Difference Frequency Mixing Research Articles

Temperature tuning of 5–12 μm by difference frequency mixing of OPO outputs in a AgGaS2 crystal

We report a temperature tuned mid-IR generating system ranging from 5 to 12 μm by difference frequency mixing of output waves from two optical parametric oscillators (OPOs) in a silver gallium sulfide (AgGaS2) crystal. One of the OPOs generate signal wave of 1.6 μm, while the other produced tunable radiation from 1.846 to 2.353 μm. The AgGaS2 crystal is temperature tuned to allow phasematching for tunable output from 5 to 12 μm.

Femtosecond pulse shaping in the mid infrared by difference-frequency mixing

The generation of programmable complex femtosecond pulses in the mid infrared (3–10 μm) with high precision is reported. Designed pulse shapes in the near infrared (1–1.6 μm) are transferred to the mid infrared via difference-frequency mixing with a second infrared pulse spectrally narrowed in a zero-dispersion compressor. In particular, pulse sequences with variable relative phases have been obtained. The control of the pulse properties is achieved purely electronically, allowing for implementation into a feedback loop.

Direct field-resolved detection of terahertz transients with amplitudes of megavolts per centimeter.

Phase-matched difference-frequency mixing in a thin GaSe crystal within the broad spectrum of 25-fs pulses from a Ti:sapphire oscillator multipass amplifier system permits the generation of few-cycle electric field transients, frequencies up to 30 THz, and amplitudes of more than 1 MV/cm. The field transients generated at a 1-kHz repetition rate are directly measured by electro-optic sampling by 12-f probe pulses from the 75-MHz repetition-rate Ti:sapphire oscillator in combination with a novel electronic gating technique.

Performance Characteristics of Narrow Linewidth Fiber Laser Pumped Mid-IR Difference Frequency Mixing Light Source for Methane Detection

A high-power, narrow-linewidth Yb fiber laser with a fiber Bragg grating (FBG) pumped difference frequency generation (DFG) in a periodically poled lithium niobate (PPLN) crystal was investigated in detail. A mid-IR power of ∼2.3 µW at 3.3 µm with a slope efficiency of 0.85 mW/W2 was achieved. A Doppler-broadened absorption spectrum of CH4 at 3038.497 cm-1 (3.2911 µm) was obtained with a 0.1-m long-gas cell at a pressure of 133 Pa. The linewidth of the DFG source was evaluated to be less than 96 MHz from the observed spectral linewidth. Real-time monitoring of CH4 (∼1.78 ppm) in ambient air in a multipass cell which has an optical path length of 10 m was also demonstrated.

All-optical time-division demultiplexing of 160 Gbit∕s signal using cascaded second-order nonlinear effect in quasi-phase matched LiNbO3 waveguide device

Using the cascade of the second-harmonic generation and the difference frequency mixing in a 30 mm-long quasi-phase matched LiNbO3 waveguide device, all-optical time-division demultiplexing of a 160 Gbit/s signal into 10 Gbit/s channels is demonstrated. The power penalty is as small as 2.5 dB at the bit error rate of 10−9, which is attributed to crosstalk of the switch.

Electro-optic detection of continuous-wave mid-infrared radiation

We demonstrate coherent detection of continuous-wave mid-infrared radiation. This radiation is produced by use of conventional difference-frequency mixing and detected via the linear electro-optic effect. The detection process allows for the simultaneous measurement of the amplitude and phase properties of the infrared field. Both processes require an amplitude-modulated optical beam that is derived from the superimposed output of two single-frequency lasers. With appropriate choice of lasers and nonlinear optical crystals, the technique may be applied to any wavelength throughout the far and mid infrared.

Novel design method for all-optical ultrafast gate switches using cascaded second-order nonlinear effect in quasi-phase matched LiNbO3 devices

The authors propose a novel method of designing all-optical ultrafast gate switches that employ the cascade of the second harmonic generation and difference frequency mixing in quasi-phase matched LiNbO/sub 3/ devices. In this design method, the device length is maximized under the condition that crosstalk of the switch is maintained below a certain allowable value at a given bit rate. Following the design method, the authors find that the switching efficiency can significantly be enhanced by compensation for the walkoff between the fundamental and second harmonic pulses.

Design of polarization retarder suitable for nonlinear optical systems

We present a design technique of retarders suitable for nonlinear optical systems. A thin sample of LiNbO 3 crystal is utilized as a retarder for wide-ranging applications. Analysis shows that the same crystal can be used for single-wave or two-wave retardations, changing the orientation of the crystal only. As an application, the retarder is used to polarize two waves orthogonal, as necessary for difference frequency mixing in an AgGaSe 2 crystal.

