb:YAG channel waveguide laser written with a femtosecond-laser

Using a femtosecond Ti:Sapphire laser, micro-tracks of material damage were written into Yb:YAG crystals. Waveguiding was achieved in a channel between pairs of tracks with guiding losses of 1.3 dB/cm at a wavelength of 1063 nm, due to a stress induced change of the refractive index. Pumped at a wavelength of 941 nm, highly efficient laser oscillation in a Yb:YAG channel waveguide at a wavelength of 1030 nm was demonstrated. An output power of 0.8 W at 1.2 W of launched pump power was achieved, resulting in a record slope efficiency of 75%.

Crystalline Waveguide Lasers in the Visible and Near-Infrared Spectral Range

This paper summarizes our recent results on crystalline waveguides and waveguide lasers fabricated by the femtosecond-laser writing technique. Highly efficient waveguide lasers emitting in the near infrared spectral range based on ytterbium and neodymium doped Y3Al5O12 with slope efficiencies above 70% and continuous wave output powers of more than 5 W were demonstrated. Furthermore, pulsed laser operation of passively Q-switched Yb:YAG and Nd:YAG wavequide lasers was achieved by incorporating the saturable absorber Cr4+:YAG in a monolithic setup. Based on fs-laser written curved structures in Yb:YAG, efficient curved waveguide lasers could be demonstrated. Also, waveguide lasers in the visible spectral range were investigated. We achieved laser emission in the green, orange, red and deep-red spectral region and could demonstrate output powers of more than 1 W with waveguides based on praseodymium doped materials. Additionally, switchable and dual wavelength operation between the orange and red laser emission was achieved. By utilizing the nonlinear crystal KTiOPO4 as substrate material for fs-laser inscription, nonlinear waveguides were realized. With these devices, efficient second harmonic generation into the blue and green spectral range was achieved.

Curved Yb:YAG waveguide lasers, fabricated by femtosecond laser inscription

Straight and s-curve Yb(7%):YAG waveguides have been fabricated with the femtosecond laser writing technique. By employing a novel writing scheme an increase of the refractive index change could be achieved in comparison to waveguides written with the standard procedure. Straight waveguides, fabricated with this scheme, enabled highly efficient Ti:sapphire laser pumped waveguide lasers with slope efficiencies of 79% and output powers of more than 1 W. With slope efficiencies from 50% to 60% for the curved waveguide lasers with radii of curvature of R ≥ 20 mm the possibility of fs-laser written complex optical devices is demonstrated.

Femtosecond-laser-written diode-pumped Pr:LiYF 4 waveguide laser

Waveguides were fabricated in a 5 mm long Pr(0.5 at%):LiYF4 (YLF) crystal with a femtosecond Ti:sapphire laser system. Waveguiding was achieved inside a core surrounded by eight single modified tracks building a rhombic structure. The waveguide was pumped at a wavelength of 444 nm with an InGaN laser diode. Orange and deep red laser oscillation were realized. Maximum output powers of 25 mW at 604 nm and 12 mW at 720 nm with respect to the incident pump power were achieved.

Crystalline Pr:SrAl 12 O 19 waveguide laser in the visible spectral region

We fabricated waveguides in Pr:SrAl(12)O(19) crystals by direct femtosecond laser writing. The propagation losses were calculated to be as low as 0.16 dB/cm at a wavelength of 633 nm. Laser oscillation in a diode-pumped waveguide at a wavelength of 643.5 nm was realized. The output power of the waveguide laser was 28.1 mW at a slope efficiency of 8%.

Diode pumped high power operation of a femtosecond laser inscribed Yb:YAG waveguide laser [Invited]

Waveguides were written into single crystalline Yb(7%):YAG with a femtosecond laser. Laser oscillation of the waveguides without external mirrors at an output coupling transmission of 99% was demonstrated. The laser performance of the waveguide lasers, pumped with various light sources, was examined. With an optically pumped semiconductor laser (OPS) as pump source a slope efficiency of 51% regarding incident pump power and a maximum output power of 1.76 W could be achieved. By using a high brightness DBR tapered diode laser as pump source the possible miniaturization of the waveguide laser device was demonstrated. With this pump source even 2.35 W of output power from the waveguide laser was achieved. The beam quality at highest output power turned out to be excellent with an M2-factor of less than 1.3.

Efficient visible laser operation of Pr,Mg:SrAl 12 O 19 channel waveguides

We report the fabrication and visible laser operation of Pr,Mg:SrAl12O19 waveguides. Waveguiding structures were created by focusing the radiation of a femtosecond Ti:sapphire laser into bulk material. Guiding losses were determined to be as low as 0.12 dB cm(-1) at 632.8 nm. By employing a frequency-doubled optically pumped semiconductor laser, waveguide laser operation was realized at wavelengths of 525.3, 644.0, and 724.9 nm with output powers as high as 36, 1065, and 504 mW, respectively. To the best of our knowledge this is the first demonstration of green laser operation in a Pr(3+)-doped crystalline waveguide laser.

Laser-written waveguides in KTP for broadband Type II second harmonic generation

Femto-second laser writing was used to fabricate waveguides in a z-cut KTP sample with losses below 0.8 dB/cm. They were used for efficient, broad bandwidth, Type II birefringent second harmonic generation to the green. The temperature and wavelength bandwidth were, 28 C ∙ cm and 0.85 nm ∙ cm, respectively.

Q-switched operation of a femtosecond-laser-inscribed Yb:YAG channel waveguide laser using carbon nanotubes

We demonstrate a diode-pumped femtosecond-laser-inscribed Yb:YAG channel waveguide laser, Q-switched by using single-walled carbon nanotubes (SWCNTs) near 1029 nm. We used saturable absorber mirrors (SAMs) fabricated by depositing SWCNTs on three different output couplers. Best performance of the 9.3-mm-long ultra-compact Q-switched waveguide laser is obtained with an output coupling transmission of 20%. In this case, a maximum average output power of 60 mW with a corresponding pulse energy of 37.7 nJ and a pulse duration of 88 ns at 1.59-MHz repetition rate were achieved. The highest pulse energy of 39.2 nJ and the shortest pulse duration of 78 ns were obtained with 30% and 10% output couplers, respectively.

Highly efficient continuous wave blue second-harmonic generation in fs-laser written periodically poled Rb:KTiOPO 4 waveguides

Waveguides were inscribed into a 9.5 mm long periodically poled KTiOPO4 crystal with a Ti:sapphire femtosecond-laser. Waveguiding was achieved between two parallel written tracks with spacings of 17-19 μm. The fundamental power of 1.6 W for frequency doubling in the waveguide was delivered by a continuous wave Ti:sapphire laser at a wavelength of 943.18 nm. A maximum output power of 76 mW in the blue spectral region was achieved. This corresponds to a single pass normalized conversion efficiency of 4.6%  W(-1) cm(-2).