BIBO Crystal Research Articles

The influence of spin-orbit coupling on the electronic structure and optical properties of α-BiB3O6 crystals: a first-principles investigation

The α-BiB3O6 (BIBO) crystal is highly regarded in the field of nonlinear optical (NLO) due to its excellent ultraviolet (UV) NLO properties, including a short ultraviolet cutoff edge (270 nm), appropriate birefringence (Δn = 0.175@546 nm), and strong second harmonic generation (deff = 3.20 pm V−1). In this study, the first-principles computational software PWmat was employed to conduct theoretical calculations on BIBO crystals, including the non-negligible spin-orbit coupling (SOC) effects induced by the presence of the heavy element bismuth (Bi). The results show that after the inclusion of the SOC, the calculated birefringence (0.173@546 nm) and effective second harmonic generation (SHG) coefficient (deff = 3.16 pm V−1) are in good agreement with experimental data. Furthermore, comparative analysis has demonstrated that the changes in the band structure induced by the SOC effect are significant factors influencing the optical properties of the material.

London Dispersion Effects on the Structure and Properties of Nonlinear Optical BiB3O6 Crystal.

α-BiB3O6 (BiBO) is an important nonlinear optical (NLO) material with high efficiency for applications in harmonic generations and quantum technology. Owing to its low symmetry and cooperative Bi3+ lone pair arrangement, it has also exceptional large piezoelectric and electro-optic coefficients and strong anisotropies on other material characteristics. Previous theoretical calculations on its physical (mainly optical) properties often gave confusing results. It is found here that London dispersion (LD) tends to stabilize structures with closer pack entities like lone pair heavy ion Bi3+ with large polarizabilities, which is ignored in most previous density functional theory (DFT) calculations. Present study shows that without considering the LD effect, the structure of α-BiB3O6 (BiBO) was predicted with an over-estimated (by over 10 %) unique b-axis while underestimates a and overestimates c in a less amount. Consequently it is not possible to use the calculated structure to obtain meaningful properties of this important material. By applying a modified post-DFT LD correction based on linear combination of atomic orbitals (LCAO) and B3LYP functional, the experimental structure is well reproduced with the theoretical optimized one. Many important material property tensors of BiBO crystal are calculated in unprecedented precisions, including: dielectric constants (static and in THz range), elastic and elasto-optic constants, piezoelectric constants, refractive indices, NLO and electro-optic (EO) coefficients. Among them, theoretical calculation of the refractive indices in the THz range by diagonalizing the clamped-ion dielectric constants was firstly achieved at least for BiBO crystal. The calculation also confirms that BiBO has an exceptional large piezoelectric constant d22=40 pC/N and largest free EO coefficients , , on the order of 10 pm/V among borate crystals. The calculation also reveals that the large free EO coefficients are largely originated from the piezoelectric induced photo-elastic effect and for practical high speed applications only the clamped-ion EO coefficients take effect. The clamped ion EO coefficient of =-4.17 pm/V, =-2.61 pm/V are obtained for the first time and may be consulted if one seeks to design BiBO crystal as a high-speed EO modulator. Furthermore, full tensor matrix of the elasto-optic constants was obtained on the first time. Together with the calculated elastic constants, it can help to design acoustic optic modulating devices with preferable figure of merits 10 times that of traditional quartz crystal.

Efficient single-cycle mid-infrared femtosecond laser pulse generation by spectrally temporally cascaded optical parametric amplification with pump energy recycling.

We proposed spectrally temporally cascaded optical parametric amplification (STOPA) using pump energy recycling to simultaneously increase spectral bandwidth and conversion efficiency in optical parametric amplification (OPA). Using BiB3O6 and KTiOAsO4 nonlinear crystals, near-single-cycle mid-infrared (MIR) pulses with maximum energy conversion efficiencies exceeding 25% were obtained in simulations. We successfully demonstrated sub-two-cycle, CEP-stable pulse generation at 1.8 µm using a four-step STOPA system in the experiment. This method provides a solution to solve the limitations of the gain bandwidth of nonlinear crystals and the low conversion efficiency in broadband OPA systems, which is helpful for intense attosecond pulse generation and strong laser field physics studies.