Optimal design and applications for quasi-phase-matching three-wave mixing

Solutions of quasi-phase-matching three-wave mixing (TWM) for a nonuniform grating structure with phase-shifted segments are derived by use of a matrix operator, for the first time to the authors' knowledge, under the small-signal approximation. Compared with iterative methods of coupled-mode equations, using these expressions can significantly shorten the calculation time, and they can be effectively applied to all-optical signal processing in TWM. The signal and pump bandwidths of wavelength conversion in difference-frequency mixing, as well as the all-optical gating bandwidth in sum-frequency mixing, are optimized with the matrix solutions. By comparison with loss-free waveguide, the propagation loss a of the waveguide decreases the conversion efficiency /spl eta/, but has little influence on the bandwidth. Numerical results show that /spl alpha/ can be ignored for nonlinear lengths L<20 mm, and the optimal bandwidth /spl Delta//spl lambda/ is sensitive to /spl eta/ and the variation in the grating period, but not to /spl alpha/.

Difference-frequency mixing of output waves from a periodically poled lithium niobate optical parametric oscillator in a GaSe crystal

We report on an optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN) pumped by a Nd:YAG laser, and on extending its tuning range by difference-frequency mixing of OPO output waves in GaSe crystal. Maximum combined signal and idler pulse energy of 2.7 mJ and slope efficiency of 25% have been achieved. The tuning range is 1.71 to 1.98 mm for the signal wave and 2.81 to 2.30 mm for the idler wave, using a single set of mirrors. As an application of this PPLN OPO, the signal and the idler waves are difference-frequency- mixed in a GaSe crystal to produce tunable mid-IR from 4.35 to 14.25 mm. The efficiency of the mixing has been analyzed, considering the experimental results. © 2002 Society of Photo-Optical Instrumentation Engineers.

Efficient generation of &lt;3-cm^-1 bandwidth mid-IR pulses by difference-frequency mixing of chirped pulses

We report on a laser system that produces near-transform-limited picosecond pulses in the 3–5-µm wavelength range with bandwidths adjustable from values close to the pump bandwidth (∼16 cm-1) to more than fivefold narrower bandwidths (<3 cm-1) and with the pulse energies that exceed 48 µJ at 3 µm and 5 µJ at 5 µm. The system employs difference-frequency mixing in a potassium titanyl arsenate crystal pumped by an amplified Ti:sapphire laser and seeded by a traveling-wave optical parametric generator. The difference-frequency bandwidth narrowing is achieved by equal chirping of the seed and the pump pulses with two pulse stretchers before mixing.

High-energy sub-picosecond pulse generation from 3 to 20 μm

We have produced sub-picosecond pulses in the wavelength range 3–20 μm with energies as high as 2 μJ, through difference-frequency mixing in the crystal GaSe. Input beams for the non-linear mixing process came from either a regenerative amplifier operating in two-color mode, due to the spectral shaping of its injection beam, or an optical parametric amplifier (OPA). The first method was straightforward to implement and provided easy access to the wavelength range 10–20 μm. The intermediate OPA stage, though technically more involved, allowed higher input beam irradiances and resulted in shorter duration MIR pulses, greater conversion efficiency and access to the MIR region between 3 and 10 μm.

Self-sum- and -difference-frequency mixing in GdAl_3(BO_3)_4:Nd^3+ for generation of tunable ultraviolet and infrared radiation

We exploited Nd(3+) laser emission at 1061.9 nm ((4)F(3/2)?(4)I(11/2) channel) in a self-chi((2)) active GdAl(3)(BO(3))(4):Nd(3+) laser crystal. UV radiation was obtained from a 1.8% yield from self-sum-frequency mixing: 1/pump + 1/1061.9 = 1/UV, during pumping in the Nd(3+) (4)G(5/2)-(2)G(7/2) levels near 588 nm. The UV tunability had a range of 378-382 nm. We have demonstrated, for the first time to our knowledge, generation of coherent IR radiation from a self-difference-frequency mixing laser: 1/pump - 1/1061.9 = 1/IR. We got a 0.5% yield and tunability in the 1305-1365-nm range.

Largely tunable midinfrared (8–12 μm) difference frequency generation in isotropic semiconductors

Largely tunable midinfrared (8–12 μm) generation is obtained in GaAs and ZnSe slabs by difference frequency mixing of optical parametric oscillator output waves (∼2 μm). The coherence lengths determined in semiconductor wedges are in excellent agreement with estimates from known Sellmeir formulas.

