Abstract-Quantum correlation between optical and terahertz photons generated under multimode spontaneous parametric down-conversion

G. Kh. Kitaeva, A. A. Leontyev, and P. A. Prudkovskii

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.101.053810

We study conditions for the generation of strongly correlated photons of two extremely different frequency ranges, optical and terahertz, via the spontaneous parametric down-conversion effect in a nonlinear medium. Analytical expressions for the correlation function are derived using equations of the generalized Kirchhoff law for the second-order field moments with account of both classical thermal and quantum vacuum field fluctuations, possible inherent absorption of the medium at terahertz frequencies, and angular divergences of signal and idler radiation caused by a transverse limited spatial profile of the Gaussian pump beam. Associated with the current absence of terahertz photon counting detectors and coincidence schemes, the possible experimental limitations in measuring the second-order optical-terahertz field correlations are studied. Numerical calculations of noncollinear eee-geometry parametric down-conversion in a $\mathrm{Mg}:\mathrm{LiNb}{O}_3$ crystal demonstrate angular characteristics, particular features of the temperature and spectral behavior of the second-order quantum correlation function of optical-terahertz biphotons.

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Abstract-Electro-optic sampling of terahertz waves by laser pulses with an edge-cut spectrum in birefringent crystal

I. E. Ilyakov, G. Kh. Kitaeva, B. V. Shishkin, and R. A. Akhmedzhanov

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-9-1704

We demonstrate a terahertz detection technique based on variations of the energy of femtosecond laser pulses with an edge-cut spectrum in birefringent electro-optic crystal—periodically poled lithium niobate (PPLN). The method is compared with the standard electro-optic detection scheme utilizing GaP crystal. The experimental results show that the studied technique is suited for use with birefringent crystals and allows one to achieve a much better response to the terahertz wave radiation at quasi-phase-matching frequencies of PPLN.

© 2017 Optical Society of America

Abstract-Generation of optical-terahertz biphoton pairs via spontaneous parametric down-conversion

V. V. Kornienko

Corresponding author.

Faculty of Physics, Lomonosov Moscow State University, 1, Leninskiye Gory, GSP-1 Moscow 119991, Russia

S. A. Germanskiy

Faculty of Physics, Lomonosov Moscow State University, 1, Leninskiye Gory, GSP-1 Moscow 119991, Russia

G. Kh. Kitaeva

Faculty of Physics, Lomonosov Moscow State University, 1, Leninskiye Gory, GSP-1 Moscow 119991, Russia

A. N. Penin

Faculty of Physics, Lomonosov Moscow State University, 1, Leninskiye Gory, GSP-1 Moscow 119991, Russia

 http://www.worldscientific.com/doi/abs/10.1142/S0219749915600230?src=recsys&journalCode=ijqi


We examine the features of parametric down-conversion for generating non-classical optical-terahertz biphoton fields. The calculations were performed for a second-order correlation function and noise reduction factor (NRF), which were selected as measures of non-classicality of the field states. NRF measurement schemes were found to be less advantageous. Overall system temperature at which non-classical effects are still observable has been estimated as about 10 K. The priority of the main complicating factors for the quantum-optical measurements in the terahertz range has been determined. Thus, the most important parameter is the temperature of the system, after that come the absorption losses at terahertz frequencies, and the parametric conversion efficiency has the lowest impact. Increasing the pump radiation power has been found to be inefficient for "noise" suppression in this case. The calculations performed were based on lithium niobate dispersion properties due to its outstanding nonlinear optical properties and because it is frequently used for optical-to-terahertz frequency conversion.

Abstract-Absolute brightness measurements in the terahertz frequency range using vacuum and thermal fluctuations as references

My Note: This is slightly dated, but I wanted to include.

G. Kh. Kitaeva, 

P. V. Yakunin, 

V. V. Kornienko, 

A. N. Penin

http://link.springer.com/article/10.1007/s00340-014-5779-0

A total procedure for the terahertz wave brightness calibration using the quantum fluctuations at terahertz frequencies as a reference is formulated. An experimental proof for its theoretical background is provided. Klyshko method for the brightness calibration using spontaneous parametric down-conversion is modified, considering the case when the idler wave hits the terahertz frequency range and relative additives to the background signals induced by an external terahertz radiation can be measured both in Stokes and anti-Stokes ranges. It is shown at different temperatures that the thermal-fluctuation-induced signals have the same spectral and angular shapes, as the spontaneous parametric down-conversion signals, while the thermal-induced signal amplitudes are proportional to the number of photons in the thermal equilibrium modes

Abstract-Terahertz electro-optical detection: optical phase or energy measurements

 

S. P. Kovalev and G. Kh. Kitaeva  »View Author Affiliation
http://www.opticsinfobase.org/josab/abstract.cfm?URI=josab-30-10-2650

Models of different available single-photodetector electro-optic sampling schemes are considered from the unified theoretical position. It is taken into account that under electro-optic terahertz wave detection, not only do the polarization states of the femtosecond optical pulse components change but the modules of their amplitudes are also varied. As a result, information concerning the terahertz wave can be obtained not only using the conventional ellipsometry readout scheme (probe-phase sampling) but also by simple measuring of the induced power of the optical pulses (probe-energy sampling). Spectral sensitivities of both of these electro-optic sampling methods are calculated for the cases of nonlinear-optical crystals with zinc-blende symmetry (like ZnTe) and the crystals with one active component of the second-order optical susceptibility tensor (like PPLN). It is found that the ratio between spectral sensitivities of the pure probe-phase and pure probe-energy schemes is proportional to the ratio between the optical and terahertz wave frequencies in all types of the crystals. It is shown that the signal in the near-zero optical transmission point scheme, which is the best for terahertz imaging, has a mixed character. While the contribution of the probe-phase sensitivity appears to be due to spatially nonuniform residual birefringence of the nonlinear zinc-blende crystal, the probe-energy part of the sensitivity has a uniform distribution and can be increased by the angle misalignment of the optical polarization element.

© 2013 Optical Society of America