XUV frequency combs
Sources of XUV and soft X-ray radiation have normally been available only at large scale national facilities. Since the 1990s, low repetition rate (kHz), amplified femtosecond Ti:Sapphire laser systems have been employed to generate both EUV radiation and soft X-rays via high harmonic generation (HHG) in noble gases. While these table-top sources have found application in many scientific labs, a key shortcoming preventing their more widespread use and application is the low photon flux (or brightness). This condition is due in part to the extremely low inefficiency of the HHG conversion. In this project we are building on the pioneering initial work of R.J. Jones, J. Ye et al in which HHG was demonstrated within a phase-stabilized passive enhancement (buildup) cavity or femtosecond enhancement cavity (fsEC). This novel approach offers a route toward much higher photon flux along with production of XUV pulses out to 35 eV at 50-100 MHz in repetition rate and superior amplitude noise. All of these characteristics make this approach particularly attractive for use in XUV spectroscopy applications.
In our work we have optimized our fsEC-based XUV for photoemission spectroscopy with the latest iteration reported here.To seed the fsEC we employ an 60 MHz, 120 fs pulse train amplified to 20 W (post compression) using a Yb-doped fiber pre- and power- amplifier combination. Within the fsEC, an intra-cavity 200-nm pitch grating is used to simultaneously spectrally resolved and couple out the XUV pulse train. Currently we used Kryton as the target gas to reduced intra-cavity phase shifts from ionization and extend the XUV out to 35 eV. Here is a performance summary of our system optimized for photoemission spectroscopy:
- High resolution: ~25-30 meV)
- Broad photon energy coverage: 1-35 eV
- High photon flux: >10(^13) photons/second
- Temporal resolution: ~100 fs
- High repetition rate for fast data collection and low peak XUV power: > 50MHz
- click on photo to enlarge and for description -
