Tunable Pump Research Articles

A tunable dual-wavelength pump source based on simulated polariton scattering for terahertz-wave generation

We propose a dual-wavelength pump source by utilizing stimulated polariton scattering in a LiNbO3 crystal. The residual pump and the generated tunable Stokes waves can be combined to generate THz-wave generation via difference frequency generation (DFG). With a pump energy of 49 mJ, Stokes waves with a tuning range from 1067.8 to 1074 nm have been generated, and an output energy of up to 14.9 mJ at 1070 nm has been achieved with a conversion efficiency of 21.7%. A sum frequency generation experiment was carried out to demonstrate the feasibility of the proposed scheme for THz-wave DFG.

Time‐lens based hyperspectral stimulated Raman scattering imaging and quantitative spectral analysis

We demonstrate a hyperspectral stimulated Raman scattering (SRS) microscope through spectral-transformed excitation. The 1064 nm Stokes pulse was from a synchronized time-lens source, generated through time-domain phase modulation of a continuous wave (CW) laser. The tunable pump pulse was from linear spectral filtering of a femtosecond laser output with an intra-pulse spectral scanning pulse shaper. By electronically modulating the time-lens source at 2.29 MHz, hyperspectral stimulated Raman loss (SRL) images were obtained on a laser-scanning microscope. Using this microscope, DMSO in aqueous solution with a concentration down to 28 mM could be detected at 2 μs time constant. Hyperspectral SRL images of prostate cancer cells were obtained. Multivariate curve resolution analysis was further applied to decompose the SRL images into concentration maps of CH₂ and CH₃ bonds. This method offers exciting potential in label-free imaging of live cells using fingerprint Raman bands.

Enhanced Second Harmonic Generation by Photonic–Plasmonic Fano-Type Coupling in Nanoplasmonic Arrays

In this communication, we systematically investigate the effects of Fano-type coupling between long-range photonic resonances and localized surface plasmons on the second harmonic generation from periodic arrays of Au nanoparticles arranged in monomer and dimer geometries. Specifically, by scanning the wavelength of an ultrafast tunable pump laser over a large range, we measure the second harmonic excitation spectra of these arrays and demonstrate their tunability with particle size and separation. Moreover, through a comparison with linear optical transmission spectra, which feature asymmetric Fano-type lineshapes, we demonstrate that the second harmonic generation is enhanced when coupled photonic-plasmonic resonances of the arrays are excited at the fundamental pump wavelength, thus boosting the intensity of the electromagnetic near-fields. Our experimental results, which are supported by numerical simulations of linear optical transmission and near-field enhancement spectra based on the Finite Difference Time Domain method, demonstrate a direct correlation between the onset of Fano-type coupling and the enhancement of second harmonic generation in arrays of Au nanoparticles. Our findings enable the engineering of the nonlinear optical response of Fano-type coupled nanoparticle arrays that are relevant to a number of device applications in nonlinear nano-optics and plasmonics, such as on-chip frequency generators, modulators, switchers, and sensors.

Gigahertz quantized charge pumping in graphene quantum dots

Single-electron pumps are set to revolutionize electrical metrology by enabling the ampere to be redefined in terms of the elementary charge of an electron. Pumps based on lithographically fixed tunnel barriers in mesoscopic metallic systems and normal/superconducting hybrid turnstiles can reach very small error rates, but only at megahertz pumping speeds that correspond to small currents of the order of picoamperes. Tunable barrier pumps in semiconductor structures are operated at gigahertz frequencies, but the theoretical treatment of the error rate is more complex and only approximate predictions are available. Here, we present a monolithic, fixed-barrier single-electron pump made entirely from graphene that performs at frequencies up to several gigahertz. Combined with the record-high accuracy of the quantum Hall effect and proximity-induced Josephson junctions, quantized-current generation brings an all-graphene closure of the quantum metrological triangle within reach. Envisaged applications for graphene charge pumps outside quantum metrology include single-photon generation via electron-hole recombination in electrostatically doped bilayer graphene reservoirs, single Dirac fermion emission in relativistic electron quantum optics and read-out of spin-based graphene qubits in quantum information processing.

Multi-wavelength generation by self-seeded four-wave mixing

A cost effective method of generating multi-wavelength based on the cascaded four wave mixing effect is experimentally demonstrated. The proposed scheme is free from external tunable laser sources and pump modulators, resulting from the use of a broadened linewidth tunable dual wavelength erbium-doped fiber laser as intracavity pump. In this configuration, the number of four wave mixing cascades becomes larger in tandem with the increment of erbium-doped fiber amplifier output power. When its output power is set at 20.57 dBm, six waves having optical signal to noise ratio larger than 10 dB are generated. The six waves are stable with peak power fluctuations less than 1 dB within 30 minutes period and tunable with wavelength spacing ranging from 1.03 nm to 11.31 nm.

