PPLN Crystal Research Articles

Mid-infrared dual-comb spectroscopy with absolute frequency calibration using a passive optical reference.

We demonstrate an absolute-frequency-calibrated mid-infrared dual-comb spectrometer by using a reference absorption cell. The source is based on a singly-resonant OPO containing two MgO:PPLN crystals in a common ring cavity, synchronously pumped by two mode-locked Yb-fiber lasers. The repetition-rate of the two pumps are stabilized while their offset frequencies and the OPO cavity length are not actively controlled. The reference spectrum is used to correct the frequency fluctuations in the sample spectrum providing a high-quality averaged spectrum with spectral resolution of 6 GHz and calibration precision of 120 MHz, without adding any complexity to the experimental setup or signal processing.

The Effect of Thermal Effect of Magnesium Neodymium Double Doped Periodically Polarized Lithium Niobate on Self-Optical Parameter Oscillation

Based on the theory of thermal effect, the temperature rise, deformation and the deformation of periodically polarized region are simulated. The theory of nonlinear transformation, the effect of thermal effect on nonlinear effect is analyzed.Based on the oscillation theory of the laser resonator, the laser resonator was proposed to be constructed, and the influence of the laser resonator and the optical parametric oscillation was analyzed to describe the optical parametric oscillation process of Nd:MgO:PPLN crystal construction more accurately.The thermal effect of the original dynamic model of OPO in the inner cavity was modified to better reflect the actual situation of the compound self-optical parametric oscillator. The experimental study of the future self-optical parametric oscillator provided a design idea and laid a theoretical foundation for the subsequent experiments.

Generation of high-power 780 nm femtosecond pulses by an all-polarization-maintaining Er-doped fiber amplification system.

A 187fs pulse laser with 2.3W of output power at 1560nm is built for second-harmonic generation (SHG), which is the highest average power output reported from an all-polarization-maintaining single-mode Er-doped chirped pulse amplification system. By subsequently using an MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal as frequency doubler, a 183fs pulse laser with 1.1W output power at 778nm is generated. Benefitting from a polarization-stable fundamental laser input and the temperature control of the PPLN crystal, the power fluctuation of the frequency doubled laser is less than 0.5% during 24h. To the best of our knowledge, the 1.1W output at 780nm band is also the highest average power generated from a frequency doubled femtosecond Er-doped fiber laser.

Enhancement of efficiency in femtosecond optical parametric oscillators using group-velocity-matching in long nonlinear crystals

The authors describe the exploitation of group-velocity-matching in femtosecond optical parametric oscillators (OPOs) for enhanced down-conversion efficiency into the mid-infrared (mid-IR). We demonstrate the concept in a femtosecond OPO based on a long MgO:PPLN crystal, for the first time, by utilizing group-velocity-matching between pump and idler pulses. Taking advantage of the wide phase-matching bandwidth when pumped near 1 µm enables the use of a 42-mm-long crystal, resulting in an oscillation threshold as low as 5 mW, pump depletion of 78%, and an idler quantum conversion efficiency up to 48% into the mid-IR. Using 80–100 fs pump pulses tunable across 997–1070 nm, we have generated idler radiation across 3132–4273 nm (2340–3193 cm−1) with spectral bandwidth of 140–180 nm, providing up to 65 mW of average power at 80 MHz repetition rate. The near-IR signal is tunable across 1392–1568 nm, with up to 76 mW of average power in transform-limited pulses of ∼400–600 fs duration without dispersion compensation. Preferential operation at group-velocity-matched wavelengths leads to intrinsically high passive power stability with <1% rms fluctuation over 1 h for both signal and idler. With the capability for rapid pump tuning in the mid-IR, this OPO represents a viable source for spectroscopic applications, which we demonstrate using CH4 gas. Extension to other quasi-phase-matched nonlinear crystals is also discussed.

RF intensity modulated mid-IR light source based on dual-frequency optical parametric oscillation.

Laser detection and ranging (Ladar)-radar uses intensity-modulated laser beam for ranging and remote sensing. It has the advantages of high spatial resolution from Ladar and immunity to atmospheric turbulence from radar, since the synthetic wavelength is in the order of meters. Intensity modulated mid-IR laser can extend the Ladar-radar concept to mid-IR spectrum. An intensity modulated mid-IR light source with tunable wavelength and modulation frequency is presented. A dual-frequency 1064 nm laser is used to pump an optical parametric oscillator with magnesium oxide doped periodically-poled lithium niobate crystal (MgO:PPLN) as the nonlinear medium. The beat note frequency of the dual-frequency pump laser can be tuned from 140 to 160 MHz. When the pump power is 13 W, the idler output power at mid-IR is 2.38 W, corresponding to a pump-idler conversion efficiency of 19.4%. The wavelength of the idler light is tuned from 3.1 to 3.8 μm by changing the temperature of the MgO:PPLN crystal. The modulation spectra of the mid-IR light are studied. The frequency stability of the beat note in mid-IR is compared with the one in the pump, which are 4.1 Hz and 3 Hz in 240 second measuring time, respectively.

