CsLiB6O10 Crystals Research Articles

High-peak-power picosecond deep-UV laser sources.

Ultrafast deep-UV laser sources have extensive applications across a wide number of fields, whether biomedicine, photolithography, industrial processing, or state-of-the-art scientific research. However, it has been challenging to obtain deep-UV laser sources with high conversion efficiency and output peak power. Here, we simultaneously demonstrated high-peak-power picosecond deep-UV laser sources at two typical wavebands of 263.2 and 210.5 nm via the efficient fourth- and fifth-harmonic generation. The highest peak power of 263.2 and 210.5 nm laser radiations were up to 2.13 GW (6.72 ps) and 1.38 GW (5.08 ps). The overall conversion efficiencies from the fundamental wave to the fourth and fifth harmonic were up to 42.9% and 28.8%, respectively. The demonstrated results represent the highest conversion efficiencies and output peak powers of picosecond deep-UV laser sources at present to our knowledge. Additionally, we also systematically characterized the deep-UV optical properties of typical birefringent and nonlinear borate crystals, including α-BaB2O4, β-BaB2O4, LiB3O5, and CsLiB6O10 crystals. The experiments and obtained numerous new optical data in this work will contribute to the generation of ultrahigh-peak-power deep-UV and vacuum-UV laser sources and crucial applications in both science and industry, such as high-energy-density physics, material science, and laser machining.

Minimization of the response time of a 20 W deep-ultraviolet light at 266 nm during intermittent operation

We demonstrated stable intermittent operation of a 266-nm picosecond pulsed light source with an average power of 20 W. The 266-nm beam, which had a maximum average power of 35.5 W, was generated by frequency conversion of a 1064-nm laser with an LiB3O5 crystal and a CsLiB6O10 (CLBO) crystal. The 1064-nm laser had a repetition rate of 600 kHz and an average power of 130 W and was capable of intermittent operation with an acousto-optic modulator in the fundamental laser section. By investigating the crystal temperature rise caused by the 266-nm light absorption in the CLBO crystal, we found that the crystal temperature rise caused by nonlinear absorption must be suppressed to achieve stable intermittent operation. The countermeasures allowed stable-intermittent operation at an average power of 20 W to be achieved, with a response time of 1.1 s for the 10%–90% rise conditions and a stability of 2%p-p for the average power fluctuation from 2 to 120 s. These results show that deep-ultraviolet picosecond pulses with an average power of 20 W can be used for industrial applications that require stable intermittent operation.

Growth of large and high quality CsLiB6O10 crystals from self-flux solutions for high resistance against UV laser-induced degradation

Crystal growth of CsLiB6O10 (CLBO) was conducted by using various self-flux solutions. We evaluated the degradation under 266 nm irradiation, with measured intensity of scattered green light. The CLBO crystal grown from Li-poor composition had the highest resistance to the laser UV-induced degradation compared with the other composition. In addition, the scattering of the green laser light was low. Furthermore, we also grew a larger CLBO crystal without cracks and inclusions from Li-poor flux composition using a larger crucible, which shows that this method is highly suitable for growing large and high quality CLBO crystals.

Growth of high-quality transparent SrB4O7 single crystals with high degradation resistance for DUV laser application

We grew borate crystals, SrB4O7 (SBO), by the top-seeded solution growth (TSSG) method. High-quality transparent SBO single crystals were successfully obtained from the stoichiometric melt by a seed cooling technique. The optical properties of the SBO crystals, which showed wide transparency, high transmittance, and high resistance to optical damage compared with synthetic silica glass and CsLiB6O10 (CLBO) crystals, were evaluated. Our results reveal for the first time that the SBO crystals exhibit outstanding degradation resistance at a DUV wavelength of 266 nm.

High-power and high-conversion efficiency deep ultraviolet (DUV) laser at 258 nm generation in the CsLiB6O10 (CLBO) crystal with a beam quality of M2

We report a 10kHz, 10.5W deep ultraviolet (DUV) laser at 258nm with a pulse duration of 3ns by fourth-harmonic generation (FHG) in a CsLiB6O10 crystal with high-conversion efficiency. The fundamental laser is at 1030nm with 35W output power consisting of a Yb:YAG ceramics thin rod amplifier. The M2 of the DUV laser was confirmed to be <1.5. To the best of our knowledge, this is the best beam quality for DUV laser power higher than 10W generated by FHG of a solid-state laser, as well as the highest conversion efficiency of 31% from infrared to DUV so far.

Highly efficient 355 nm UV generation with non-collinear phase-matching by a prism-coupled device based on CsLiB6O10

We report 355 nm third-harmonic generation (THG) of UV light using CsLiB6O10 (CLBO). To compensate for the walk-off angle in THG by Type II CLBO, we designed a prism-coupled device that takes advantage of non-collinear phase-matching. This new device, equipped with a Nd:YVO4 laser source, achieved THG with 1.86 W at 47.6% conversion efficiency from the second-harmonic input. This result marks a 1.43-fold improvement over a conventional CLBO crystal, thus validating the effectiveness of the design for walk-off compensation in Type II THG. This is also the first time THG has been achieved using CLBO.