All-Optically Controlled Quantum Memory for Light with a Cavity-Optomechanical System

Optomechanics may be viewed as a light-mechanics interface to realize hybrid structures for (classical or quantum) information processing, switching or storage. Using the two-laser technique, in this paper, we theoretically devise a protocol for quantum light memory via a cavity optomechanical system composed of a Fabry–Perot cavity and a mechanical resonator. Due to the long-lived mechanical resonator, this quantum memory for light based on optomechanically induced transparency (OMIT) can serve as a long-term memory that can store the full quantum light contained in an optical pulse. It is shown that, with the tunable pump laser, the quantum signal light can be reaccelerated and converted back on demand. Our presented work could open the door to all-optical routers for light memory devices and have a guide to actual experiments.

Automation of an “Aculight” continuous-wave optical parametric oscillator

We report the automation of a continuous-wave, singly resonant, optical parametric oscillator (Lockheed-Martin Aculight ARGOS 2400-SF-15). This commercially available optical parametric oscillator (OPO) is capable of producing >1 W of continuously tunable idler output between 2.2 and 4.6 μm. An algorithm based on the feedback from a high accuracy wavemeter is implemented to synchronize three separate OPO tuning elements; the translation of a fan-out type periodically poled lithium niobate crystal, the rotation of an intracavity etalon, and the continuous tuning of the pump and idler wavelengths via piezoelectric strain of the tunable fiber pump laser. This allows for several hundred wavenumbers of efficient, automatic, continuous tuning of the idler wave. Continuous feedback from the wavemeter limits the absolute frequency accuracy to ±20 MHz. The broad, automatic tuning of the OPO is demonstrated via its implementation as a probe laser for the infrared action spectroscopy of methanol solvated in helium nanodroplets. LabVIEW virtual instruments for the automation of this OPO laser system are reported, along with detailed schematics of the associated hardware developed at the University of Georgia.

Dark excited states of carotenoid in light harvesting complex probing with femtosecond stimulated Raman spectroscopy

Vibrational dynamics of dark excited states in carotenoids have been investigated using tunable Raman pump pulses. The S1 state has same vibrational dynamics in light-harvesting complex (LH1) and solution. The S* state in LH1 has similar vibrational modes with the triplet state of carotenoid. However, the so-called S* state in solution does not have the modes and is concluded to be different from the S* state in LH1.

Recent Patents on Raman Amplifiers

With the increasing requirement of communication rate and capacity, Raman amplifiers are becoming the most promising technologies in optical communication systems. There are many patents about Raman amplifiers. In this paper, some important inventions in the patents about Raman amplifiers published since the last 3 years will be presented as typical examples. This paper will introduce various types of inventions about Raman amplifiers individually: multipleorder Raman amplifiers, tunable multimode pump sources Raman amplifiers, automatic gain control Raman amplifiers and lumped Raman amplifiers with a highly-nonlinear medium. These inventions are classified from the principle of Raman amplification effect, the implementation way, deployment mode and optical materials and devices to realize innovation. Above all, Raman amplifiers are developing towards greater capacity, lower noise and nonlinearity, higher gain and longer fiber span lengths. Keywords: Raman amplifiers, optical transmission, multiple-order, tunable, gain control, optical materials and devices, Amplifiers, amplification, first-order Stokes pumping, first pump source

Broadly tunable mode-hop-free mid-infrared light source with MgO:PPLN continuous-wave optical parametric oscillator

We report a continuous-wave, broadly tunable mid-infrared MgO:PPLN optical parametric oscillator pumped by a fiber amplifier. Using pump tuning with synchronized temperature optimization, we achieve the broadest mode-hop-free (MHF) tuning of idler light over 30 cm(-1). We further use this tunable mid-infrared laser to demonstrate high-resolution absorption spectroscopy of methane across the MHF tuning range.