Harnessing nonlinear frequency upconversion of Talbot effect with flexible Talbot lengths

We report on a simple experimental scheme demonstrating nonlinear frequency upconversion of the Talbot effect with controllable Talbot lengths at high conversion efficiency. Using a microlens array (MLA) as an array illuminator at 1064 nm onto a 1.2-mm-thick BiBO crystal, we have observed the second harmonic Talbot effect in green at 532 nm with a Talbot length twice that of the pump Talbot length. However, the Talbot length is constant for fixed parameters of the periodic object and the laser wavelength. With the formulation of a suitable theoretical framework, we have implemented a generic experimental scheme based on the Fourier transformation technique to independently control the Talbot lengths of the MLA in both the pump and the second harmonic, overcoming the stringent dependence of MLA parameters on the self-images. Deploying the current technique, we have been able to tune the Talbot lengths from z T = 26 cm to z T = 62.4 cm in the pump and z T = 12.4 cm to z T = 30.8 cm in the second harmonic, respectively. The single pass conversion efficiency of the Talbot images is 2.91% W−1, an enhancement of a factor of 106 as compared to the previous reports. This generic experimental scheme can be used to generate long-range self-images of periodic structures and also to program desired Talbot planes at required positions at both pump and upconverted frequency to avoid any mechanical constraints of experiments.

Temperature-Dependent Optical Properties of Bismuth Triborate Crystal in the Terahertz Range: Simulation of Terahertz Generation by Collinear Three-Wave Mixing in the Main Crystal Planes

Terahertz (THz) frequency generation via nonlinear optical techniques is of particular interest due to the immense potential of this type of radiation in various scientific fields, ranging from medicine to telecommunications. Selecting suitable nonlinear media for laser frequency down-conversion presents a challenging task. Considering an approach that uses nonlinear crystals with high radiation resistance, pumped by intense laser pulses near their damage threshold, we suggest the crystal of bismuth triborate (BiB3O6, BIBO). Compared to other borate-class crystals, BIBO exhibits relatively high coefficients of quadratic susceptibility. In this paper, we have studied the optical properties of BIBO samples in a wide spectral range from 0.1 to 2.1 THz at temperatures of 473, 383, 295, and 77 K using Terahertz Time-Domain Spectroscopy (THz-TDS). Furthermore, we simulated collinear three-wave interactions with nonzero efficiency for difference frequency generation (DFG) in the THz range. For the pump wavelengths of about 800 nm, we determined phase-matching (PM) conditions and compared the generation efficiency for different crystal cuts. The potential of utilizing BIBO crystal for terahertz frequency generation is discussed.

Role of large Rashba spin-orbit coupling in second-order nonlinear optical effects of polar BiB3O6

The $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{BiB}}_{3}{\mathrm{O}}_{6}$ (BIBO) is a widely used nonlinear optical (NLO) crystal in ultraviolet (UV) energy region. Although the spin-orbit coupling (SOC) effect on the band structure of BIBO has been investigated, the role of SOC effect on the second-order NLO properties is still unclear. In this article, using the first-principles calculations, we discover the unusual polar lone-pair electron can induce large Rashba SOC effect in the electronic structure of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{BiB}}_{3}{\mathrm{O}}_{6}$ (BIBO), which can fundamentally change its NLO responses around the band edge. For the second harmonic generation (SHG), it is found that the inclusion of SOC effect can significantly improve the accuracy of SHG coefficients calculations in BIBO, closer to the experimentally measured values. Importantly, we also find the large Rashba SOC effect can strongly modulate the photodriven high-order charge/spin currents in BIBO, giving rise to large bulk photovoltaic effect, large circular photogalvanic effect, and an unusual spin photocurrent effect. Interestingly, the roles of SOC in tuning the charge and spin currents are quite different. Accordingly, we propose the spin current switching around the band edge induced by the large Rashba SOC in a BIBO crystal. Our study not only provides a deep and complete understanding on the unique roles of Rashba SOC effect in the second-order NLO properties of BIBO, but also suggests the BIBO crystal may be used for UV-range spintronics and optoelectronics.

100-mJ class, sub-two-cycle, carrier-envelope phase-stable dual-chirped optical parametric amplification.

