Parametric Frequency Up-conversion Research Articles

Zeptojoule detection of terahertz pulses by parametric frequency upconversion.

We combine parametric frequency upconversion with the single-photon counting technology to achieve terahertz (THz) detection sensitivity down to the zeptojoule (zJ) pulse energy level. Our detection scheme employs a near-infrared ultrafast source, a GaP nonlinear crystal, optical filters, and a single-photon avalanche diode. This configuration is able to resolve 1.4 zJ (1.4 × 10-21 J) THz pulse energy, corresponding to 1.5 photons per pulse, when the signal is averaged within only 1 s (or 50,000 pulses). A single THz pulse can also be detected when its energy is above 1185 zJ. These numbers correspond to the noise-equivalent power and THz-to-NIR photon detection efficiency of 1.3 × 10-16 W/Hz1/2 and 5.8 × 10-2%, respectively. To test our scheme, we perform spectroscopy of the water vapor between 1 and 3.7 THz and obtain results that are in agreement with those acquired with a standard electro-optic sampling (EOS) method. Our technique provides a 0.2 THz spectral resolution offering a fast alternative to EOS THz detection for monitoring specific spectral components in spectroscopy, imaging, and communication applications.

Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO:LiNbO3 optical parametric amplifiers

Picosecond optical parametric generation and amplification in the near-infrared region within 1.361–1.656 μm and the mid-infrared region within 2.976–4.875 μm is constructed on the basis of bulk MgO:LiNbO3 crystals pumped at 1.064 μm. The maximum pulse energy reaches 1.3 mJ at 1.464 μm and 0.47 mJ at 3.894 μm, corresponding to a pump-to-idler photon conversion efficiency of 25%. By seeding the hard-to-measure mid-infrared radiation as the idler in the optical parametric amplification and measuring the amplified and frequency up-converted signal in the near-infrared or even visible region, one can measure very week mid-infrared radiation with ordinary detectors, which are insensitive to mid-infrared radiation, with a very high gain. A maximum gain factor of about 7 × 107 is achieved at the mid-infrared wavelength of 3.374 μm and the corresponding energy detection limit is as low as about 390 aJ per pulse.

Transient spectrometer for near-IR fluorescence based on parametric frequency upconversion

The authors report a unique technique for recording femtosecond time-resolved fluorescence spectra in the near IR by using idler-to-signal frequency upconversion in a 400nm pumped femtosecond noncollinear optical parametric amplifier, in which the IR fluorescence was seeded as the idler and the corresponding amplified signal branch is recorded. The spectra of the upconverted signal carry the information of the IR fluorescence and it were used in constructing the spectra of the IR dye. The transient fluorescence spectra from the upconverted signal reconstruct the spectra of the IR dye very well after deconvolution from the pump beam.

A theoretical study of operation conditions for a terahertz superlattice parametric oscillator

We report a theoretical study of operation conditions for a terahertz superlattice parametric oscillator (SPO). The SPO converts radiation of frequency ω to radiation at frequency 3 ω. The parametric process is based on the nonlinearity of the motion of a miniband electron in a high-frequency field consisting of a strong fundamental-frequency field and a higher harmonic field. In our study we made use of a semiclassical theory. Our analysis indicates that parametric frequency upconversion should allow for production of radiation up to several terahertz.

Nonlinear optical processes in planar waveguides and excitation of surface polaritons

An investigation is made of nonlinear optical interaction of light propagating in a planar waveguide with surface polaritons. Reduced wave equations for the amplitudes of the waveguide modes and surface polaritons are used to study the characteristics of generation of surface polaritons of difference frequency, parametric frequency up-conversion of the polaritons, and stimulated Raman scattering by the polaritons. An analysis is made of the characteristic properties of the investigated nonlinear optical processes.

Distortions of time characteristics in parametric up-conversion of ultrashort laser pulses

The dependence of the sum-frequency field on the fields of different frequencies mixed in a nonlinear medium is obtained for signals of 10−10–10−12 sec duration. The conditions are formulated for the smallness of distortions of the time characteristics of the investigated pulses and methods are proposed for restoring these characteristics in parametric frequency up-conversion.

Investigation of the statistical characteristics of spontaneous noise in parametric frequency converters

An experimental investigation was made of the statistical characteristics of spontaneous parametric luminescence generated in the course of parametric frequency up-conversion. It was found that the laws governing the amplitude distribution and the distribution of photocounts of parametric luminescence were nearly of the Poisson type.

Canonical Extension of a Problem in Parametric Frequency Up-conversion with Stochastic Pumping

A canonical model for the frequency up-conversion process with stochastic coupling function is proposed. Based on it the first-order coherence functions, the time dependence of the mean photon numbers and the second-order coherence functions are found and compared with the corresponding results already available in the literature. It is shown that the total photon number, as a function of time, has a turning point. The antibunching effect is predicted regardless of the mean photon numbers available in the process.

Detection of Room-Temperature Blackbody Radiation by Parametric Upconversion

Room-temperature thermal (blackbody) radiation has been detected via parametric-frequency upconversion. Thermal radiation was mixed with the output of a Nd:YAG laser in proustite. The wavelength of the radiation upconverted was varied from 6.5 to 12.5 μ by rotating the proustite 20 deg. The spectral width of the blackbody radiation accepted by the upconverter was approximately 0.7 μ.