We report a diode-pumped ultrafast Ti:sapphire laser tunable over a 50 nm range. Sub-100 fs pulses are generated at a pulse repetition rate of 139 MHz with a maximum average output power of 430 mW

Coyle, Jamie C. E.

Hopkins, John-Mark

Kemp, Alan J.

Lagatsky, Alexander A.

University of Strathclyde Institutional Repository

Ultrafast diode-pumped Ti:sapphire lasers Abstract: We report a diode-pumped ultrafast Ti:sapphire laser tunable over a 120 nm range. Sub-100 fs pulses are generated at a pulse repetition rate of 135 MHz with a maximum average output power of 430 mW. A Broadly Tunable Ultrafast Diode-Pumped Ti:sapphire Laser Fraunhofer Centre for Applied Photonics Jamie C. E. Coyle1,2, Alan J. Kemp2, John-Mark Hopkins1 and Alexander A. Lagatsky1 1. Fraunhofer Centre for Applied Photonics, Fraunhofer UK Research Ltd, 99 George Street, Glasgow, G1 1RD, UK. 2. Institute of Photonics, Dept. of Physics, University of Strathclyde, 99 George Street, Glasgow, G1 1RD, UK. Experimental setup Conclusion Mode-locking mechanisms Here we report to the best of our knowledge the first broadly tunable diode-pumped ultrafast Ti:sapphire laser. Laser experiments include two different mode-locking approaches: one using a semiconductor saturable absorber mirror (SESAM) and one using Kerr-lens mode-locking. The experimental setup was optimised for SESAM mode-locking by ensuring the cavity operated in the middle of stability zone II, thus creating a second cavity mode waist on the SESAM. The same configuration was used for KLM by replacing the SESAM with a high reflector mirror and moving to the edge of cavity stability. KLM was then initiated by translating one of the folding mirrors towards the crystal. References 1. P. W. Roth, D. Burns, and A. J. Kemp, “Power scaling of a directly diode-laser-pumped Ti:sapphire laser,” Opt. Express 20, 20629–20634 (2012). 2. K. Gürel, V. J. Wittwer, M. Hoffmann, C. J. Saraceno, S. Hakobyan, B. Resan, A. Rohrbacher, K. Weingarten, S. Schilt, and T. Südmeyer, “Green-diode-pumped femtosecond Ti:Sapphire laser with up to 450 mW average power,” Opt. Express 23, 30043-30048 (2015). 3. A. Rohrbacher, O. E. Olarte, V. Villamaina, P. Loza-Alvarez, and B. Resan, “Multiphoton imaging with blue-diode-pumped SESAM-modelocked Ti:sapphire oscillator generating 5 nJ 82 fs pulses,” Opt. Express 25, 10677-10684 (2017). Acknowledgements: This work was funded by UK Engineering and Physical Sciences Research Council (EPSRC), via the Centre for Doctoral Training in Applied Photonics and Fraunhofer UK Research Limited. AJK acknowledges support from the Royal Academy of Engineering. In conclusion, we have demonstrated average output power as high as 430 mW, pulses as short as 85 fs and tunability as wide as 50 nm (2% OC) for the SESAM mode-locked  Ti:sapphire laser. When operated in a KLM regime we were able to achieve a tuning range up to 120 nm, and output power as high as 158 mW. In the case of the SESAM setup tunability was limited by the SESAM reflectivity range, rather than the gain bandwidth of Ti:sapphire. For the KLM configuration, work is underway to further optimise the current setup. Alternatively, wide bandwidth novel saturable absorber materials, such as graphene could be used as a mode-locking element. SESAM mode-locking results KLM results Laser experiments were performed with a Brewster-cut 4.8 mm long, 3 mm × 3 mm aperture Ti:sapphire crystal, FOM>200, Single pass absorption at 450 nm = 64%, α450  nm = 2.13 cm-1.  LD1 and LD2: 3.5 W, 450 nm, 28×1 µm emitting area. Pump Focusing Optics: aspheric lens (f = 4.51 mm), concave cylindrical lens (f = -9.7 mm), convex cylindrical lens (f = 80 mm). FL1: achromatic doublet lens (f = 100 mm). FL2: achromatic doublet lens (f = 75 mm).  M1 and M2: dichroic high-reflecting folding mirrors, 75 mm ROC. DCM: double chirped mirror, -120 fs2 per bounce, GDD = -960 fs2. Prism: fused silica prism pair, tip-to-tip separation = 50 cm, 4 mm insertion, GDD = -677 fs2. Net cavity GDD: 556 fs2 (crystal) - 960 fs2 (DCM) - 667 fs2 (prism pair) = -1087 fs2. OC: output coupler, 2% and 5% for SESAM setup, 1% for the KLM setup. SESAM: distributed Bragg reflector structure with a GaAs quantum well, low-signal absorption was ~97.5% over the range of 775-840 nm, and non-saturable losses are <1%.   Pump beam waist radii: LD1: 39×13 µm, and LD2: 30×11 µm. Laser cavity mode radii in the crystal: 29×16 µm. Laser cavity mode radius on the SESAM: 85 µm. Pump setup Pump power ML mechanism Self-starting Output Power Pulse Duration Tunability Reference 2 × 452 nm 2 × 1 W SESAM Yes 101 mW 111 fs No [1] 2 × 520 nm 2 × 1 W 2 × 1.5 W SESAM KLM Yes No 200 mW 450 mW 68 fs 39 fs No [2] 2 × 450 nm 2 × 2.9 W SESAM Yes 460 mW 65 fs No [3] 2 × 450 nm 2 × 3.5 W SESAM KLM Yes No 430 mW 158 mW 85 fs 38 fs 50 nm 120 nm This work Input – output characteristics Tuning range Optical spectrum Corresponding autocorrelation RF spectrum Input – output characteristics Tuning range Optical spectrum Corresponding autocorrelation RF spectrum 

A broadly tunable ultrafast diode-pumped Ti:sapphire laser

https://strathprints.strath.ac.uk/63476/1/Coyle_etal_ASSL_2017_A_broadly_tunable_ultrafast_diode_pumped.pdf

A broadly tunable ultrafast diode-pumped Ti:sapphire laser

Abstract

Similar works

Full text

Available Versions

University of Strathclyde Institutional Repository