Intracavity sum-frequency generation of a 795 nm pulsed laser with a short pulse width based on two MgO : PPLN crystals

We report a 795 nm tunable pulsed laser with intracavity sum-frequency generation (SFG) based on an optical parametric oscillator (OPO) pumped by a 1064 nm laser. The cavity consists of two periodically poled MgO : PPLN crystals, the periods of which are 22.0 and 31.0 μm. The crystal with the period of 31.0 μm is used to generate a mid-IR beam, while the other crystal is used for SFG of the pump beam and the mid-IR beam. The pulsed width of the 795 nm laser is 3.6 ns, and the repetition rate of the laser is 35.3 kHz. The peak power of the laser is 2.8 kW with a linewidth of 0.35 nm. The 795 nm laser threshold pump power is 1.4 W and the optical-to-optical efficiency of 1064 nm to 795 nm is 5.7% at a maximum output power. The laser is supposed to be a kind of a competitive near-IR laser source for studying a diode-pumped rubidium laser.

Double-pass high-efficiency sum-frequency generation of a broadband orange laser in a single MgO:PPLN crystal

A high-efficiency broadband orange laser is demonstrated by use of double-pass sum-frequency mixing in a step-chirped MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal (ᴧ = 10.1-10.4 µm). The temperature-gradient technique is used to enhance the bandwidth of the output spectrum. A maximum orange output power of 129 mW (~65% conversion efficiency) was achieved at room temperature operation, and up to ~7.2 nm bandwidth at a temperature difference of 20 ᵒC was realized. This scheme presents an attractive approach for the generation of high power and broadband short-wavelength lasers from a single crystal, which may extend the potential biomedical and spectroscopic applications.

Maskless Arrayed Nanofiber Mats by Bipolar Pyroelectrospinning.

The numerous advantages of micro- and nanostructures produced by electrospinning (ES) have stimulated enormous interest in this technology with potential application in several fields. However, ES still has some limitations in controlling the geometrical arrangement of the fiber mats so that expensive and time-consuming technologies are usually employed for producing ordered geometries. Here we present a technique that we call "bipolar pyroelectrospinning" (b-PES) for generating ordered arrays of fiber mats in a direct manner by using the bipolar pyroelectric field produced by a periodically poled lithium niobate crystal (PPLN). The b-PES is free from expensive electrodes, nozzles, and masks because it makes use simply of the structured pyroelectric field produced by the PPLN crystal used as collector. The results show clearly the reliability of the technique in producing a wide variety of arrayed fiber mats that could find application in bioengineering or many other fields. Preliminary results of live cells patterning under controlled geometrical constraints is also reported and discussed in order to show potential exploitation as a scaffold in tissue engineering.

1514 nm eye-safe passively Q-switched self-optical parametric oscillator based on Nd3+-doped MgO:PPLN

We examined a 1514 nm eye-safe passively Q-switched self-optical parametric oscillator. The nonlinear crystal is an a-cut Nd:MgO:PPLN crystal, and the size of the crystal was 6 mm × 2 mm × 30 mm with 0.4 at.% Nd3+ doped and a grating period of 29.8 μm. When the crystal absorbed 12.8 W, the output maximum single-pulse energy reached 39 μJ, and a pulse width of 6.1 ns at a repetition rate of 5.4 kHz was obtained. The peak power was 6 kW, giving a slope efficiency of 42%.

Compact V-Type Cavity for Harmonically Pumped 1-GHz Femtosecond Optical Parametric Oscillator

In this letter, we propose and demonstrate a practically compact 1-GHz repetition-rate femtosecond optical parametric oscillator (OPO) based on MgO:PPLN crystal, which is harmonically pumped by a 53 MHz Yb-doped fiber laser. The multiplication of the repetition rate is derived by placing the nonlinear crystal in a miniaturized V-type cavity with 13.9 cm length. The near-infrared signal output pulses are tunable from 1350 nm to 1650 nm. The signal pulse duration across the complete tuning range is measured to be around 125 fs. Thanks to the high repetition rate, broadband tenability, and simplicity of the optical setup, this type of OPO holds promise for many applications.

Simultaneous Second-Harmonic, Sum-Frequency Generation and Stimulated Raman Scattering in MgO:PPLN.