Experimental determination of the Boltzmann constant: An undergraduate laboratory exercise for molecular physics or physical chemistry

This article describes an undergraduate laboratory exercise that uses optical spectroscopy to determine the magnitude and the uncertainty of the Boltzmann constant kb. The more accurate approach uses photoacoustic spectroscopy to measure the Doppler-broadened line profile of individual spectral lines of N2O to extract kb. Measurements and estimates of the uncertainties in the quantities needed to calculate kb from the line profiles are then used to estimate the uncertainty in kb. This experiment is unusual in that it uses advanced laser-based spectroscopy techniques to emphasize standard practices of uncertainty analysis. The core instrumentation is modular and relatively affordable; it requires a tunable single-mode laser, photoreceiver, optical cell, and vacuum pump. If this instrumentation is not available, an alternate approach can be performed which uses the intensity of each rotational transition of an infrared band to measure kb. Although there is more uncertainty using the alternate approach, low concentrations of CO2, DCl, or N2O give reasonable results for the magnitude of kb. Student assessment results indicate retention and mastery of the concept of combined measurement uncertainty.

Quantum-Dash Mode-Locked Lasers for Tunable Wavelength Conversion on a 100 GHz Frequency Grid

All-optical wavelength converters play a key role for next-generation high-bit-rate optical networks. A high-speed, simple, and compact wavelength converter can resolve contention, reduce wavelength blocking, and enable a multitude of new wavelength routing approaches. We propose the combination of a quantum-dash mode-locked laser (QD-MLL) with a frequency-selective filter to provide (two) tunable wavelength pumps for wavelength conversion of optical channels in a dual-pump four-wave-mixing (FWM) scheme. Such a converter is simple, practical, and offers a wide conversion range, modulation format transparency, and the potential for photonic integration. We examine the performance of the proposed scheme experimentally with a QD-MLL and manually tunable optical filters. Wavelength conversion is achieved via an extremely non-linear semiconductor optical amplifier (SOA), a commercial SOA with very high FWM efficiency. We achieved near −3 dB conversion efficiency across a 9.6 nm tuning range with a signal input power of −3 dBm and a pump input power of 2 dBm. We performed bit error rate (BER) measurement on a 5.6 nm conversion range and obtained error-free transmission (BER <10−9) with less than 2 dB power penalty.

Spectral linewidth preservation in parametric frequency combs seeded by dual pumps

We demonstrate new technique for generation of programmable-pitch, wideband frequency combs with low phase noise. The comb generation was achieved using cavity-less, multistage mixer driven by two tunable continuous-wave pump seeds. The approach relies on phase-correlated continuous-wave pumps in order to cancel spectral linewidth broadening inherent to parametric comb generation. Parametric combs with over 200-nm bandwidth were obtained and characterized with respect to phase noise scaling to demonstrate linewidth preservation over 100 generated tones.

Enhancement of spectral resolution and optical rejection ratio of Brillouin optical spectral analysis using polarization pulling

High-resolution, wide-bandwidth optical spectrum analysis is essential to the measuring and monitoring of advanced optical, millimeter-wave, and terahertz communication systems, sensing applications and device characterization. One category of high-resolution spectrum analyzers reconstructs the power spectral density of a signal under test by scanning a Brillouin gain line across its spectral extent. In this work, we enhance both the resolution and the optical rejection ratio of such Brillouin-based spectrometers using a combination of two techniques. First, two Brillouin loss lines are superimposed upon a central Brillouin gain to reduce its bandwidth. Second, the vector attributes of stimulated Brillouin scattering amplification in standard, weakly birefringent fibers are used to change the signal state of polarization, and a judiciously aligned output polarizer discriminates between amplified and un-amplified spectral contents. A frequency resolution of 3 MHz, or eight orders of magnitude below the central optical frequency, is experimentally demonstrated. In addition, a weak spectral component is resolved in the presence of a strong adjacent signal, which is 30 dB stronger and detuned by only 60 MHz. The measurement method involves low-bandwidth direct detection, and does not require heterodyne beating. The measurement range of the proposed method is scalable to cover the C + L bands, depending on the tunable pump source. The accuracy of the measurements requires that the pump frequencies are well calibrated.

Ultrabroadband femtosecond two-dimensional ultraviolet transient absorption

We present a broadband two-dimensional transient absorption setup for the UV around 300 nm with a time resolution of 150 fs. A narrowband, frequency tunable pump pulse and a broadband probe pulse are generated from the output of a noncollinear optical parametric amplifier operated at 20 kHz repetition rate and combined in a spectrally resolved transient absorption experiment. The high repetition rate and low noise of the setup allow us to acquire high quality two-dimensional data as a function of time delay with an unsurpassed frequency window of 10,000 and 8000 cm(-1) along the probe and pump axis, respectively. The performance of the setup is demonstrated on 2,5-Diphenyloxazol dissolved in cyclohexane.

