Difference Frequency Mixing Research Articles

Terahertz generation by difference-frequency mixing of exciton Wannier–Stark ladder states in biased semiconductor superlattices

We report the generation of terahertz (THz) radiation in a biased semiconductor superlattice by difference-frequency mixing of interband transitions. The Wannier–Stark spectrum of the superlattice was selectively excited by two spectrally narrow laser lines. The emitted THz radiation was measured as a function of the energetic splitting and spectral position of the bichromatic excitation. The generation of tunable THz radiation is verified. The results clearly show enhanced THz emission when either continuum or 1s exciton wave packets are excited. Good agreement is obtained between the experiment and the results of an exciton model of the nonlinear coherent dynamics.

Tunable, narrow-band picosecond radiation in the mid-infrared by difference frequency mixing in GaSe and CdSe

We report on the generation of tunable, narrow-band picosecond laser pulses in the mid-IR at 1 kHz repetition rate. An optical parametric oscillator (OPO) seeded optical parametric amplifier (OPA) delivers signal and idler pulses with energies of several hundred microjoule tunable between 1.56 and 3.24 μm. Difference frequency mixing of the OPA signal and idler waves permits the generation of mid-IR radiation between 3 and 24 μm. The laser system therefore permits full coverage of the wavelength range between 1.6 and 24 μm. Conversion efficiencies greater than 50% and pulse energies up to 40 μJ are obtained with GaSe.

Phase-matching and femtosecond difference-frequency generation in the quaternary semiconductor AgGaGe5Se12.

We present data on the linear (transmission, index of refraction) and nonlinear (second-order susceptibility) optical properties of the quaternary semiconductor AgGaGe5Se12 with orthorhombic symmetry--a solid solution in the AgxGaxGe1-xSe2 system with x = 0.17. The nonlinear coefficients are estimated from phase-matched second-harmonic generation near 3 microm. After numerical analysis of the phase-matching configurations for three-wave nonlinear interactions, the first experimental results on difference-frequency mixing, producing tunable (4-7.5-microm) femtosecond pulses at a 1-kHz repetition rate, are described. The pulses of only five optical cycles (FWHM = 84 fs) are generated near 5 microm with energy of 0.5 microJ. Because of its higher damage threshold, larger birefringence and bandgap, and greater variety of phase-matching schemes, AgGaGe5Se12 could become an alternative to AgGaS2 and AgGaSe2, more widely used in high-power and specific applications.

Fresnel phase matching for three-wave mixing in isotropic semiconductors

We deal with phase matching of three-wave mixing by total internal reflection in isotropic semiconductors. This technique makes use of the large relative phase lag between the three interacting waves at total internal reflection, as described by Augustin Fresnel. This is why we denote this technique as Fresnel phase matching. The theory of Fresnel phase matching is developed with a propagation matrix method: It allows us to describe the conditions (sample thickness, polarization, tuning angles, etc.) for phase matching, the influence of surface roughness, and the walk-off effects due to Goos–Hänchen shifts. Moreover, we show that nonresonant phase matching strongly alleviates the phase-matching tolerance while keeping good conversion yields. The potential of this technique is demonstrated by largely tunable mid-infrared generation (between 7 and 13 μm with a single sample) by use of difference-frequency mixing of two near-infrared sources. Excellent agreement between the presented theory and experiments is demonstrated both in GaAs and ZnSe samples.

High energy and narrow bandwidth mid IR nanosecond laser system

In this paper a high energy, tunable nanosecond laser system in the region of 6 μm is introduced. The laser contains three units. Via a difference frequency mixing IR-light at about 2.6 μm is generated, in a subsequent optical parametric amplifier process signal and idler at about 2.6 and 1.8 μm are produced, respectively. In the third unit the IR-light about 6 μm is produced by a difference frequency mixing of signal and idler in an AgGaSe2 crystal. The spectral bandwidth of the IR laser is better than 0.1 cm−1 and a laser energy of at least 1 mJ (at 10 ns pulse length) can be achieved. The laser is ideally suited to record IR spectra in the region of CO stretching and NH bending vibrations.

One-photon mass-analyzed threshold ionization spectroscopy of 1,3,5-trifluorobenzene: the Jahn-Teller effect and vibrational analysis for the molecular cation in the ground electronic state.

One-photon mass-analyzed threshold ionization spectrum of 1,3,5-trifluorobenzene was obtained by using vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. The Jahn-Teller parameters for the e' modes (nu(8)-nu(14)) of 1,3,5-C(6)H(3)F(3)(+) in the ground electronic state needed for spectral analysis were taken from the density functional theory results initially and were upgraded through fits to the experimental results. Excellent agreement was achieved between the experimental and calculated Jahn-Teller energy levels. Assignments of the Jahn-Teller inactive modes were accomplished by referring to the calculated frequencies and the selection rule. The ionization energy of 1,3,5-trifluorobenzene determined from the position of the 0-0 band was 9.6359+/-0.0006 eV.

Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of hexafluorobenzene: the Jahn-Teller effect and vibrational analysis.

