Nonlinear Down-conversion Research Articles

Nonlinear down-conversion in a single quantum dot

Tailored nanoscale quantum light sources, matching the specific needs of use cases, are crucial building blocks for photonic quantum technologies. Several different approaches to realize solid-state quantum emitters with high performance have been pursued and different concepts for energy tuning have been established. However, the properties of the emitted photons are always defined by the individual quantum emitter and can therefore not be controlled with full flexibility. Here we introduce an all-optical nonlinear method to tailor and control the single photon emission. We demonstrate a laser-controlled down-conversion process from an excited state of a semiconductor quantum three-level system. Based on this concept, we realize energy tuning and polarization control of the single photon emission with a control-laser field. Our results mark an important step towards tailored single photon emission from a photonic quantum system based on quantum optical principles.

Progress on intra-pulse difference frequency generation in femtosecond laser

Mid-infrared (MIR) lasers have various advantages and can be widely used in either fundamental research fields or practical applications such as strong-field physics, molecular sensing and minimally-invasive tissue ablation. Generally, there are two categories of methods to generate MIR laser emission: one is direct lasing and the other is nonlinear frequency down-conversion. However, for the ultra-broadband few-cycle MIR generation, nonlinear down-conversion is the only available method. Intra-pulse Difference Frequency Generation (IP-DFG) is a simple method of nonlinear frequency conversion. In this article, the IP-DFG technology for the ultra-broadband MIR few-cycle pulses generation is reviewed. Different MIR nonlinear crystals, various driving laser sources, the spectral coverage of the MIR-IPDF output, and the conversion efficiency are compared and discussed. Last but not least, the prospects and challenges of MIR IP-DFG are presented.

Potential of Sub-THz-Wave Generation in Li2B4O7 Nonlinear Crystal at Room and Cryogenic Temperatures

Due to their high optical damage threshold, borate crystals can be used for the efficient nonlinear down-conversion of terawatt laser radiation into the terahertz (THz) frequency range of the electromagnetic spectrum. In this work, we carried out a thorough study of the terahertz optical properties of the lithium tetraborate crystal (Li2B4O7; LB4) at 295 and 77 K. Approximating the terahertz refractive index in the form of Sellmeier’s equations, we assessed the possibility of converting the radiation of widespread high-power laser sources with wavelengths of 1064 and 800 nm, as well as their second and third harmonics, into the THz range. It was found that four out of eight types of three-wave mixing processes are possible. The conditions for collinear phase matching were fulfilled only for the o − e → o type of interaction, while cooling the crystal to 77 K did not practically affect the phase-matching curves. However, a noticeable increase of birefringence in the THz range with cooling (from 0.12 to 0.16) led to an increase in the coherence length for o − o → e and e − e → e types of interaction, which are potentially attractive for the down-conversion of ultrashort laser pulses.

Nonlinear frequency down-conversion of acoustic wave beams in the atmosphere and ionosphere under different types of modulation (regular item)

It is investigated theoretically the nonlinear down-conversion of powerful extremely low frequency (ELF) modulated acoustic wave beams at the carrier frequencies 1–20 Hz into ultra-low frequency (ULF) acoustic waves at the frequencies 0.01–0.1 Hz under the propagation upwards within the atmosphere and ionosphere. The approximation of the slowly varying profile is used. It is shown that under a fixed value of the integral power of the initial acoustic ELF beam there exists the optimal value of the initial transverse width where the maximum down-conversion is realized. The different types of the modulation are considered, namely the simplest two-frequency modulation and multifrequency noise-like one. The using of the complex multifrequency modulation results in the increase of the efficiency of the down-conversion within the ionosphere E- and F-layers.

24 mJ Cr+4:forsterite four-stage master-oscillator power-amplifier laser system for high resolution mid-infrared spectroscopy.

We present the design of a Cr:forsterite based single-frequency master-oscillator power-amplifier laser system delivering much higher output energy compared to previous literature reports. The system has four amplifying stages with two-pass configuration each, thus enabling the generation of 24 mJ output energy in the spectral region around 1262 nm. It is demonstrated that the presented Cr:forsterite amplifier preserves high spectral and pulse quality, allowing a straightforward energy scaling. This laser system is a promising tool for tunable nonlinear down-conversion to the mid-infrared spectral range and will be a key building block in a system for high-resolution muonic hydrogen spectroscopy in the 6.8 μm range.

