2015 BFY II Abstract Detail Page
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||W15 - An erbium-doped femtosecond fiber laser for the undergraduate laboratory
||The fields of ultrafast optics, mode-locked fiber lasers, and frequency combs are mature yet continue to find new and interdisciplinary applications. Although such apparatus are perhaps somewhat uncommon in the undergraduate optics lab, the concepts and required skills are used in state-of-the-art physics, engineering and industrial settings. This workshop will describe an ultrafast optics laboratory comprising a mode-locked erbium fiber laser centered at approximately 1550 nm, auto-correlation measurements, and a free-space parallel grating dispersion compensation apparatus. The stretched pulse laser uses nonlinear polarization rotation mode-locking to produce pulses as narrow as 108 fs, full-width at half-maximum, at a repetition rate of 55 MHz and average power of 5.5 mW from the laser oscillator. A pre-amplifier following the oscillator increases average power to 21~mW. Interferometric and intensity auto-correlation measurements are made using a Michelson interferometer that takes advantage of the two-photon nonlinear response of a common silicon photodiode for the second order correlation between pulses. A parallel grating dispersion compensation apparatus decreases chirp and increases peak intensity, narrowing the pulse width by a factor of 13.
The laboratory was developed in the context of two upper-level undergraduate physics courses: Optics and Lasers. Participants will view a video and computer presentation describing the relevant physics, construction and operation of the laser and apparatus. They will receive a detailed parts list that includes previously owned and common parts used by the telecommunications industry, which may decrease the cost of the lab to within reach of many undergraduate departments. The mode-locked laser system can be built for less than 7000 USD, which is dominated by the fiber fusion splicer. The auto-correlation apparatus can be built for approximately 2200 USD, which includes precision gold corner cube retroreflectors. The parallel grating pulse compression apparatus can be built for less than 1200 USD, which includes high efficiency transmission gratings.
This workshop will present two promising methods to further reduce the cost of the lab. Lasers course project groups are currently developing a connectorized version of the mode-locked laser oscillator, and an IR scanning monochromator based on a small stepper motor controlled by an Arduino microcontroller. The former would circumvent the need for a fiber fusion splicer (~2500 USD, used). The monochromator could be used to characterize the pulse spectrum. Along with the descriptive video, presentation, documentation of results and parts list, participants will have the opportunity to inspect various laser components.
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|Workshop Doc 2:
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