In this study, simultaneous second-harmonic generation (SHG), sum frequency generation (SFG), and Raman conversion based on MgO-doped periodically poled lithium niobate (MgO:PPLN) for multi-wavelength generation is demonstrated. The approach used is based on a single MgO:PPLN crystal poled with a uniform period of 10.2 µm that phase matches SHG and SFG, simultaneously. Using a simplified double-pass geometry, up to 0.8 W of blue light at 487 nm is achieved by a frequency-doubling 974 nm laser diode pump, and 0.5 W of orange light at 598 nm is generated by frequency mixing 974 nm pump with C-band (1527–1565 nm) tunable laser source. At high pump powers of the 974 nm laser source, other unexpected peaks at 437, 536, 756, 815 and 1038 nm were observed, of which the 1038 nm line is due to Stimulated Raman Scattering within the MgO:PPLN crystal. The resulting multi-wavelength light source may find a wide range of applications in biomedicine and basic research.

Tunable 3 µm optical vortex parametric oscillator

We propose a tunable millijoule-level 3-µm vortex laser formed with a 1-µm ns vortex pulse-pumped quasi-phase matching MgO-doped periodically poled lithium niobate (MgO:PPLN) optical parametric oscillator with a singly resonant plane-parallel cavity configuration. The wavelength of the vortex output is tuned within the range of 3.360–3.677 µm merely by controlling the temperature of the MgO:PPLN crystal. The maximum vortex output energy of 2.14 mJ is obtained at the maximum pump energy of 21 mJ, and corresponds to an optical to optical conversion efficiency of 10.2% and a photon conversion efficiency of 33.5%. The handedness of the vortex output is controlled just by inverting the handedness of the pump vortex beam.

Continuous-Wave Widely Tunable MgO:PPLN Optical Parametric Oscillator With Compact Linear Cavity

An efficient continuous-wave, widely tunable, intra-cavity optical parametric oscillator (OPO) based on periodically poled MgO:LiNbO3 (MgO:PPLN) with a compact three-mirror linear cavity was demonstrated. The mode radii of fundamental and OPO cavities with plane and concave mirrors were calculated and theoretically compared. The result shows that the fundamental laser beam could be compressed, and its power density on the MgO:PPLN crystal could be improved by optimizing concave radii of cavity mirrors. Meanwhile, better mode matching between fundamental cavity and OPO cavity could be realized. A widely tunable signal spectrum from 1.43 to $1.79~\mu \text{m}$ and an idler spectrum from 2.62 to $4.16~\mu \text{m}$ were achieved as the OPO system derived by a diode laser end-pumped Nd:YVO4 crystal laser at 1064 nm. The maximum total output power up to 6.35 W (signal output power of about 4.24 W at $1.60~\mu \text{m}$ and idler output power of about 2.11 W at $3.17~\mu \text{m}$ ) and conversion efficiency of 31.6% were obtained at an incident pump power of 20.1 W.

Parametric generation in a PPLN crystal pumped by a Q-switched mode-locked Nd : YAG laser: comparison of the superluminescent and singly resonant operation regimes

The output characteristics of light in two parametric generation regimes [parametric superluminescence and parametric generation in a singly resonant optical parametric oscillator (OPO) based on a 50-mm long PPLN crystal, synchronously pumped by a 50-ps Nd : YAG laser] are compared. The total average output power at the wavelengths of signal (λ = 1475 nm) and idler (λ = 3820 nm) waves in the superluminescence regime is ∼120 mW (peak power ∼120 kW). The maximum total conversion efficiency with respect to the absorbed power in the superluminescence regime is ∼60%. The maximum conversion efficiency into the idler wave with respect to the absorbed pump power is 15% and 25% (quantum efficiencies of 54% and 90%) for the superluminescence and singly resonant OPO regimes, respectively. The maximum values of the average output power at the idler wavelength are ∼30 and ∼60 mW at degrees of pump depletion of 47% and 55% for the superluminescence and singly resonant OPO regimes, respectively.

Generation of narrow-band single-photon states via spontaneous parametric down-conversion for quantum memories in doped crystals

We present experimental results on the generation of narrow-band single-photon states via cavity-enhanced spontaneous parametric down-conversion in a PPLN crystal and demonstrate the feasibility of conditional preparation of single 867-nm photons with a 70-MHz linewidth, compatible with optical quantum memory devices based on Nd3+-doped isototopically pure Y7LiF4 crystals.