Parametric effects in circuit quantum electrodynamics

We review recent advances in the research on quantum parametric phenomena in superconducting circuits with Josephson junctions. We discuss physical processes in parametrically driven tunable cavity and outline theoretical foundations for their description. Amplification and frequency conversion are discussed in detail for degenerate and nondegenerate parametric resonance, including quantum noise squeezing and photon entanglement. Experimental advances in this area played decisive role in successful development of quantum limited parametric amplifiers for superconducting quantum information technology. We also discuss nonlinear down-conversion processes and experiments on self-sustained parametric and subharmonic oscillations.

Influence of pump coherence on the generation of position-momentum entanglement in optical parametric down-conversion.

We examine experimentally how the degree of position-momentum entanglement of photon pairs depends on the transverse coherence of the pump beam that excites them in a process of spontaneous parametric down-conversion. Using spatially incoherent light from a light-emitting diode, we obtain strong position correlation of the photons, but we find that transverse momentum correlation, and thus entanglement, is entirely absent. When we continuously vary the degree of spatial coherence on the pump beam, we observe the emergence of stronger momentum correlations and entanglement. We present theoretical arguments that explain our experimental results. Our results shed light on entanglement generation and can be applied to control entanglement for quantum information applications.

Integrated Nonlinear Waveguide Optics for High-Efficiency and Wideband-Tunable Generation of THz Radiation

On the basis of nonlinear downconversion, we propose how folded waveguide structures can be utilized as highly efficient, compact, and tunable sources of THz radiation. A folded waveguide arrangement allows us to exploit long-range efficient light–matter interaction at a compact geometrical footprint. Nonlinear THz generation in these systems is analytically modeled with results well supported by numerical simulations. For a practical device, based on the silicon photonics platform in combination with nonlinear organic materials, we show that the emitted THz radiation has a monochromatic continuous wave power on the order of tens of microwatts. The required optical input power is only 100 milliwatts. The THz emission frequency can be in situ tuned to any desired frequency in the 1–10 THz spectral range without spectral gaps. This unique property makes such integrated THz sources suitable for applications in THz spectroscopy and THz imaging.

Quantum nonlinear light emission in metamaterials: broadband Purcell enhancement of parametric downconversion

Single-photon and correlated two-photon sources are important elements for optical information systems. Nonlinear downconversion light sources are robust and stable emitters of single photons and entangled photon pairs. However, the rate of downconverted light emission, dictated by the properties of low-symmetry nonlinear crystals, is typically very small, leading to significant constraints in device design and integration. In this Letter, we study principles of spontaneous emission control (i.e., the Purcell effect) generalized to describe the enhancement of nonlinear generation of quantum light through spontaneous parametric downconversion. We develop a theoretical framework based on eigenmode analysis to study quantum nonlinear emission in a general anisotropic, dispersive, and lossy media. Our theory provides an unprecedented insight into the emission process. We find that spontaneous parametric downconversion in a media with hyperbolic dispersion is broadband and phase-mismatch-free. We further predict a significant enhancement of the downconverted emission rate in experimentally realistic nanostructures. Our theoretical formalism and approach to Purcell enhancement of nonlinear optical processes provides a framework for description of quantum nonlinear optical phenomena in complex nanophotonic structures.

Proposal for Quantum Simulation via All-Optically-Generated Tensor Network States.

We devise an all-optical scheme for the generation of entangled multimode photonic states encoded in temporal modes of light. The scheme employs a nonlinear down-conversion process in an optical loop to generate one- and higher-dimensional tensor network states of light. We illustrate the principle with the generation of two different classes of entangled tensor network states and report on a variational algorithm to simulate the ground-state physics of many-body systems. We demonstrate that state-of-the-art optical devices are capable of determining the ground-state properties of the spin-1/2 Heisenberg model. Finally, implementations of the scheme are demonstrated to be robust against realistic losses and mode mismatch.

