An efficient femtosecond pulse amplification technique for extracting the maximum stored energy in fiber laser amplifiers

The well-known journal Optica published a paper in November 2024 titled "Near complete extraction of maximum stored energy from large core fibers using coherent pulse stacking amplification of femtosecond pulses"The authors of the paper were the University of Michigan, Lawrence Berkeley National Laboratory, Peking University, and the German Institute of Synchrotron Radiation.

The specific technique is to use a cascaded "GTI" (Gire Tounois interferometer) method to synthesize 81 amplified pulses together in the time domain. The technical difficulty that needs to be overcome is to control the phase and amplitude of each pulse to achieve coherent synthesis. The core femtosecond light source is a 1 GHz repetition rate femtosecond fiber laser, developed by Professor Zhang Zhigang's group at the School of Electronics, Peking University.

The author of the paper has demonstrated using the aforementioned techniques that, with a continuous pump of 100 W and a repetition rate of 2 kHz, nearly 10 mJ of amplified pulse energy can be extracted, far exceeding the energy output of conventional large mode area fiber amplifiers, which can reach less than 1 mJ. The extraction efficiency is close to 90%.

This efficient time-domain pulse synthesis technique can greatly improve the efficiency of pulse synthesis and reduce the number of amplifiers used for spatial synthesis.

Although the repetition rate and pulse energy obtained from this experiment are not yet high, this technology demonstrates the potential to generate femtosecond strong laser pulses with Joule level pulse energy and repetition rates above 10 kHz. It may provide a light source for studying strong field physics and particle accelerators under extreme conditions, as well as for generating secondary radiation.

Figure 1 shows the efficiency of pulse energy extraction in a fiber amplifier independent of core diameter under nonlinear confinement. Figure 1 indicates that the pulse extraction efficiency can only approach 100% of the amplifier's stored energy when the pulse is broadened to 100 ns

Figure 2 shows a schematic diagram of a composite GTI cavity, where 81 incident laser pulses are coherently superimposed in four large loop cavities to form 9 pulses; Then coherently superimpose them into one pulse in four small cavities

Figure 3: Photo of the Composite GTI Chamber Experimental Device

Figure 4 shows the pulse waveform and spectrum of the coherent synthesized pulse with an energy of 3 mJ and a width of 313 fs

Source: Yangtze River Delta Laser Alliance