Based on dual-chirped optical parametric amplification (DC-OPA) and type-I BiB3O6 (BiBO) crystals, the generation of >100 mJ, 10.4 fs, 10 Hz, carrier-envelope phase (CEP)-stable laser pulses, which are centered at 1.7 µm, was demonstrated producing a peak power of 10 TW. CEP-dependent high harmonic generation (HHG) was implemented to confirm the sub-two-cycle pulse duration and CEP stabilization of infrared (IR) laser pulses. As far as we know, the obtained pulse energy and peak power represented the highest values for sub-two-cycle CEP-stable IR optical parametric amplification. Additionally, the prospects of achieving high-energy water window isolated attosecond pulses (IAPs) via our developed laser source were discussed.

A 515-nm laser-pumped idler-resonant femtosecond BiB3O6 optical parametric oscillator

We report on an idler-resonant femtosecond optical parametrical oscillator (OPO) based on BiB3O6 (BiBO) crystal, synchronously pumped by a frequency-doubled, mode-locked Yb:KGW laser at 515 nm. The idler wavelengths of OPO can be tuned from 1100 nm to 1540 nm. At a repetition rate of 75.5 MHz, the OPO generates as much as 400 mW of idler power with 3.1 W of pump power, the corresponding pulse duration is 80 fs, which is 1.04 times of Fourier transform-limited (FTL) pulse duration at 1305 nm. In addition, the OPO exhibits excellent beam quality with M 2 < 1.8 at 1150 nm. To the best of our knowledge, this is the first idler-resonant femtosecond OPO pumped by 515 nm.

Millimetre-wave range optical properties of BIBO

We present the thorough studies of optical properties of BiB3O6 (BIBO) crystal in the millimeter-wave (subterahertz) range. We observe a large birefringence Δn = nZ -nX = 1.5 and the values of absorption coefficients of all three axes to be less than 0.5 cm−1 at the frequency of 0.3 THz. The difference from visible range in angle ϕ between the dielectric axis z and crystallophysical axis X is found to be more than 6°. The simulated phase-matching curves in the xz plane of the crystal show the optimal value of the angle θ to be around 25.5°±1° for an efficient millimeter-wave generation under the pump of 1064 nm laser radiation.

Efficient second-harmonic and terahertz generation from single BiB3O6crystal using nanosecond and femtosecond lasers.

The paper reports the efficient UV and terahertz generation from a 1.29 mm thick and Type I, θ=28.9∘ cut BiB3O6 (bismuth triborate, BIBO) crystal using femtosecond and nanoseconds laser pulses. We have employed 800 nm wavelength pulses of 50 and 140 fs obtained from a Ti:sapphire laser amplifier and oscillators at 1 kHz and 80 MHz repetition rates, respectively. The conversion efficiency of second-harmonic generation (SHG) was ∼50% while that obtained for terahertz (THz) generations was of the order of 1.85×10-5%. In addition, LDS-698 dye laser radiation tunable between 650-700 nm was also used as a source for SHG between the 325-350 nm range. The dye laser was pumped by SHG (532 nm) radiation from an electro-optically Q-switched Nd:YAG laser having a pulse repetition rate of 10 Hz and a pulse width of 10 ns. A conversion efficiency of 4.01% was obtained for generation of UV at 343.5 nm. Finally, we have measured the transmission, refractive index, absorbance, and conductivity properties of BIBO crystal in the THz domain. We also ascertained the coherence length, relative permittivity and reflectivity of the crystal.

Nd:GdVO4/Yb:YAG Intracavity Sum-Frequency CW Blue Laser Operating at 484 nm

We study a continuous-wave sum-frequency blue laser operating at 484 nm. The laser elaborated is based on the intracavity pumping technology. A 912 nm laser produced by an end-pumped Nd:GdVO4 crystal, using an 808 nm fiber-coupled laser diode, is employed to pump an Yb:YAG crystal in the cavity to achieve the simultaneous oscillations in 912 and 1030 nm lasers. An intracavity sum-frequency achieved in a type-I phase-matched BIBO crystal is used to obtain the 484 nm blue laser output. In our experiment, we apply a linear coaxial laser resonator structure. As a result, we obtain a sumfrequency blue laser output of 317 mW at a pump power of 25 W. The slope efficiency of the designed laser is 2.8%, and the beam quality factors are 1.34 in the X direction and 1.36 in the Y direction, respectively, with the power fluctuations about 3.8% within four hours.