Frequency-comb-assisted precision laser spectroscopy of CHF3 around 8.6 μm.

We report a high-precision spectroscopic study of room-temperature trifluoromethane around 8.6 μm, using a CW quantum cascade laser phase-locked to a mid-infrared optical frequency comb. This latter is generated by a nonlinear down-conversion process starting from a dual-branch Er:fiber laser and is stabilized against a GPS-disciplined rubidium clock. By tuning the comb repetition frequency, several transitions falling in the υ5 vibrational band are recorded with a frequency resolution of 20 kHz. Due to the very dense spectra, a special multiple-line fitting code, involving a Voigt profile, is developed for data analysis. The combination of the adopted experimental approach and survey procedure leads to fractional accuracy levels in the determination of line center frequencies, down to 2 × 10(-10). Line intensity factors, pressure broadening, and shifting parameters are also provided.

Mid-infrared frequency comb for broadband high precision and sensitivity molecular spectroscopy.

We report on the experimental demonstration of the metrological and spectroscopic performances of a mid-infrared comb generated by a nonlinear downconversion process from a Ti:sapphire-based near-infrared comb. A quantum cascade laser at 4330 nm was phase-locked to a single tooth of this mid-infrared comb and its frequency-noise power spectral density was measured. The mid-infrared comb itself was also used as a multifrequency highly coherent source to perform ambient air direct comb spectroscopy with the Vernier technique, by demultiplexing it with a high-finesse Fabry-Perot cavity.

Narrow linewidth single-frequency terahertz source based on difference frequency generation of vertical-external-cavity source-emitting lasers in an external resonance cavity

We demonstrate a continuous wave, single-frequency terahertz (THz) source emitting 1.9THz. The linewidth is less than 100kHz and the generated THz output power exceeds 100μW. The THz source is based on parametric difference frequency generation within a nonlinear crystal located in an optical enhancement cavity. Two single-frequency vertical-external-cavity source-emitting lasers with emission wavelengths spaced by 6.8nm are phase locked to the external cavity and provide pump photons for the nonlinear downconversion. It is demonstrated that the THz source can be used as a local oscillator to drive a receiver used in astronomy applications.

Time‐resolved photoluminescence studies of high‐brightness 340‐nm LEDs under current injection

AbstractWe present time‐resolved photoluminescence studies on high‐brightness, 340‐nm LEDs under current injection. Devices exhibiting >5 mW at 100 mA drive current from a 100 µm × 100 µm area have been fabricated. PL lifetime measurements of InAlGaN multiple quantum well active regions under current injection are correlated with device operating parameters by using a nonlinear downconversion, optical‐gating technique. In wafer level measurements, a decrease in PL lifetime by ∼17% from 410 to 340ps as the injection current is increased from turn‐on to the onset of roll‐over (∼150 mA) may be at tributed to enhanced nonradiative recombination associated with device heating. An increase in the low‐current PL lifetime relative to that measured in the unbiased device is representative of trap saturation and screening of the MQW electric field through current injection prior to device heating. In addition, the PL lifetime was found to vary little over an operating time of ∼1900 hours, despite the drop in EL power by ∼50 percent. This result suggests that the degradation of the active region is not the major cause of the decrease in device performance over time. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spatio-temporal instabilities and threshold condition in a broad-area optical parametric oscillator

The role of diffraction on the threshold condition for signal generation in a broad-area, doubly-resonant optical parametric oscillator (OPO) operating close to degeneracy is analytically investigated starting from a three-dimensional model of the OPO equations. The instability domain for signal generation, as derived in terms of general cavity parameters, is shown to be composed by two families of multiballoon (or multiconical) regions, which correspond to the two discrete sets of longitudinal modes for the OPO. Depending on the cavity detuning parameter, parametric oscillation is preferred to occur on either one of the two mode families, and may be associated to an off-axis emission. Due to the conservation of the photon momentum in the nonlinear down-conversion process, a discrimination among the different instability balloons exists, which explains the asymmetric behavior of threshold curves versus cavity length tuning and makes unlikely the occurrence of multiconical emission in the OPO.