Development of High-Quality Nonlinear Optical Crystal CsLiB6O10 and Its Application to High-Power Picosecond Deep-Ultraviolet Pulse Generation

Development of High-Quality Nonlinear Optical Crystal CsLiB6O10 and Its Application to High-Power Picosecond Deep-Ultraviolet Pulse Generation

Ultraviolet laser-induced degradation of CsLiB_6O_10 and β-BaB_2O_4

We investigated ultraviolet (UV) laser-induced degradation of nonlinear optical crystal CsLiB6O10 (CLBO) and β-BaB2O4 (BBO) using a high-repetition-rate pulsed laser. In this research, we found that the degradation of CLBO was caused by a UV-induced refractive index change at a peak power density higher than a few tens of MW/cm2. On the other hand, BBO exhibited lower UV transmittance at a higher intensity of 10 MW/cm2 and the UV absorption increased with time due to the formation of an absorption center. Moreover, we confirmed that the degradation resistance of CLBO with fewer light scattering defects was improved.

Temperature and frequency dependences of the electric properties of CLBO crystals

In this paper, CsLiB6O10 (CLBO) crystals were grown by top-seeded solution growth (TSSG) method using self-flux. The temperature and frequency dependences of the dielectric constant, dielectric loss, AC conductivity and impedance spectroscopy for different cuts CsLiB6O10 crystals were investigated, also temperature characteristics of the resonance frequency and electromechanical coupling were studied. The results show that (001)-plane of CsLiB6O10 crystal has the highest dielectric constant with a value of 109, highest AC conductivity and highest electromechanical coupling factor of about 17% at elevated temperature, these make CsLiB6O10 crystal excellent candidate for electrical application at elevated temperature. Also the anisotropy of electric properties has strong relationship with the crystal structure.

Growth and characterization of Al-doped CsLiB6O10 crystal

To improve the hygroscopic nature of cesium lithium borate (CsLiB6O10, CLBO), the aluminum (Al) doping of CLBO crystal was investigated. By using the top-seeded solution growth (TSSG) method with a [001] direction seed, an Al-doped CLBO crystal with the dimensions of 60×58×24mm3 was grown from the self-flux system. The influence of Al doping on crystal growth and various properties of CLBO was discussed. The growth rate of CLBO crystal along the c direction was reduced by Al doping. Compared with undoped CLBO, the optical homogeneity and transmittance of Al-doped CLBO had no obvious change, but the hygroscopic nature of Al-doped CLBO was improved.

Characterization of CsLiB6O10 Crystal Grown in a Dry Atmosphere

We grew CsLiB6O10 (CLBO) crystals in a dry atmosphere to obtain high-quality crystals that include less water as an impurity. We estimated the level of water impurity in the crystals using a nonpolarized Fourier transform infrared spectrometer and also measured bulk laser damage resistance using a 266 nm high-repetition-rate ultraviolet pulse laser. We found that the CLBO crystals grown in a dry atmosphere had an approximately 80% less water impurity and 1.2- to 1.5-fold greater resistance to laser damage than the CLBO crystals grown in an ambient atmosphere.

Effect of water impurity in CsLiB_6O_10 crystals on bulk laser-induced damage threshold and transmittance in the ultraviolet region

We investigate the effect of water impurity in a CsLiB(6)O(10) (CLBO) crystal on the ultraviolet properties of the bulk laser-induced damage threshold (LIDT) and transmittance. The water impurity was eliminated by heating the CLBO sample with dimensions of 5 mm x 5 mm x 10 mm at 150 degrees C in an ambient atmosphere and subsequently in a dry atmosphere. The bulk LIDT of the sample after heat treatment improved by about 1.6-fold compared with that before heat treatment.

Corneal ablation with new 193 nm solid-state laser: Preliminary experiments

To assess the ability of a newly developed 193 nm solid-state laser to ablate the cornea.Osaka University, Osaka, Japan.A prototype laser engine was developed by combining a 1547 nm laser diode, fiber amplifiers, and 5 stages of a frequency-conversion system using CsLiB6O10 crystals as the last stage. Poly(methyl methacrylate) (PMMA) plates were exposed to the prototype laser beam to determine the relationship between the fluence and ablation rate. Laser irradiation of porcine corneas was performed to induce morphological changes, and the quality of the lesions was determined by light and scanning electron microscopy.The relationship between the fluence and ablation rate of the 193 nm solid-state laser was comparable to that of the argon-fluoride excimer laser. Light and scanning electron microscopy of the porcine corneas showed that the linear and square lesions had sharp, clean edges.Smooth ablations of PMMA plates and porcine corneas were obtained by the laser. Further investigations must be conducted to determine whether this laser can be an alternative laser source for keratorefractive surgery.