One-photon mass-analyzed threshold ionization (MATI) spectrum of hexafluorobenzene was obtained by using vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. The ionization energy of hexafluorobenzene determined from the position of the 0-0 band was 9.9108+/-0.0006 eV. To aid the spectral analysis, the Jahn-Teller coupling parameters for four e(2g) modes of C(6)F(6) (+) in the ground electronic state were calculated from the topographical data of the potential energy surface obtained at the density functional theory (DFT) level. These were used in the initial calculation of the energies of the Jahn-Teller states and upgraded through the multimode fit to the experimental data. Excellent agreement between the experimental and calculated frequencies was achieved. The vibrations which are not linear Jahn-Teller active were observed and could be assigned by referring to the frequencies obtained at the DFT level.

Collinear phase-matched terahertz-wave generation in GaP crystal using a dual-wavelength optical parametric oscillator

Tunable terahertz (THz)-wave generation in GaP crystal was theoretically and experimentally investigated using collinear difference frequency mixing. The wavelength range and length of GaP crystal for efficient difference frequency generation (DFG) were determined by calculating the phase-matching conditions. THz waves from 0.5 to 4.5 THz were generated by collinear phase-matched DFG using a dual-wavelength optical parametric oscillator with two KTiOPO4 crystals in the range of 930–1000 nm. A maximum THz output energy of 5.3 nJ/pulse (peak power of 0.66 W) at 1.9 THz was obtained when the pump energy was 1.2 mJ/pulse.

Midinfrared difference frequency generation in quasi-phase matched diffusion bonded ZnSe plates

We present the results on tunable midinfrared radiation (8–12 μm) generated in diffusion-bonded ZnSe slabs by difference frequency mixing of optical-parametric-oscillator output waves (≈2 μm).

Widely tunable terahertz-wave generation in an organic crystal and its spectroscopic application

Terahertz (THz)-wave generation using difference-frequency mixing in an organic 4-N, N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) crystal was investigated theoretically and experimentally. We developed a dual-wavelength optical parametric oscillator (OPO) with two KTiOPO4 crystals as the input light source. This oscillator has a tunable range from 1300–1450 nm and is pumped by a diode-pumped, frequency-doubled, Q-switched Nd:YAG laser with a pulse duration of 10 ns. Widely tunable THz waves ranging from 2 to 20 THz were generated from DAST crystals with 0.5- and 1-mm thickness using the OPO. THz output energies of 82 nJ (peak power of 10.3 W) at 11.6 THz and 110 nJ (peak power of 13.8 W) at 19 THz were obtained with a 1-mm-thick DAST crystal. Using a tunable THz-wave system consisting of the THz source and a pyroelectric detector, THz spectroscopic data for a polytetrafluoroethylene sheet were obtained and were comparable to data obtained from a conventional far-infrared spectrometer.

New design for a time-of-flight mass spectrometer with a liquid beam laser desorption ion source for the analysis of biomolecules

We describe a novel liquid beam mass spectrometer, based on a recently discovered nanosecond laser desorption phenomenon, [W. Kleinekofort, J. Avdiev, and B. Brutschy, Int. J. Mass Ion. Processes 152, 135 (1996)] which allows the liquid-to-vacuum transfer, and subsequent mass analysis of pre-existing ions and ionic associates from liquid microjets of aqueous solutions. The goal of our novel technical approach is to establish a system with good mass resolution that implements improvements on critical components that make the system more reliable and easier to operate. For laser desorption pulsed dye-laser difference frequency mixing is used that provides tunable infrared light near the absorption maximum of liquid water around 3 μm. Different types of liquid beam glass nozzles (convergent capillary and aperture plate nozzles) are investigated and characterized. Starting from theoretical considerations of hydrodynamic drag forces on micrometer size droplets in supersonic rarefied gas flows we succeeded in capturing efficiently the liquid beam in a liquid beam recycling trap operating at the vapor pressure of liquid water. For improving the pollution resistance, the liquid jet high vacuum ion source region is spatially separated from the reflectron time-of-flight mass spectrometer (TOF–MS) working behind a gate valve in an ultrahigh vacuum environment. A simple (simulation optimized) ion optics is employed for the ion transfer from the source to the high vacuum region. This new feature is also mostly responsible for the improved mass resolution. With the present tandem-TOF–MS setup a resolution of m/Δm≈1800 for the low and m/Δm≈700 in the high mass region has been obtained for several biomolecules of different mass and complexity (amino acids, insulin, and cytochrome c).

Highly efficient narrow-line generation by difference-frequency mixing of a green pump and the stokes seed in RbTiOPO4 crystals: excitation of 943-nm emission.

An efficient and compact scheme for diode-pumped Nd:YLF laser wavelength conversion to 943 nm was demonstrated by use of difference-frequency mixing and stimulated Raman scattering. We believe that this is the highest conversion efficiency from the laser fundamental wavelength reported to date. It is shown that RbTiOPO4 crystals are capable of providing highly efficient frequency mixing as a nonlinear medium.

