Fourth Harmonic Generation Of Nd Research Articles

Growth and characterizations of a new nonlinear optical crystal for 266 nm laser generation: LiSr3Be3B3O9F4

The LiSr3Be3B3O9F4 (LSBBF) single crystal with dimensions of 30 × 20 × 15 mm3 was grown from a LiF-NaBF4-B2O3-SrF2 flux system using a top-seeded solution growth method with a seed perpendicular to the (011) plane. The X-ray rocking curve, transmission spectra, refractive indices and laser-induced damage threshold have also been studied. The Sellmeier equations were derived from the measured refractive indices for the first time. According to the Sellmeier equations, the limits of type-I and type-II phase-matching (PM) frequency doubling wavelengths are 241 and 318 nm, respectively. It indicates that LSBBF is a potential UV nonlinear optical crystal for the fourth harmonic generation of Nd:YAG laser at 266 nm.

Large aperture and non-critical phase-matched fourth harmonic generation of Nd:Glass lasers

A fourth harmonic generation (FHG) scheme in focusing beams is proposed and demonstrated for large aperture Nd:glass laser facilities. By placing the focusing lens before the FHG crystal, the problem of ultraviolet damage can be overcome, largely without affecting FHG conversion efficiency owing to the large angular acceptance of the non-critical phase matching technique. A numerical simulation of the FHG process indicates that angular acceptance can be appropriately increased by lowering the working temperature and jointing the two adjacent compensating angles, so that FHG in focusing beams with relatively small F numbers becomes feasible. With a 170 mm × 170 mm × 7 mm and 65% deuterated potassium dihydrogen phosphate crystal mounted in a high-precision, temperature-controlled system, high-efficiency FHG has been demonstrated in the focusing beam with a full beam convergence angle of 36 mrad. When driven with a 223 J, second harmonic radiation (2ω), 1 ns flat-top pulse with a beam area of 130 cm2, corresponding to 1.7 GW/cm2 2ω input intensity, 182 J of fourth harmonic radiation (4ω) were generated.

High-power ultraviolet 278-nm laser from fourth-harmonic generation of an Nd:YAG amplifier in CsB3O5 crystal**Project supported by the National Natural Science Foundation Program of China (Grant Nos. 11504389 and 61505226), the National Key Research Development Program of China (Grant Nos. 2016YFB040203 and 61535013), and the National Development Project for Major Scientific Research Facility of China (Grant No. ZDYZ2012-2).

We report on the experimental investigation and theoretical analysis of a nanosecond pulse high power ultraviolet (UV) 278 nm laser by fourth-harmonic generation (FHG) of a 1112-nm Nd:YAG amplifier in LiB3O5 (LBO) and CsB3O5 (CBO) crystals. The UV laser delivers a maximum average power of 10.3 W at 278 nm with peak power of 36.8 kW under input pump power of 41 W at 556 nm. This is, to the best of our knowledge, the highest output power at the specific UV wavelength of 278 nm. We also performed the theoretical investigation on the FHG with a model in the Gaussian approximation of both spatial and temporal profiles, especially accounting for the two-photon absorption effect in CBO crystal for the first time. The average output power, pulse width, and beam spatial distribution of the UV laser were simulated. The theoretical calculations are in close agreement with the experimental results.

Structure and Optical Properties of K0.67Rb1.33Al2B2O7 Crystal

A UV nonlinear optical (NLO) crystal K0.67Rb1.33Al2B2O7 (KRABO) has been obtained by the top-seeded solution growth method for the first time. Its structure is formed of coplanar [BO3]3− triangle groups and [Al2O7]8− groups, which are built from two [AlO4]5− tetrahedra sharing one vertex. Rb and K atoms have the same coordinates and locate between each layer in a disorderly fashion. The crystal has a larger NLO effect compared with its analog K2Al2B2O7 (KABO), as evidenced by powder second harmonic generation (SHG) test. The shortest SHG phase-matching wavelength is down to 231 nm according to the first-principle calculation, which indicates that KRABO is possible for the fourth harmonic generation of Nd:YAG at 266 nm.

Secondary atomization of small hydrocarbon droplet by fourth harmonic generation of Nd:YAG pulsed laser

Atomization of small fuel droplets using a UV laser is considered experimentally under atmospheric conditions. The droplet diameters in the experiments are 30µm, 20µm, and 15µm. The maximum spatial resolution is 232nm/pixel. The temporal resolution is 100ns. The fuels under test are diesel oil (JIS K2204, No. 1), hexadecane (99.5%) and o-Xylene (98%). A Nd:YAG pulse laser operating at 266nm is used in the experiments. The maximum laser energy is 10mJ. The laser beam diameter is 5mm, and the flash time is 7ns. As a result, the diesel oil droplets of all diameters are atomized using 10mJ of laser energy. The 15-µm-diameter hexadecane droplets are not atomized. The laser energy threshold for atomization of the 30-µm-diameter o-Xylene droplets is 4.5mJ, and the calculated laser intensity is 450J/m2 under the assumption of a Gaussian distribution. The atomization delay time is almost 8µs. Moisture is observed just before atomization occurs. The moisture indicates that this phenomenon can be explained based on the heat transfer process of the laser energy.