Determination of the nonlinear optical coefficients of the Li_xCs_(1−x)B_3O_5 crystals

The nonlinear optical coefficients of LiB3O5 (LBO), CsB3O5 (CBO), and CsLiB6O10 (CLBO) crystals have been measured by both the Maker fringe technique and the phase-matching method. With the former technique the coefficients of LBO, CBO, and CLBO crystals have been determined relative to d36 (KDP) at the wavelength 1064.2 nm. The relative ratios of the dij coefficients measured by Maker fringe technique have been found to be in good agreement with those deduced by the phase-matching method.

28.4 W 266 nm ultraviolet-beam generation by fourth-harmonic generation of an all-solid-state laser

In this paper, 28.4W 266nm ultraviolet-beam generation by fourth-harmonic generation of an all-solid-state laser using a CsLiB6O10 crystal was reported. A conversion efficiency of 24.7% was obtained.

Generation of all-solid-state, high-power continuous-wave 213-nm light based on sum-frequency mixing in CsLiB6O10.

Achievement of more than 100 mW of pure continuous-wave deep-ultraviolet radiation at 213 nm has been demonstrated in an efficient all-solid-state laser system that uses two Brewster-cut CsLiB6O10 (CLBO) crystals. The first crystal is used for 266-nm generation by external resonant doubling of 532-nm radiation from a frequency-doubled Nd:YVO4 laser. Subsequent sum-frequency mixing is performed in a second CLBO crystal placed in a diode-pumped Nd:YAG laser cavity to mix the single-pass 266-nm output with circulating 1064-nm light.

Growth of High-Quality CsLiB6O10 Crystals from Materials Mixed in Aqueous Solution

CsLiB6O10 crystals were grown from high-quality sintered powder using the Top-Seeded Solution Growth (TSSG) method. The starting materials were prepared by calcination via a homogeneous precursor mixed in aqueous solution. The crystal grown possessed approximately a two-fold higher bulk ultraviolet laser-induced damage threshold than conventional crystals and fused quartz. The IR absorption intensity due to hydroxyl ions in the crystal was revealed to be almost the same as that in conventional crystals.

Generation of 5-W deep-UV continuous-wave radiation at 266 nm by an external cavity with a CsLiB6O10 crystal.

A Brewster-cut CsLiB6O10 crystal is employed as an external resonant frequency doubler to generate cw deep-UV radiation at 266 nm. We have generated 5.0 W of usable cw output power, which is 6.1 W in the crystal, for an incident green power of 9.6 W, corresponding to an internal conversion efficiency of 61.8%. The power obtained is, to our knowledge, three times higher than previously reported for cw 266-nm generation.

Electrooptic Effect in Non-Centrosymmetric CsLiB6O10 Borate Crystals

Electrooptic coefficient of CsLiB6O10 crystals has been experimentally determined as r63=3.3*10-12m/V. The half-wave voltage for CsLiB6O10 (Ul/2=26 kV) is three orders of magnitude larger than that of the known KDP crystals.

Ultrabroad-band phase matching in two recently grown nonlinear optical crystals for the generation of tunable ultrafast laser radiation by type-I noncollinear optical parametric amplification

It was found that the generation of ultrabroad-band femtosecond pulsed laser radiation is possible in two recently grown nonlinear optical crystals, K2Al2B2O7 (KABO) and CsLiB6O10 (CLBO), by employing a type-I noncollinear optical parametric amplification (NOPA) scheme, pumped by Ti:sapphire second harmonic (395 nm) radiation. The phase-matching bandwidths of the process are as large as 152 and 164 THz in KABO and CLBO crystals, with the values of the noncollinear angles (α) between pump input (considered monochromatic) and seed pulses input are 3.3° and 3.0°, respectively. The phase-matching bandwidth calculated for the same type-I NOPA in BBO crystal is 157 THz with α=3.7°. In addition to the large phase-matching bandwidth in CLBO, the major advantages of this crystal are that it can easily be grown to large sizes and it also has a higher threshold against laser damage. The most attractive properties of KABO crystal are that it is nonhygroscopic as well as mechanically robust and easy to cut and polish. Having moderate birefringence the angular and spectral bandwidths of both CLBO and KABO crystals are larger than that of BBO crystal and the deleterious walk-off angles are smaller than that of BBO. The walk-off angles at the pump wavelength of NOPA with CLBO, KABO, and BBO crystals are about 2.1°, 2.7°, and 4.0°, respectively. Here we present the nonlinear optical parametric properties of CLBO and KABO crystals for the generation of ultrabroad band femtosecond laser radiation by the NOPA technique, since we know of no such report so far in the literature.