Fiber delivered two-color picosecond source through nonlinear spectral transformation for coherent Raman scattering imaging

We demonstrate a two-color, fiber-delivered picosecond source for coherent Raman scattering (CRS) imaging through nonlinear spectral transformation. The wavelength tunable picosecond pump is generated by nonlinear spectral compression of a prechirped femtosecond pulse in a fiber wavelength division multiplexer (WDM). The 1064-nm synchronized picosecond Stokes pulse is generated through pulse carving of a continuous wave laser, nonlinear spectral broadening in 100-m standard single-mode fiber, and subsequent dispersive compression with a fiber compressor. The pump and Stokes beams are combined and delivered by the fiber WDM. CRS imaging of mouse skin is performed to demonstrate the practicality of this source.

Tracking energy transfer between light harvesting complex 2 and 1 in photosynthetic membranes grown under high and low illumination

Energy transfer (ET) between B850 and B875 molecules in light harvesting complexes LH2 and LH1/RC (reaction center) complexes has been investigated in membranes of Rhodopseudomonas palustris grown under high- and low-light conditions. In these bacteria, illumination intensity during growth strongly affects the type of LH2 complexes synthesized, their optical spectra, and their amount of energetic disorder. We used a specially built femtosecond spectrometer, combining tunable narrowband pump with broadband white-light probe pulses, together with an analytical method based on derivative spectroscopy for disentangling the congested transient absorption spectra of LH1 and LH2 complexes. This procedure allows real-time tracking of the forward (LH2→LH1) and backward (LH2←LH1) ET processes and unambiguous determination of the corresponding rate constants. In low-light grown samples, we measured lower ET rates in both directions with respect to high-light ones, which is explained by reduced spectral overlap between B850 and B875 due to partial redistribution of oscillator strength into a higher energetic exciton transition. We find that the low-light adaptation in R. palustris leads to a reduced elementary backward ET rate, in accordance with the low probability of two simultaneous excitations reaching the same LH1/RC complex under weak illumination. Our study suggests that backward ET is not just an inevitable consequence of vectorial ET with small energetic offsets, but is in fact actively managed by photosynthetic bacteria.

Broadband Brillouin slow light with multiple-longitudinal-mode, tunable pump

We propose and demonstrate broadband Brillouin slow light using a multiple-longitudinal-mode tunable fiber laser as Brillouin pump. A tunable broadband Brillouin pump with a tuning range from 1 520 to 1 555 nm is generated using a fiber ring laser with a semiconductor optical amplifier (SOA) as its gain medium. The pump spectrum consists of a large number of longitudinal modes separated by 6 MHz. The 3-dB bandwidth is about 11.5 GHz, and its fluctuation is less than 100 MHz within the tuning range. An 8-Gb/s data signal can be delayed by up to 83.0 ps (bit error rate < 10?9) at 17-dBm pump power.

Angle-resolved and internuclear-separation-resolved measurements of the ionization rate of theBstate of I2by strong laser fields

Angle-resolved and internuclear-separation-resolved measurements of the single ionization rate of neutral I${}_{2}$ have been obtained. By launching a wave packet in the $B{\phantom{\rule{0.16em}{0ex}}}^{3}\ensuremath{\Pi}{{}_{u}}^{+}$ state ($B$ state) of I${}_{2}$ with a 50-fs tunable pump pulse we can measure the ionization rate as a function of internuclear separation as the wave packet evolves in the $B$ state. Moreover, since the ground to $B$-state optical transition dipole moment is parallel to the internuclear axis, the $B$-state subpopulation of the I${}_{2}$ thermal ensemble will have a high degree of alignment, allowing for angular measurements. The $B$ state shows the well-known effect of enhanced ionization at a critical separation, $R$${}_{c}$, with an enhancement factor of 22 when the ionizing field is polarized along the internuclear axis and the enhanced ionization decreases when the angle between the field and the axis increases from 0 ${}^{\ensuremath{\circ}}$ to 90 ${}^{\ensuremath{\circ}}$, finally disappearing at 90 ${}^{\ensuremath{\circ}}$. These results on the enhanced ionization of the $B$ state of I${}_{2}$ give the most precise determination of $R$${}_{c}$ for any molecule and agree extremely well with the prediction from a simple model of electron localization.

Multistability of a two-component exciton-polariton fluid

We study the stability of a multicomponent exciton-polariton fluid under resonant excitation within the linear response approximation of a generalized Gross-Pitaevskii equation. We show that, two spatially homogeneous and independently tunable pumping lasers produce, for the same values of the system parameters, up to three stable solutions. Three-stability is understood by noting that the cavity can be either little or highly populated and, in this second case, the largest part of the population lies in either one of the two components. Moreover, we show that easily tunable multistable hysteresis loops can be performed by the system.