Periodically Poled Lithium Niobate Crystal Research Articles

Tunable dual-signal PPLN optical parametric generator by using an acousto-optic beam splitter

A tunable dual-signal optical parametric generator (OPG) based on multi-grating periodically poled lithium niobate (PPLN) is presented. An acousto-optic device (AOD) was used as a beam splitter outside the cavity of a high-repetition-rate, Q-switched 1064 nm Nd:YAG laser. A synchronous and widely tunable dual-signal OPG was obtained by coupling the split beams into two parts with different poled periods in the same PPLN crystal and by tuning the temperature of the crystal. A total conversion efficiency of 27.9% was achieved when the system operated at 1687 and 1864 nm.

Electro-optic periodically poled lithium niobate Bragg modulator as a laser Q-switch

We report an electro-optic Bragg modulator using a periodically poled lithium niobate (PPLN) crystal. We measured a half-wave voltage of 160 V when transmitting a 1064 nm laser through a 14.2 mm long, 780 microm thick, 20.13 microm period PPLN crystal at the Bragg angle. We also demonstrated a Q-switched Nd:YVO(4) laser using such a PPLN Bragg modulator as its Q-switch, producing 7.8 ns, 201 microJ pulses at a 10 kHz repetition rate when pumped by a 19.35 W diode laser at 808 nm.

Monolithically integrated laser Bragg Q-switch and wavelength converter in a PPLN crystal

We report a periodically poled lithium niobate (PPLN) crystal for both temperature-insensitive laser Q-switching and temperature-tuned wavelength conversion. The PPLN crystal consists of two sections, a 20.3-mum period section functioning as an electro-optic Bragg grating for Qswitching a diode-pumped Nd:YVO4 laser at 1064 nm and a 31-mum-period section functioning as an optical parametric generator for down converting the generated 1064-nm laser. When driving the PPLN Bragg grating with 170-V voltage pulses, we measured 181 muJ pulse energy at 1064 nm from the Nd:YVO4 laser pumped by 20.4 W diode power. The 181-muJ pulsed laser was further converted into mid-infrared radiation in the monolithic PPLN crystal with 35% parametric efficiency. The wavelengths were broadly tunable in the range of 1.75-1.88 mum (signal) and 2.7-2.44 mum (idler) via temperature without affecting the performance of the PPLN Bragg Qswitch.

Ultra-broadband optical parametric generation and simultaneous RGB generation in periodically poled lithium niobate

We report on efficient collinear optical parametric generation (OPG) with gain band ranging from 1400 to 2600 nm in a 2 cm-long periodically poled lithium niobate (PPLN) crystal. Such an ultra-broad gain band was obtained by choosing the pump wavelength at 933 nm, at which the group-velocities of the signal and the idler match near the degeneracy point. High OPG efficiency was obtained by quasi-phase matching (QPM). The ultra-broadband OPG led to efficient collinear RGB generation from a single PPLN crystal at a fixed pump wavelength. The green and red beams were found to be originating from high-order QPM sum-frequency generation between the pump and selected frequencies in the OPG band, while the blue beam was high-order QPM second-harmonic generation of the pump.

Energy exchange between two orthogonally polarized waves by cascading of two quasi-phase-matched quadratic processes

We demonstrate energy exchange between two orthogonally polarized optical waves as a consequence of a two-color multistep parametric interaction. The energy exchange results from cascading of two quasi-phase-matched (QPM) second-harmonic parametric processes, and it is intrinsically instantaneous. The effect is observed when both the type-I (ooe) second-harmonic generation process and higher QPM order type-0 (eee) second-harmonic generation processes are phase-matched simultaneously in a congruent periodically-poled lithium niobate crystal. The two second-harmonic generation processes share a common second-harmonic wave which couple the two cross-polarized fundamental components and facilitate an energy flow between them. We demonstrate a good agreement between the experimental data and the results of numerical simulations.