Green-Yellow-Orange-Red Spectral Range with Sum-Frequency Generation Using BIBO Crystal Pumped with an Optical Parametric Amplifier

In this letter, we show the broadband sum-frequency generation (SFG) in the Green-Yellow-Orange-Red spectral range using bismuth triborate, BiB3O6 crystal (BIBO) as a nonlinear material. We perform a noncollinear phase-matching configuration within the BIBO crystal using the remaining light behind the second harmonic generation stage and the infrared idler of an optical parametric amplifier (OPA). The obtained mixing radiation of ultrafast light sources to generate femtosecond pulses across the 520.5 to 742.5 nm region is observed. The SFG spectrum from a single-pass cross-correlation intensity over such visible range is shown. The SFG wavelengths as a function of the tunable wavelength idler OPA agree with the expectations of the parametric conversion condition and open the door to practical multi-beam or multi-color sum-frequency generators.

Study of saturated-absorption resonances on the 3P0, 1, 2 – 3D1, 2, 3 transitions of magnesium atoms in a hollow-cathode discharge cell

The saturated-absorption resonances on the 3P0, 1, 2 – 3D1, 2, 3 transitions of magnesium atoms in a hollow-cathode discharge cell are studied. The line width (FWHM) for the observed saturated-absorption resonance on the 33P0 → 33D1 transition turns out to be ∼220 MHz. Experiments are performed using a system based on a 766-nm diode laser with amplification and frequency doubling in a nonlinear BiBO crystal. The results obtained are of interest for sub-Doppler cooling on the 33P2 → 33D3 transition.

Crystal-Configuration Considerations for Higher-Sensitivity Picosecond-Pulse SHG FROG

We experimentally compare a thick BIBO crystal, a walk-off compensating configuration of thin BBO crystals, and a thin PPLN crystal for the use as a nonlinear medium in SHG FROG, aiming for increased sensitivity required for complete pulse characterization of low-energy (below pJ) pulses a few picoseconds long at wavelengths near 1030 nm. We investigate the dependence of the spectral bandwidth of the frequency-doubled input ultrashort pulse and the conversion efficiency on focal-spot size in the nonlinear crystal. Both numerical and experimental results confirm an increase of the bandwidth with tighter focusing in a thick BIBO and a more-than-threefold increase of conversion efficiency compared to a thin BIBO crystal. A PPLN crystal is found to be the most efficient among the three, but very thin (<; 0.3 mm) crystals would be required to extend the measurement capabilities of SHG FROG to sub-ps pulses. A SHG FROG using a PPLN crystal for characterization of picosecond pulse is demonstrated with a sensitivity of 2 ×10 -3 (mW)2.

515 nm pumped femtosecond optical parametric oscillator at 755 MHz based on BiB3O6

We report a high-power femtosecond optical parametric oscillator (OPO) based on BiB3O6 crystal with a repetition rate of 755 MHz, which is 10 times that of the pump laser. With 3.75 W pump power from a 90 fs frequency-doubled mode-locked Yb:KGW oscillator, the OPO can provide signal pulses tunable over a spectral range from 693 to 1000 nm and idler pulses tunable from 1100 to 2000 nm. The maximum signal output power is 1.34 W centered at 746 nm and the corresponding idler output power is 0.408 W at 1663 nm. Laser pulse as short as 67 fs is obtained at the central wavelength of 722 nm. This work is promising for a variety of applications in optical communications and pump-probe spectroscopy.