Theoretical study on thermal characteristic of MgO: PPLN crystal in high power optical parametric oscillator

This study focuses on the thermal characteristic of an end-pumped MgO: PPLN crystal by solving the transient temperature evolution model in a high power optical parametric oscillator. In this model, an approach based on contact mechanics theory is proposed to quantitatively calculate the heat transfer between rough contacting surfaces of crystal and heat sink. Based on the model, a parametric study has been performed to investigate the influence of the heat sink property, pump laserand crystal dimension on the thermal characteristic of the laser crystal. Obtained results reveal a closed correlation between the mentioned parameters and the thermal characteristic of the crystal indicating that a proper selection of the parameters is essential to control the crystal temperature and improve the performance of the laser.

Efficient intra-cavity continuous-wave periodically poled lithium niobate-doped MgO optical parametric oscillator with compact V-type cavity

A compact efficient intra-cavity singly resonant optical parametric oscillator (OPO) based on periodically poled lithium niobate-doped MgO (MgO:PPLN) was investigated. A concave–concave fundamental cavity was used for focusing the fundamental beam waist on MgO:PPLN crystal, which enables more compact setup and less insertion loss than traditional insertion of a focusing lens. Two V-type OPO cavities with single and double outputs were used for comparison with idler light outputting from one and both end mirrors, respectively. The results show that the double outputs configuration achieved higher output power for its advantage of reducing the reversed OPO process and diffraction loss of the idler light. Under an incident pump power of 12.4 W, a maximum signal output power of 2.89 W at 1549 nm and total idler output power of 1.44 W at 3394 nm were obtained with a total conversion efficiency up to 34.9%.

High-Power Single-Frequency Source in the Mid-Infrared Using a Singly Resonant Optical Parametric Oscillator Pumped by Yb-Fiber Laser

We present a high-power single-frequency continuously tunable mid-infrared (MIR) singly resonant optical parametric oscillator (SRO) using $\text{80-mm}$ -long MgO-doped PPLN (MgO:PPLN) crystal pumped by a continuous-wave Yb-fiber laser. The SRO having four-mirror ring-cavity configuration is tunable in the MIR band of $\text{3761--3970 nm}$ yielding a maximum power of $\text{2W}$ at $\text{3895 nm}$ when incident pump power is $\approx \text{16 W}$ . Due to strong phonon–polariton coupling in MgO:PPLN crystal, the intracavity signal-beam spectrum exhibits multiple peaks depicting stimulated polariton scattering. By replacing one of the cavity mirrors with a $\text{5}\%$ outcoupler, the stimulated polariton modes are suppressed as a consequence of additional cavity losses. Along with a tunable signal extending from $\text{1453}$ to $\text{1484 nm}$ , we obtained the maximum signal power of $\approx \text{4W}$ at $\text{1464 nm}$ at the maximum pump power of $\approx \text{16W}$ . In addition, we have measured the frequency and power stability of the outcoupled signal and idler beams over long as well as short durations. The improvement in beam quality of idler was discernible when the intracavity signal was outcoupled, which is essentially a consequence of reduced thermal load on MgO:PPLN crystal.

Broadening of the sum-frequency phase-matching bandwidth by temperature gradient in MgO:PPLN.

We demonstrate bandwidth broadening in cascaded MgO-doped periodically poled lithium niobate (MgO:PPLN) crystals (Λ=10.3 μm) using the temperature-gradient technique. Up to 2.8nm bandwidth at 600nm spectral region is achieved using two 50mm long cascaded MgO:PPLN crystals via sum frequency generation. This technique combines the merits of high conversion efficiency attributed to cascaded nonlinearity and the reconfigurability of temperature-gradient-induced chirp for broadening of the input wavelength acceptance range.

Superluminescent high-efficient parametric generation in PPLN crystal with pumping by a Q-switched mode locked Nd:YAG laser

We present results on parametric superluminescence in a periodically poled lithium niobate crystal pumped by a train of 45 ps pulses using a Q-switched mode locked Nd:YAG laser. The conversion efficiency (with respect to the absorbed power) was ~83%. To the best of our knowledge, this is the highest efficiency obtained with powerful superluminescent parametric sources. At the average pumping power of the laser of ~0.5 W and repetition rates of 1 and 1.7 kHz, the peak total output powers were as high as 210 and 200 kW, and the powers of the idler wavelength (3.82 µm) were 55 and 50 kW. New lines in the visible and UV spectrum were observed and are explained. The experiments demonstrated that the spectral and angular characteristics of superluminescence are determined by the pumping laser. In particular, the line width of the signal wave was close to that of the pumping line at ~200 GHz, and the divergence of the signal and idler waves depended only on the convergence (divergence) angle of the pumping radiation (30 mrad) and was independent of the wavelength.