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How to Prevent Feedback and Damage in Ultrafast Fiber >797_word_end< using Coherent Optical Isolators
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Generating pulses below 10 picoseconds (ps) and into the femtosecond (fs) range, ultrafast laser systems can be designed for a range of operating regimes, depending upon target pulse energies and repetition rates. Two typical configurations are 1) an optical Master Oscillator Power Amplifier (>676_word_end<>702_word_end<) scheme for ps pulses and often with hybrid bulk-fiber design, and 2) a Chirped Pulse Amplifier (C>702_word_end<) scheme for fs pulses. Examples of these designs can be seen in Figures 1 and 2.
Practically speaking, whenever a laser system is designed using a mode-locked fiber oscillator as the pulse source, the oscillator typically provides only mW level output while system requirements can go to the 10s of Watts and beyond. >974_word_end< are required to achieve performance targets, and often use large-mode area (L>668_word_end<) amplifiers producing 1W to even up to more than 100W. But the oscillator can only remain stable with feedback on the microwatt (μW) level or less. Otherwise, noise that disturbs the spectral content can inhibit mode-locking or even cause Q-switching– the power that is fed back must be smaller than the ASE that pulses build from; this often means that an oscillator requires << 60 dB of feedback to remain stably mode-locked. In contrast, solid-state mode-locked oscillators can still operate with many times that amount of feedback. At the same time, if the seed pulse from the oscillator is interrupted at the input of an amplifier, Q-switching can result, which invariably leads to optical damage on a fiber end face.
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>2115_word_end< Typical >676_word_end<>702_word_end< Design, showing the use of isolators (denoted ISO) and their locations in the beam path.
>2131_word_end< Typical C>702_word_end< Design, showing the use of isolators (denoted ISO) and their locations in the beam path.
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See Figures 1 and 2 for examples of where to install isolators in >676_word_end<>702_word_end< and C>702_word_end< systems. An example of a real-world application can be found in reference 2>2144_word_end<.
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However, it is important to note that for pulses < 100 fs (pulses with broader bandwidth), the amount of dispersion will be greater - and this becomes an important consideration in many applications. As an example, in nonlinearly broadened systems, including certain C>702_word_end< systems, it is possible to produce < 100 fs pulses. If an isolator is required at the output of the laser system due to the possibility of feedback from the laser application, such as in material processing, this will add to the overall group velocity dispersion budget. In some cases, the effects of dispersion caused by the output isolator can be mitigated or removed by balancing it with dispersion in other parts of the system.
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By performing these c바카라사이트 추천culations, the amount of dispersion, β2, over the range of 1030 - 1080 nm was found to be ~ 1100 fs2 for 8 mm long TGG. The estimated broadening from that amount of second order dispersion for pulses in the range of 10 – 10,000 fs is shown in the graph below.
Figure 3: Broadening of a femtosecond pulse at ~ 1050 nm after propagation through 8 mm of TGG (blue curve); the red curve shows the output for undistorted pulses.
5 Conclusions
When designing ultrafast laser systems with fiber sub-systems, the use of protect>2169_word_end References: i Coherent User Manual for Faraday Rotators and Isolators >2144_word_end< J. Limpert, T. Schreiber, S. Nolte, H. Zellmer, and A. Tünnermann, "All fiber chirped-pulse amplification system based on compression in air-guiding photonic bandgap fiber," in Advanced Solid->624_word_end< Photonics (TOPS), G. Quarles, ed., Vol. 94 of OSA >2144_word_end2169_word_end >2169_word_end< As one source, see “Nonlinear Fiber >801_word_end<” by G. P. Agrawal for more details on group velocity dispersion v See the section on Dispers>2169_word_endContact us for more information on how to protect your ultrafast fiber 바카라사이트 추천 system from optical feedback.
Trends in >801_word_end< and Photonics (Optical Society of America, 2004), paper 9.