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Multiple-beam interference patterns in optical fiber generated with ultrafast pulses and a phase mask
Christopher W Smelser1, Stephen J Mihailov, Dan Grobnic
1Communications Research Centre Canada, 3701 Carling Avenue, P.O. Box 11490, Station H, Ottawa, Ontario, Canada K2H 8S2. christopher.smelser@crc.ca
Optics Letters
|July 21, 2004
Summary
We compared ultrafast laser cladding patterns to a beam interference model. Femtosecond pulses require considering bandwidth and pulse effects like group-velocity walk-off for accurate pattern prediction.
Area of Science:
- Optics and Photonics
- Laser Material Processing
Background:
- Grating structures are fabricated using ultrafast lasers and phase masks.
- Understanding cladding patterns is crucial for controlling grating properties.
Purpose of the Study:
- To compare cladding patterns from ultrafast laser fabrication with a continuous wave (cw) beam interference model.
- To investigate the influence of pulse characteristics on pattern formation in femtosecond laser fabrication.
Main Methods:
- Fabrication of grating structures using ultrafast lasers (picosecond and femtosecond) and a phase mask.
- Modeling of cladding patterns using a cw beam interference model.
- Analysis of the impact of pulse bandwidth and group-velocity walk-off on pattern formation.
Main Results:
- Observed cladding patterns for picosecond pulses agree well with the cw beam interference model.
- For femtosecond pulses, deviations from the model occur due to the full bandwidth and pulsed nature of the source.
- Group-velocity walk-off significantly affects cladding patterns in the femtosecond regime.
Conclusions:
- The cw beam interference model is adequate for picosecond pulse fabrication but insufficient for femtosecond pulses.
- Femtosecond pulse characteristics, including group-velocity walk-off, must be incorporated for accurate modeling.
- Femtosecond pulses with phase masks enable pure two-beam interference generation due to order walk-off.