Controlled generation of array beams of higher order orbital angular momentum and study of their frequency-doubling characteristics

We report on a simple and compact experimental scheme to generate high-power, ultrafast, higher-order vortex-array beams. Simply by using a dielectric microlens-array (MLA) and a plano-convex lens, we have generated array-beams carrying the spatial property of the input beam. Considering the MLA as a 2D sinusoidal phase-grating, we have numerically calculated the intensity pattern of the array-beams in close agreement with the experimental results. Using vortex beams of order as high as l = 6, we have generated vortex array-beam with individual vortices of orders up to l = 6. We have also theoretically derived the parameters controlling the intensity pattern, size, and the array-pitch and verified experimentally. The single-pass frequency-doubling of vortex-array at 1064 nm in a 1.2 mm long BiBO crystal produced green vortex-array of order, lsh = 12, twice the order of pump beam. Using lenses of different focal lengths, we have observed the vortex-arrays of all orders to follow a focusing dependent conversion similar to the Gaussian beam. The maximum power of the green vortex-array is measured to be 138 mW at a single-pass efficiency as high as ~3.65%. This generic experimental scheme can be used to generate the array beams of desired spatial intensity profile across a wide wavelength range by simply changing the spatial profile of the input beam.

Tunable, high-repetition-rate, dual-signal-wavelength femtosecond optical parametric oscillator based on BiB3O6

We have demonstrated a high-repetition-rate tunable femtosecond dual-signal-wavelength optical parametric oscillator (OPO) based on BiB3O6 (BiBO) crystal, synchronously pumped by a frequency-doubled mode-locked Yb:KGW laser. The cavity is simple since no dispersion compensators are used in the cavity. The wavelength range of dual-signal is widely tunable from 710 to 1000 nm. Tuning is accomplished by rotating phase-matching angle of BiBO, and optimizing cavity length and output coupler. Using a 3.75 W pump laser, the maximum average dual-signal output power is 760 mW at 707 and 750 nm, leading to a conversion efficiency of 20.3% not taking into account the idler power. Our experimental results show a non-critical phase-matching configuration pumped by a high peak power laser source. The operation of the dual-signal benefits from the balance of phase matching and group velocity mismatching between the two signals.

Octave-spanning energy-scalable CEP-stabilized pulses from a dual-chirped noncollinear optical parametric amplifier

A dual-chirped noncollinear optical parametric amplification scheme exploiting the unique dispersion properties of BiB3O6 (BiBO) crystal is proposed. Passively CEP-stabilized 2-μm pulses from a broadband pumped OPA are efficiently amplified via noncollinear phase-matching in a thin BiBO crystal, resulting in an octave-spanning spectrum that supports a transform limited duration of 10.1 fs. The proposed scheme shows excellent compressibility and high energy scalability for the output signal. Sub-two-cycle CEP-stable mid-IR pulse with energy exceeding 20 mJ can be expected, which is potentially a perfect driving source in attosecond and strong-field researches.

Generation of octave-spanning mid-infrared pulses from cascaded second-order nonlinear processes in a single crystal

We report on experimental generation of a 6.8 μJ laser pulse spanning from 1.8 to 4.2 μm from cascaded second-order nonlinear processes in a 0.4-mm BiB3O6 (BIBO) crystal. The nonlinear processes are initiated by intra-pulse difference frequency generation (DFG) using spectrally broadened Ti:Sapphire spectrum, followed by optical parametric amplification (OPA) of the DFG pulse. The highest energy, 12.6 μJ, is achieved in a 0.8-mm BIBO crystal with a spectrum spanning from 1.8 to 3.5 μm. Such cascaded nonlinear processes are enabled by the broadband pump and the coincident phase matching angle of DFG and OPA. The spectrum is initiated from the DFG process and is thus expected to have passive stable carrier-envelope phase, which can be used to seed either a chirped pulse amplifier (CPA) or an optical parametric chirped pulse amplifier (OPCPA) for achieving high-energy few-cycle mid-infrared pulses. Such cascaded second-order nonlinear processes can be found in many other crystals such as KTA, which can extend wavelengths further into mid-infrared. We achieved a 0.8 μJ laser pulse spanning from 2.2 to 5.0 μm in KTA.

Polarized Raman spectroscopy of delta‐BiB3O6 at 7–350 K

BiB3O6 crystal has been characterized by Raman spectroscopy. Polarized low‐frequency spectra have been obtained. Temperature measurements have been carried out in range 7–350 K. Raman spectra have been numerically simulated with lady software package. The results of experiment confirmed the contribution of the Bi3+ ions and BO4 groups in nonlinear optical properties of BiB3O6. The studied crystal is a promising medium for up‐ and down‐Raman laser‐frequency converters. Copyright © 2017 John Wiley &amp; Sons, Ltd.