Evaluation of Nd 3+-doped BiB 3O 6 (BIBO) as a new potential self-frequency conversion laser crystal

We present at room temperature emission and absorption spectra of new-synthesised Nd 3+-doped BiB 3O 6 (BIBO) in X-, Y-, Z-polarisations. The measured Nd 3+ concentration in the crystal remains low (1.08×10 19 ions/cm 3) and prevents up to now laser oscillation. The Judd–Ofelt analysis was performed with the results: Ω 2X=0 cm 2 , Ω 4X=0.556×10 −20 cm 2 , Ω 6X=0.227×10 −20 cm 2 , Ω 2Y=0 cm 2 , Ω 4Y=0.307×10 −20 cm 2 , Ω 6Y=0.177×10 −20 cm 2 , Ω 2Z=0.069×10 −20 cm 2 , Ω 4Z=0.433×10 −20 cm 2 , Ω 6Z=0.117×10 −20 cm 2 . The highest emission cross-section near 1079 nm is 2.2×10 −20 cm 2 . The 4 F 3/2 emission lifetime is 53 μs . Low temperature spectroscopy reveals that there is only one kind on Nd 3+ emitting centre which substitutes Bi 3+ cations. We evaluate the ability of the material to be a self-frequency conversion laser crystal by calculating the phase matching directions, the effective nonlinear optical coefficients and the effective emission cross-sections for self-frequency doubling, self-sum and difference frequency mixing. We have found that the emission peak at 1069 nm existing mainly for Y-polarisation was the most favourable with directions of propagations in the YZ-plane ( φ=90°) for self-sum frequency mixing and in the XZ-plane ( φ=0°) for the self-difference frequency mixing. For these directions the effective nonlinear optical coefficient (up to 3.2 pm/V) and the effective emission cross-section have simultaneously the highest values.

COMPARATIVE VERY-HIGH-RESOLUTION VUV SPECTROSCOPY: LASER SPECTROSCOPY OF O2

Despite their importance to the photochemistry of the terrestrial atmosphere, and many experimental studies, previous characterization of the Schumann–Runge (SR) bands of O 2, [Formula: see text] (1750–2050 Å) has been limited by poor experimental resolution. In addition, our understanding of the SR spectrum is incomplete, many rovibrational transitions in the perturbed region of the spectrum [B(v &gt; 15)] remaining unassigned. We review new very-high-resolution measurements of the O 2 photoabsorption cross section in the SR bands. Tunable, narrow-bandwidth background vacuum-ultraviolet (VUV) radiation for the measurements (~ 7 × 105 resolving power) was generated by the two-photon-resonant difference-frequency four-wave mixing in Xe of excimer-pumped dye-laser radiation. With the aid of these cross-section measurements, rovibrational and line-shape analyses have led to new insights into the molecular structure and predissociation dynamics of O 2. The current VUV laser-spectroscopic measurements are shown to compare favourably with results from two other very-high-resolution experimental techniques, namely laser-induced fluorescence spectroscopy and VUV Fourier-transform spectroscopy, the latter performed using a synchrotron source.

Experimental and theoretical investigation of generation of a cross-polarized wave by cascading of two different second-order processes

A nonlinear optical effect in which a linearly polarized wave propagating in a single quadratic medium is converted into a wave that is cross polarized to the input wave is investigated theoretically and observed experimentally in β-barium borate crystal. It is proved that this effect is a result of cascading of two different second-order processes. It starts with the generation of an extraordinary second-harmonic wave by type I interaction and is followed by type II difference-frequency mixing between the second-harmonic wave and the ordinary fundamental wave. The experiment was performed (a) for phase-matched type I interaction and non-phase-matched type II interaction and (b) for non-phase-matched type I interaction and phase-matched type II interaction. The observed generation of a cross-polarized wave is to our knowledge the only cubic effect whose first manifestation has been observed in quadratic crystal.

Mid-infrared pulses generated from the mixing output of an amplified, dual-wavelength Ti:sapphire system

We demonstrate the generation of femtosecond mid-infrared pulses by direct difference-frequency mixing in a AgGaS(2) crystal of two intense pulses from a dual-wavelength oscillator that have been simultaneously amplified in a single regenerative amplifier. A pulse energy of as much as 1.6 muJ was achieved at wavelengths of 9-11 mum.

Programmable amplitude- and phase-modulated femtosecond laser pulses in the mid-infrared

We present a scheme to produce programmable phase- and amplitude-modulated femtosecond laser pulses in the mid-infrared regime of 3-10mum by difference frequency mixing. The 80-fs signal output of an optical parametric amplifier is shaped with a liquid-crystal mask and mixed in an AgGaS(2) crystal with a temporally stretched idler pulse. Without changing the mechanical alignment, we produce programmable amplitude modulations and chirped pulses at lambda=3mum with energy as high has thas 1muJ . This scheme, further, allows the generation of controllable pulse sequences. The results are in good agreement with theoretical simulations.

Electro-optic polymer based devices and technology for optical telecommunication

Electro-optic polymer waveguide devices are very attractive for optical communication systems, because of their potentially simple and low-cost fabrication procedure. High bandwidth devices are enabled by the low dielectric constant of polymers with negligible dispersion from DC to optical frequencies. We first detail the modelization steps relating to the optical and electrical aspects of devices. We then outline the different steps of the fabrication process of electro-optic polymer based devices. By way of illustrating these considerations, we present some original realizations namely polarization insensitive modulators, switching devices using an asymetric X coupler and optic to RF converters based on difference frequency mixing. To cite this article: P. Labbé et al., C. R. Physique 3 (2002) 543–554.