BANDWIDTH ENHANCEMENT METHODS OF TELECOM-REGION ENTANGLED TWIN PHOTONS VIA QUASI-PHASE-MATCHED SPONTANEOUS PARAMETRIC DOWN-CONVERSION

We theoretically present the bandwidth enhancement methods of the telecom-region entangled twin photons generated by quasi-phase-matched (QPM) spontaneous parametric down-conversion (SPDC) in periodically poled lithium niobate (PPLN) crystals. By using type I (e → e + e) SPDC, the degenerate entangled twin photons will have a broad bandwidth and it can be further enhanced by shortening the crystal length, detuning the pump wavelength or adjusting the working temperature of the PPLN crystal. This principle provides the possibility to introduce wavelength-division-multiplexed technique into quantum information systems.

Efficient single-photon counting at 1.55μm by intracavity frequency upconversion in a unidirectional ring laser

A single-photon signal at 1.55μm was converted to its visible replica by sum-frequency mixing with a strong intracavity pump of a unidirectional ring laser at 1.06μm in a periodically poled lithium niobate (PPLN) crystal. In the ring laser configuration, standing-wave photorefractive effects in the PPLN crystal could be suppressed and consequently, the spectral bandwidth of the intracavity pump could be controlled for excellent quasi-phase-matching. A conversion efficiency of 96% was demonstrated, and the corresponding background counts were less than 6.0×105s−1. The single-photon upconversion was used for efficient single-photon counting at 1.55μm with long-term stability.

Non-collinear and non-degenerate polarization-entangled photon generation via concurrent type-I parametric downconversion in PPLN

A periodically poled lithium niobate (PPLN) crystal has been used as an efficient source of non-collinearly generated polarization-entangled photon pairs at 810 and 1550 nm. The PPLN crystal was endowed with a specially designed poling pattern and the entangled photons were generated via the nonlinear optical process of spontaneous parametric down conversion (SPDC). A novel design based on overlapping two concurrent type-I quasi-phase-matching structures in a single PPLN crystals produced correlated pairs of alternatively polarized photons in largely separated spectral regions. The phase of the resulting two-photon state is directly linked to parameters of the nonlinear grating. Continuous tunability of the generated Bell state, from Phi(+) to Phi(-), has been demonstrated by translating a slightly wedged crystal perpendicular to the pump beam.

THz Generation and Detection in Periodically Poled Lithium Niobate Crystal

We report the parametric interaction between terahertz (THz) wave and ultrafast optical wave in periodically poled lithium niobate (PPLN) crystal. A THz wave with frequency of 1.37 THz was generated as femtosecond pump pulse propagated through the PPLN crystal with grating periods of 30 μ m. The pump-induced THz wave interacts with the probe wave in the crystal by frequency mixing. The THz-wave-modulated probe beam is easily detected by a normal photodiode. A new method for detecting time-domain THz wave with commercial photodiode was proposed.

Online monitoring of ethane traces in exhaled breath with a difference frequency generation spectrometer

We report a transportable mid-infrared laser cavity leak-out spectrometer for online detection of trace gases. The laser spectrometer is based on continuous-wave difference-frequency generation in the wavelength region around 3 μm. Sensitive spectroscopic trace gas monitoring was achieved using a high-finesse ring-down cavity. For difference-frequency generation, we use a periodically poled lithium niobate (PPLN) crystal, pumped by a Nd:YAG laser (signal wave) and a diode laser (pump wave) with a tapered amplifier. A maximum power of 280 μW near λ=3.3 μm is achieved using a pump power of 180 mW at 807 nm, a signal power of 890 mW at 1064.46 nm, and a 50-mm-long PPLN crystal. The resulting system proved to be a unique tool with high sensitivity and specificity for rapid and precise breath testing. We demonstrate spectroscopic online monitoring of ethane traces in exhaled human breath with a precision of 270 parts per trillion (1σ) and a time resolution of 1 s.