Zero-additional-phase SPIDER: full characterization of visible and sub-20-fs ultraviolet pulses

We demonstrate a novel spectral-shearing interferometry setup for characterizing the temporal amplitude and phase of ultrashort optical pulses over an extremely wide wavelength region. By the mixing of two strongly chirped auxiliary pulses with the pulse to be characterized, two spectrally sheared replicas are generated, and their spectral interference is evaluated. We fully characterize 10-fs pulses in the visible region by sum-frequency mixing and 19-fs pulses in the ultraviolet region by difference-frequency mixing. The scheme is self-referencing and highly sensitive. The zero-additional-phase scheme does not alter the unknown pulses and yields the pulse shape at the interaction point of a spectroscopic experiment.

Continuously tunable THz and far-infrared wave generation from DAST crystal

Continuously tunable terahertz (THz) and far-infrared waves over a wide range of 2 to 30 THz were generated in a 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) crystal by difference frequency mixing. A dual-wavelength optical parametric oscillator in the range of 1250 to 1450 nm as the input light source was developed.

Continuously tunable terahertz-wave generation in GaP crystal by collinear difference frequency mixing

Tunable terahertz (THz)-wave generation from 0.5 to 4.5 THz has been achieved in a GaP crystal by collinear difference frequency mixing of dual wavelengths in the range 940–1000 nm. THz output energy of 5 nJ/pulse at 2.6 THz was obtained when the pump energy was 1.2 mJ/pulse.

Widely-tunable THz-wave generation in 2–20 THz range from DAST crystal by nonlinear difference frequency mixing

Widely-tunable terahertz (THz)-wave generation from 2 to 20 THz can be achieved in DAST crystal by collinear mixing of dual wavelengths in the range 1300–1450 nm. Output energy of 12 nJ/pulse at 4.4 THz and 152 nJ/pulse at 19 THz was obtained at pump energy of 0.6 mJ/pulse.

One-photon mass-analyzed threshold ionization spectroscopy of 2-bromopropene (2-C3H5Br): Analysis of vibration and internal rotation in the cation

Vibrational spectrum of 2-C3H5Br cation in the ground electronic state was obtained by one-photon mass-analyzed threshold ionization (MATI) spectroscopy using coherent vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. From the MATI spectra, ionization energy of 2-C3H5Br to the ionic ground state has been determined to be 9.4377±0.0006 eV. Vibrational assignments have been made by comparing with the vibrational frequencies and Franck-Condon factors calculated at the B3LYP and BP86 levels with the 6-311++G(3df,3pd) basis set. Several low-frequency bands have been assigned to the torsional motion of the methyl group in the cation. Energies of the torsional states and relative transition intensities to these states have been reproduced well by a one-dimensional rotor model. The torsional barrier and internal rotational constant have been determined to be 80.0 and 5.13 cm−1, respectively.

One-Photon Mass-Analyzed Threshold Ionization Spectroscopy of trans- and cis-1-C3H5Br: Ionization Energies and Vibrational Assignments for the Cations

Vibrational spectra of trans- and cis-1-C3H5Br cations in the ground electronic states were obtained by the one-photon mass-analyzed threshold ionization (MATI) spectroscopy using the coherent vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. From the MATI spectra, ionization energies of trans- and cis-1-C3H5Br to the ionic ground states have been determined to be 9.2693 ± 0.0006 and 9.3140 ± 0.0006 eV, respectively. Almost complete vibrational assignments for the peaks in the MATI spectra were possible by utilizing vibrational frequencies and Franck−Condon factors calculated at the B3LYP and BP86 levels with the 6-311++G(3df,3pd) basis set.

Vibrational Analysis of Vacuum Ultraviolet Mass-Analyzed Threshold Ionization Spectra of Phenylacetylene and Benzonitrile

One-photon MATI spectra of phenylacetylene and benzonitrile were obtained by using vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. Accurate ionization energies of phenylacetylene and benzonitrile were determined from the positions of the 0−0 bands, which are 8.8195 ± 0.0006 and 9.7288 ± 0.0006 eV, respectively. Vibrational frequencies of the molecular ions were determined from the spectra also. Assignments were made by utilizing the symmetry selection rule and frequencies and Franck−Condon factors calculated at the BP86, B3LYP, and B3PW91 density functional theory levels with the 6-311++G(2df,2pd) basis set.

Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of vinyl bromide: Franck–Condon analysis and vibrational assignment

Vibrational spectrum of vinyl bromide cation in the ground electronic state was obtained by one-photon mass-analyzed threshold ionization (MATI) spectroscopy using coherent vacuum ultraviolet radiation generated by four-wave difference frequency mixing in Kr. From MATI spectrum, ionization energy to the ground state of the cation was determined to be 9.8171±0.0006 eV (79 180±5 cm−1). Almost complete vibrational assignments for the peaks in the MATI spectrum were possible by utilizing vibrational frequencies and Franck–Condon factors calculated at the Becke three parameter Lee–Yang–Parr (B3LYP)/6-311++G(df,pd) level. Franck–Condon analysis for one-photon MATI spectra is especially useful because calculations of only the ground electronic states are involved while that for two-photon MATI spectra requires excited state calculations.