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Numerical modelling of optical Stark effect saturable absorbers in mode-locked femtosecond VECSELs

Numerical modelling of optical Stark effect saturable absorbers in mode-locked femtosecond VECSELs
Numerical modelling of optical Stark effect saturable absorbers in mode-locked femtosecond VECSELs
Quasi-soliton modelocking has been identified as the mechanism responsible for the formation of picosecond pulses in passively mode-locked VECSELs, but neither this mechanism nor Kerr lens modelocking can account for the formation of sub-picosecond pulses from these lasers. Numerical simulations have shown that the optical Stark effect is capable of shortening pulses in the absence of bleaching, but to date no studies have been performed under realistic operating conditions. We model the interaction of an optical pulse with an absorbing quantum well using a semi-classical two level atom approximation. As the bandwidth of a VECSEL pulse is small compared to the spread of energies within a semiconductor band the population of two level atoms is divided into "live" atoms which interact with the optical field, and "dead" atoms which do not. Live and dead states are coupled by carrier-carrier scattering. Results from this model show an increase in pulse shortening above that due to saturable absorber bleaching at pulse durations below one picosecond, implying that an additional effect is responsible for the formation of femtosecond pulses. At these pulse durations the model predicts that the absorbing resonance broadens and decreases in amplitude. This is recognisable as a result of the optical Stark effect. The predictions of this model are compared to experimental results from several femtosecond VECSELs. For some modelocked VECSELs an excellent match between simulation and experiment is found, but in other cases the model cannot reproduce experimental results. We conclude that while the optical Stark effect may be the dominant pulse shaping mechanism in some modelocked VECSELs, others appear to be dominated by other effects.
SPIE
Quarterman, A.H.
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Daniell, G.J.
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Carswell, S.
615054b2-cd35-4a60-a9b6-e4017e5caddd
Wilcox, K.G.
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Mihoubi, Z.
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Chung, A.L.
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Apostolopoulos, V.
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Tropper, A.C.
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Keller, Ursula
Quarterman, A.H.
1d59a842-c64f-4274-a808-17b7700fe20c
Daniell, G.J.
36dd7055-af34-48c7-88a3-f2e5f633d52c
Carswell, S.
615054b2-cd35-4a60-a9b6-e4017e5caddd
Wilcox, K.G.
b7c8da76-3530-4cbf-aaec-ffa11c347230
Mihoubi, Z.
6b6bd3e0-663e-4264-83ab-dd68c6eaaa2c
Chung, A.L.
b548b7cc-c33a-45e4-8634-3c44a250d207
Apostolopoulos, V.
8a898740-4c71-4040-a577-9b9d70530b4d
Tropper, A.C.
f3505426-e0d5-4e91-aed3-aecdb44b393c
Keller, Ursula

Quarterman, A.H., Daniell, G.J., Carswell, S., Wilcox, K.G., Mihoubi, Z., Chung, A.L., Apostolopoulos, V. and Tropper, A.C. (2011) Numerical modelling of optical Stark effect saturable absorbers in mode-locked femtosecond VECSELs. Keller, Ursula (ed.) In Vertical External Cavity Surface Emitting Lasers (VECSELs). vol. 7919, SPIE. 7 pp . (doi:10.1117/12.874649).

Record type: Conference or Workshop Item (Paper)

Abstract

Quasi-soliton modelocking has been identified as the mechanism responsible for the formation of picosecond pulses in passively mode-locked VECSELs, but neither this mechanism nor Kerr lens modelocking can account for the formation of sub-picosecond pulses from these lasers. Numerical simulations have shown that the optical Stark effect is capable of shortening pulses in the absence of bleaching, but to date no studies have been performed under realistic operating conditions. We model the interaction of an optical pulse with an absorbing quantum well using a semi-classical two level atom approximation. As the bandwidth of a VECSEL pulse is small compared to the spread of energies within a semiconductor band the population of two level atoms is divided into "live" atoms which interact with the optical field, and "dead" atoms which do not. Live and dead states are coupled by carrier-carrier scattering. Results from this model show an increase in pulse shortening above that due to saturable absorber bleaching at pulse durations below one picosecond, implying that an additional effect is responsible for the formation of femtosecond pulses. At these pulse durations the model predicts that the absorbing resonance broadens and decreases in amplitude. This is recognisable as a result of the optical Stark effect. The predictions of this model are compared to experimental results from several femtosecond VECSELs. For some modelocked VECSELs an excellent match between simulation and experiment is found, but in other cases the model cannot reproduce experimental results. We conclude that while the optical Stark effect may be the dominant pulse shaping mechanism in some modelocked VECSELs, others appear to be dominated by other effects.

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More information

Published date: 21 February 2011
Venue - Dates: Conference on Vertical External Cavity Surface Emitting Lasers (VECSELs), , San Francisco, United States, 2011-01-24 - 2011-01-25

Identifiers

Local EPrints ID: 444477
URI: http://eprints.soton.ac.uk/id/eprint/444477
PURE UUID: 08072682-bf87-4a37-a91a-0d63dc28e23e
ORCID for V. Apostolopoulos: ORCID iD orcid.org/0000-0003-3733-2191

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Date deposited: 20 Oct 2020 16:35
Last modified: 18 Feb 2021 17:10

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Contributors

Author: A.H. Quarterman
Author: G.J. Daniell
Author: S. Carswell
Author: K.G. Wilcox
Author: Z. Mihoubi
Author: A.L. Chung
Author: A.C. Tropper
Editor: Ursula Keller

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