Surface-emitted terahertz-wave difference-frequency generation in two-dimensional periodically poled lithium niobate

We report on the demonstration of surface-emitted terahertz- (THz-) wave difference-frequency generation from two-dimensional (2D) periodically poled lithium niobate (PPLN). The two orthogonal periodic structures individually compensate for both the phase mismatch of the launched lasers and the generated THz wave. Tunable 1.5-1.8 THz wave generation with a bandwidth of 10-GHz was obtained by use of two 2D PPLN crystals. We also confirmed that THz waves were simultaneously generated into two opposite directions, which suggests the possibility of higher THz-wave output power.

High power output quasi-continuous-wave nanosecond optical parametric generator based on periodically poled lithium niobate

We report on a high power output quasi-continuous-wave nanosecond optical parametric generator (OPG) of congruent periodically poled lithium niobate (PPLN) pumped by a 1064 nm acousto-opticallyQ-switched Nd: YVO4 laser (duration: 70 ns, repetition rate: 45 kHz, spatial beam qualityM2< 1.3). The OPG consists of a 38.7 mm long PPLN crystal with a domain period of 28.93 μ. With 5.43 W of average pump power the maximum average output power is 991 mW at 1517.1 nm signal wave of the PPLN OPG.

High-Average-Power Nanosecond Quasi-Phase-Matched Single-Pass Optical Parametric Generator in Periodically Poled Lithium Niobate

A pulsed nanosecond optical parametric generator (OPG) in periodicallypoled lithium niobate (PPLN) crystal is presented. The pump laser is anacousto-optically Q-switched Nd:YVO4 laser with themaximum average power of 6.58 W. When the repetition rate is 50 kHz andthe pulse width of the pump source is 80 ns, the maximum average totaloutput power of the single-pass PPLN OPG is about 1.9 W, which includes1.322 W of 1.536 μm signal radiation. The length of the PPLNcrystal is only 38.7 mm (at room temperature) with a grating period of28.93 μm (at room temperature). The 1.502–1.536 μm signalradiation and 3.652–3.465 μm idler radiation are obtained byadjusting the PPLN crystal temperature from 155 degrees C to 250 degrees C.

Atmospheric detection of N2O and CO2 with a pulsed optical parametric oscillator

Nitrous oxide (N 2 O) concentrations in ambient air were measured by photoacoustic spectroscopy. The light source, a grazing-incidence optical parametric oscillator (GIOPO) with a periodically-poled lithium niobate (PPLN) crystal, was pumped by a pulsed Nd:YAG laser. Measurements were performed in the spectral region of 2.76-2.91 μm containing N 2 O, CO 2 , and water absorption lines. Two serial water filters filled with CaCl 2 and P 2 O 5 were used to reduce the concentration of water to the level of several pans per billion by volume (ppbv). Using a standard mixture of 50.6 parts per million by volume (ppmv) of N 2 O in synthetic air to calibrate the photoacoustic signal, a value of 310 ′ 30 ppbv was found for the concentration of N 2 O in the ambient atmosphere.

Monolithic quasi-phase-matched nonlinear crystal for simultaneous laser Q switching and parametric oscillation in a Nd:YVO_4 laser

We report the performance of a periodically poled lithium niobate (PPLN) crystal inside a diode-pumped Nd:YVO4 laser for simultaneous laser Q switching and optical parametric oscillation. The monolithic PPLN crystal consists of two sections, a 1-cm-long 14-microm-period electrode-coated section and a 4-cm-long 30-microm-period section, functioning as a low-voltage Pockels cell and a quasi-phase-matched parametric gain medium, respectively. At a 150-V Q-switching voltage and a 6-kHz switching rate, we measured 25-microJ pulse energy and 4-kW peak power at 1.55 microm with 9-W absorbed diode power.

