XUV Frequency Comb Metrology and the Ground State of Helium

Ubachs, W.M.G. [Promotor]Eikema, K.S.E. [Promotor

Phase stability of terawatt-class ultrabroadband parametric amplification

The phase stability of broadband (280 nm bandwidth) terawatt-class parametric amplification was measured, for the first time to our knowledge, with a combination of spatial and spectral interferometry. Measurements at four different wavelengths from 750 to 900 nm were performed in combination with numerical modeling. The phase stability is better than 1/23 rms of an optical cycle for all the measured wavelengths, depending on the phase-matching conditions in the amplifier. (C) 2007 Optical Society of America

Extreme ultraviolet frequency comb metrology

The remarkable precision of frequency-comb (FC) lasers is transferred to the extreme ultraviolet (XUV, wavelengths shorter than 100nm), a frequency region previously not accessible to these devices. A frequency comb at XUV wavelengths near 51nm is generated by amplification and coherent up-conversion of a pair of pulses originating from a near-infrared femtosecond FC laser. The phase coherence of the source in the XUV is demonstrated using helium atoms as a ruler and phase detector. Signals in the form of stable Ramsey-like fringes with high contrast are observed when the FC laser is scanned over P states of helium, from which the absolute transition frequency in the XUV can be extracted. This procedure yields a He4 ionization energy at h× 5945204212(6)MHz, improved by nearly an order of magnitude in accuracy, thus challenging QED calculations of this two-electron system. © 2010 The American Physical Society

Widely tunable extreme UV frequency comb generation

Extreme UV (XUV) frequency comb generation in the wavelength range of 51 to 85nm is reported based on highorder harmonic generation of two consecutive IR frequency comb pulses that were amplified in an optical parametric chirped pulse amplifier. The versatility of the system is demonstrated by recording direct XUV frequency comb excitation signals in He, Ne, and Ar with visibilities of up to 61%. © 2011 Optical Society of America

XUV frequency comb spectroscopy

Frequency comb lasers in the infrared region of the spectrum have revolutionized many fields of physics. We demonstrate for the first time direct frequency comb spectroscopy at XUV wavelengths. Generation of an XUV comb is realized by amplification of two pulses from a frequency comb laser in a parametric amplifier, and subsequent high-harmonic generation to 51 nm (15th harmonic). These XUV pulses, with a time separation between 5.4 and 10 ns, are then used to directly excite helium on the 1s2 1S0 – 1s5p 1P1 transition. The resulting Ramsey-like signal has up to 60% modulation contrast, indicating a high phase coherence of the generated XUV comb light