Single-walled carbon nanotube saturable absorber assisted high-power mode-locking of a Ti:sapphire laser

In Hyung Baek,Hwang Woon Lee,Valdas Pasiskevicius,Valentin Petrov,Fabian Rotermund,Kihong Kim,Antonio Agnesi,Dong-Il Yeom,Sun Young Choi,Won Bae Cho

doi:10.1364/oe.19.007833

Abstract

We report on passive mode-locking of a Ti:sapphire laser employing a single-walled carbon nanotube saturable absorber (SWCNT-SA) specially designed and fabricated for wavelengths near 800 nm. Mode-locked pulses as short as 62 fs were generated at a repetition rate of 99.4 MHz. We achieved output powers from the SWCNT-SA mode-locked laser as high as 600 mW with a slope efficiency of 26%. The characteristics of SWCNT-SA-assisted mode-locking were compared with those of Kerr-lens mode-locking without SWCNT-SA.

Highlights

Ti:sapphire lasers operating near 800 nm are widely exploited in laboratories as ultrafast light sources for a variety of applications
The combination of Kerr lens mode-locking (KLM) and semiconductor saturable absorber mirrors (SESAMs) can ensure self-starting and stable operation of mode-locked Ti:sapphire lasers [5,8], but relatively high cost and complex manufacturing processes limited the wide use of such SESAMs
We present passive mode-locking of a Ti:sapphire laser, generating 62 fs pulses by intra-cavity chirp compensation, with a transmission-type SWCNT-SA optimized for 800 nm

Summary

Introduction

Ti:sapphire lasers operating near 800 nm are widely exploited in laboratories as ultrafast light sources for a variety of applications. The combination of KLM and SESAM can ensure self-starting and stable operation of mode-locked Ti:sapphire lasers [5,8], but relatively high cost and complex manufacturing processes limited the wide use of such SESAMs. Passive mode-locking techniques employing single-walled carbon nanotube saturable absorbers (SWCNT-SAs) have been extensively investigated as an alternative since the first demonstration of mode-locking in a fiber laser in 2004 [9]. Output power of only 45 mW was obtained at quite a high pump power of 4 W and there was no intra-cavity dispersion compensation This low power was a consequence of the high intra-cavity losses and damage limitation of the SWCNT-based saturable absorber used. The characteristics of the mode-locked regime, such as threshold, stability, pulse durations and spectral bandwidths are compared with those of pure KLM, i. e. mode-locking without the SWCNT-SA

Characteristics of SWCNT-SA

Experimental setup

Mode-locked operation

Conclusion