Satrapinski A.,Center for Metrology and Accreditation |
Novikov S.,Aalto University |
Lebedeva N.,Aalto University
Applied Physics Letters | Year: 2013
Precision quantum Hall resistance (QHR) measurements were performed on large-area epitaxial graphene device at temperature T = 1.5 K and at magnetic fields B from 8 T down to 2.5 T, that is much lower than typically used in precision QHR measurement. QHR was measured using cryogenic current comparator resistance bridge with relatively large biasing current Isd = 41 μA to reduce measurement uncertainty. The results showed that at B = 8 T, the relative deviation of Hall resistance from the expected quantized value h/2e2 is within experimental uncertainty of 3.5 parts in 10 8 and remained below 0.35 parts per million (ppm) down to B = 3 T. © 2013 AIP Publishing LLC.
Maisi V.F.,Aalto University |
Maisi V.F.,Center for Metrology and Accreditation |
Kambly D.,University of Geneva |
Flindt C.,University of Geneva |
Pekola J.P.,Aalto University
Physical Review Letters | Year: 2014
We employ a single-charge counting technique to measure the full counting statistics of Andreev events in which Cooper pairs are either produced from electrons that are reflected as holes at a superconductor-normal-metal interface or annihilated in the reverse process. The full counting statistics consists of quiet periods with no Andreev processes, interrupted by the tunneling of a single electron that triggers an avalanche of Andreev events giving rise to strongly super-Poissonian distributions. © 2014 American Physical Society.
Lassila A.,Center for Metrology and Accreditation
Measurement Science and Technology | Year: 2012
An instrument developed for high accuracy calibration of line scales up to 1.16m is described. The instrument is based on an earlier design from the early 1990s. Since then, in order to improve performance and achieve smaller uncertainty, large portions of software, mechanics and optics have been redesigned and several uncertainty components better characterized. The software has been developed to be less sensitive to imperfections of the line mark. In order to decrease noise and deformation coupling in interferometric measurement, the interferometer operating principle has been designed to use a fibre-coupled laser light, interferometer optics have been improved for better phase adjustment and detection and a differential interferometer principle has been taken into use. In order to minimize the effects due to deformations of the stone table rail with moving heavy carriage, a separate bed has been designed under line scale supports. The bed with fixed differential reflector prevents deformations of the table from affecting the line scale versus interferometer position. The main properties of the instrument are described and an uncertainty estimate is presented. The expanded uncertainty (k = 2) for line distance calibration of high-quality low-thermal-expansion line scale is U = [(4.5nm) 2 + (43×10 9L) 2] where L is the measured length. The results of international comparisons support the uncertainty estimate. © 2012 IOP Publishing Ltd.
Ulvila V.,University of Helsinki |
Phillips C.R.,ETH Zurich |
Halonen L.,University of Helsinki |
Vainio M.,University of Helsinki |
Vainio M.,Center for Metrology and Accreditation
Optics Letters | Year: 2013
We report optical frequency comb generation by a continuous-wave pumped optical parametric oscillator (OPO) without any active modulation. The OPO is configured as singly resonant with an additional nonlinear crystal (periodically poled MgO:LiNbO3) placed inside the OPO for phase mismatched second harmonic generation (SHG) of the resonating signal beam. The phase mismatched SHG causes cascading χ2 nonlinearities, which can substantially increase the effective χ3 nonlinearity in MgO:LiNbO3, leading to spectral broadening of the OPO signal beam via self-phase modulation. The OPO generates a stable 4 THz wide (-30 dB) frequency comb centered at 1.56 μm. © 2013 Optical Society of America.
Vainio M.,University of Helsinki |
Vainio M.,Center for Metrology and Accreditation |
Halonen L.,University of Helsinki
Optics Letters | Year: 2011
The frequency stability of a cw optical parametric oscillator (cw OPO) near the signal-idler degeneracy has been studied. The strong tendency of a near-degenerate OPO to mode hop has been suppressed by using a bulk Bragg grating as a spectral filter in the OPO cavity. An experimental demonstration of stable parametric oscillation in a single longitudinal mode of the OPO cavity is reported, together with the capability of tuning the signal-idler difference frequency from 1 to 4THz. The OPO has potential use in cw terahertz generation. © 2011 Optical Society of America.