Doppler-free spectroscopy of xenon in the mid-infrared using difference-frequency radiation

We report on the first Doppler-free spectroscopy investigation of an atomic species, xenon, performed in the mid-infrared using difference-frequency radiation. The absorption saturated spectrum of the xenon 6p[3/2]2?5d[5/2]3 transition (2p6?3d'1 in Paschen notation) at 3.1076 microm was investigated using about 60 microwatts of cw narrowband radiation (Deltanu=50 kHz) generated by difference-frequency mixing in a periodically-poled Lithium Niobate crystal. A single frequency Ti:Sapphire laser (power 800 mW) and a monolithic diode-pumped Nd:YAG laser (300 mW) were used as pump and signal waves respectively. We used natural enriched xenon, which contains nine stable isotopes, two of which, 129Xe and 131Xe, exhibit a hyperfine structure owing to their nuclear spin. The small isotope displacements expected for this atom and the complex hyperfine structure of the odd isotopes make it difficult to fully resolve the recorded saturated-absorption spectra. In spite of this, we have been able to analyze the isolated 129Xe F''=5/2?F'=7/2 hyperfine component by means of first-derivative FM spectroscopy.

Pulsed optical parametric generation, amplification, and oscillation in monolithic periodically poled lithium niobate crystals

We conducted a series of passively Q-switched Nd:YAG laser pumped optical parametric generation, amplification, and oscillation experiments in monolithic periodically poled lithium niobate (PPLN) crystals. Double-pass optical parametric generation with an effective gain length of 10 cm in a PPLN crystal was performed in comparison with single-pass operation in the same crystal. By seeding a PPLN optical parametric amplifier with a distributed feedback (DFB) diode laser, we produced 200-ps transform-limited laser pulses at 1549.6 nm and observed parametric gain competition at different pump levels. For optical parametric oscillations, we first demonstrated 22% power efficiency from a 2.4-cm intrinsic-cavity PPLN optical parametric oscillator pumped by a 4.2-ns, 10-kW passively Q-switched Nd:YAG laser. Preliminary studies on DFB optical parametric oscillators in PPLN are mentioned. The temporal and spectral properties of these optical parametric generators, amplifiers, and oscillators are characterized and discussed.

Low-threshold, high-efficiency, high-repetition-rate optical parametric generator based on periodically poled LiNbO 3

We report a high-repetition-rate optical parametric generator (OPG) with a periodically poled lithium niobate (PPLN) crystal pumped by an acousto-optically Q-switched CW-diode-end-pumped Nd:YVO4 laser. For the maximum 1064nm pump power of 970mW, the maximum conversion efficiency is 32.9% under the conditions of 250 degrees C, 1064nm pulse repetition rate of 22.6kHz and pulse width of 12ns and the PPLN OPG threshold in the collinear case is less than 23.7?J. The output power increases with the increase of the crystal temperature. The 1485?1553nm signal wave and 3383?3754nm idler wave are obtained by changing the temperature and the angle of the PPLN crystal.

Tunable single-frequency ultraviolet generation from a continuous-wave Ti : sapphire laser with an intracavity PPLN frequency doubler

We report a single-longitudinal-mode continuous-wave Ti : sapphire ring laser that is intracavity frequency doubled in periodically poled lithium niobate (PPLN). Using a multi-grating PPLN crystal, the second harmonic is tunable from 386 to 403 nm – close to the PPLN ultraviolet absorption edge – with a maximum generated power of 114 mW. The wavelength dependence of the critical operating temperature required to eliminate photorefractive effects in the PPLN crystal is determined.

Topographic investigation of ferroelectric domain structures in periodically-poled lithium niobate crystals by a profilometer

A topographic investigation of periodically poled lithium niobate (PPLN) crystals was performed by recording a map of the crystal surface after a selective etching process using a standard profilometer. A procedure to correct for the systematic error introduced by the finite size of the tip is discussed in detail so that the width of ferroelectric domains can be mapped with an estimated tolerance of about 3% along the whole length of the sample. The method is applied to a PPLN structure obtained by the Czochralski off-center technique.