Noncritically phase-matched fourth-harmonic generation of Nd:glass lasers and design of final optics assembly

The noncritically phase-matched (NCPM) fourth-harmonic generation (FHG) with partially deuterated dihydrogen phosphate (KD*P) crystal at an Nd:glass laser radiation wavelength of 1053.1nm has been confirmed. NCPM FHG has been achieved in 70% and 65% deuterated KD*P crystal at the temperature of 17.7°C and 29.3°C, respectively. The angular acceptance of 70% and 65% deuterated KD*P crystals fixed at their NCPM temperature were measured, which were 53 and 55mrad, respectively. The application of the NCPM FHG in a high-power laser facility for inertial confinement fusion is also discussed. Based on the theoretical analysis, the NCPM KD*P can be placed after the focus lens; thus, the laser-induced damage of a fused-silica lens at ultraviolet can be avoided.

Noncritically phase-matched fourth harmonic generation of Nd:glass lasers in partially deuterated KDP crystals

Noncritically phase-matched (NCPM) fourth harmonic generation (FHG) of Nd:glass laser radiation in partially deuterated dihydrogen phosphate (KD*P) crystals has been demonstrated. At an Nd:glass laser wavelength of 1053.0 nm, NCPM FHG is achieved in 70% deuterated KD*P at a crystal temperature of 18.5±0.1 °C. Tuning the fundamental laser wavelength from 1052.9 to 1053.2 nm, FHG in KD*P is NCPM by changing the crystal temperature from 17.9 °C to 20.5 °C. When driven with 2.4 J of second harmonic radiation in a 3 ns flat-top pulse, corresponding to 1 GW/cm(2) 2ω drive intensity, 1.9 J of fourth harmonic radiation was generated in a 6 mm long KD*P crystal, yielding a second to fourth harmonic energy conversion efficiency of 79%.

Crystal growth and optical properties of non-UV absorption K2Al2B2O7 crystals

In this paper, large and transparent K2Al2B2O7 (KABO) crystals were grown using NaF as a flux in a non-oxygen atmosphere for the first time. Through optimization of the growth condition, bulk KABO crystal has been obtained with good quality. The transmittance spectrum shows that the abnormal UV absorption from 200 to 300nm of KABO crystals could be effectively eliminated by this new method. The non-UV absorption KABO crystal is promising for the application of fourth harmonic generation of Nd:YAG lasers. A 280mW average output power was obtained through fourth harmonic generation of Nd:YAG laser with 10kHz, 10ns pulse and a 8.85-mm-thick KABO crystal. The conversion efficiency up to 33.4% of second harmonic generation from 532 to 266nm has also been achieved with a 25ps, 10Hz laser system and the same crystal. To our knowledge, this is the highest result at present.

YAl 3(BO 3) 4: Crystal growth and characterization

The growth and characterization of YAl 3(BO 3) 4 (YAB), a potential nonlinear optical crystal for the fourth harmonic generation of Nd:YAG laser, was reported. Using top-seeded solution growth method, a YAB crystal with the dimensions of 16×16×18 mm 3 was obtained from B 2O 3–Li 2O flux system. The advantages of this flux system and the growth process were discussed in detail. The as-grown YAB crystal was verified by powder X-ray diffraction. The transparency spectra indicated that the cut-off edge of the as-grown YAB was 170 nm. The fourth harmonic generation of a frequency doubled Nd:YAG laser, from 532 to 266 nm, was carried out with a YAB crystal doubler for the first time. Output pulse power obtained was 2.4 mW at 266 nm and the conversion efficiency from 532 to 266 nm was about 15.6%.

パルスレーザー堆積法により作製したＺｎＯ系透明導電膜の特性改善

Approximately 200-nm-thick 1.5 wt.% Al-doped zinc oxide (AZO: 1.5 wt.% Al2O3) films have been deposited on glass substrates at 100°C by pulsed laser deposition (PLD) using the fourth harmonic generation (FHG) of Nd: YAG laser (λ=266 nm). In order to reduce resistivity of as-deposited films, annealing process was carried out by ArF excimer laser with laser energy density of 34 mJ/cm2. As a result, the value of resistivity was not almost improved: 1.54×10-3 Ω•cm (for as-deposited) and 1.33×10-3 Ω•cm (for annealed). On the other hand, for the films annealed by fourth harmonic generation of Nd:YAG laser with laser energy density of 20 mJ/cm2, the value of resistivity was reduced from 1.36×10-3 Ω•cm to 8.34×10-4 Ω•cm.

Type-I walk-off compensated second and fourth harmonic generation ofNd:YAG laser radiation from a Li2B4O7 crystal

A type-I walk-off compensation (WOC) arrangement has been made forthe second harmonic generation (SHG) and the fourth harmonic generation (FOHG)of commercially available Q-switched Nd:YAG laser radiation, for the firsttime, using two identically cut Li2B4O7 crystals. The enhancement ofthe conversion efficiencies has been realized in the WOC arrangement by afactor of 2.71 for the SHG and 2.65 for the FOHG relative to thedouble-crystal non-walk-off arrangement. The absolute values of the conversionefficiencies obtained for WOC SHG and FOHG are 3.52% and 3.56% respectively,applying input power densities for the fundamental and second harmonic of theNd:YAG laser beam at only 28.3 MW cm-2 and 11.7 MW cm-2, respectively.

Nd:YAGレーザーの高出力第4高調波発生

We have analyzed the relation between the conversion efficiency of CLBO crystal for fourth-harmonic generation of Nd:YAG laser and the effect of frequency-conversion parameters such as peak intensity, crystal length, and so on. We have found that the conversion efficiency of CLBO crystal is interrelated with the product of input average intensity and crystal length. It has been theoretically confirmed for the first time that this interrelation is caused by the thermal dephasing. By use of this theoretical examination, we have generated 20.5-W UV output power by fourth-harmonic generation of Nd:YAG laser in a CLBO crystal. This value is, to our knowledge, the highest UV power generated in all-solid-state lasers.