Lithium Triborate Research Articles

Synthesis and thermoluminescence characterization of either Cu- or Ag-doped lithium triborate

Lithium Triborate (LiB3O5 or LTB), is characterized by chemical stability and good mechanical properties, and it has an effective atomic number (Zeff = 7.39) close to that of the human tissue (Zeff = 7.42), making it a potential dosimeter. The objective of this research is to examine the Thermoluminescence (TL) features and dosimetric characteristics of both Cu-doped and Ag-doped LTB. The material was synthesized using the solid-state synthesis method and four different dopant levels were used for each element (0.1%, 0.5%, 1%, 3%); various techniques such as X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy were used for structural and compositional characterization, for samples annealed at 500 °C for 1 h in all cases. Specific TL features were studied, such as TL glow curve shape, sensitization and sensitivity, fading behavior as well as kinetic characterization using two supplementary techniques, namely fractional glow technique and deconvolution analysis. The effect of each dopant element is different in the (same) lithium triborate matrix in terms of sensitivity. TL dosimetric peaks are yielded for both dopant elements; however, the optimum doping level is 3% for Ag but just 0.1% for Cu. Furthermore, the samples were irradiated at different doses, ranging from 0.5 to 2048 Gy, in order to study the corresponding dose response. A remarkable dose response linearity was observed for the main dosimetric peak of both materials, ranging up to ∼1 kGy.The fading results suggest that LTB doped with 0.1% Cu is the most promising material for dosimetric applications.

Generation and Evaluation of an Efficient Femtosecond Green Laser.

We demonstrate femtosecond ultra-stable green laser generation by an ytterbium-doped polarization-maintaining fiber laser with a 2.4 mm long lithium triborate (LBO) crystal. We generated 5.6 W of femtosecond green light at 520 nm for a fundamental power of 12 W, which corresponds to a conversion efficiency of 46.7%. The fiber chirped-pulse amplifier, which has an environmentally immune front end, delivered 170 fs pulses at a 75 MHz repetition rate centered at 1040 nm. According to the dispersion of the optical material in a double-frequency setup, the introduced dispersion had a negligible effect for the green laser, and the pulse duration of the generated green laser was calculated to be 171 fs, resulting in an excellent power stability, with fluctuation as low as 0.16% of the generated green light. This system could be of great interest in ultrafast optical and photobiology research.

Continuous-Wave Self-Raman Vanadate Lasers Generating Versatile Visible Wavelengths

In this review, the developments of efficient high-power CW orange-lime-green lasers by using intracavity stimulated Raman Scattering (SRS) in Nd-doped vanadate lasers are systematically discussed. The overall properties of the spontaneous Raman spectra in Nd:YVO4 and Nd:GdVO4 crystals are overviewed. The critical phase matchings of using the lithium triborate (LBO) crystals for sum frequency generation (SFG) and second harmonic generation (SHG) are thoroughly reviewed. We make a detailed review for achieving the individual green-lime-orange emissions from the self-Raman Nd:YVO4 and Nd:GdVO4 lasers with LBO crystals. The following is to review the dual-wavelength operations of the lime-green and orange-green lasers. Finally, the procedure for generating the triple-wavelength operation of orange-lime-green simultaneous emissions is completely described. The present review is expected to be useful for developing compact, efficient, high-power CW visible lasers for applications including medical treatment, biology, spectroscopy, and remote sensing.

Spatial shaping of low- and high-order harmonics generated using vortex beams

We demonstrate the generation of the low- and high-order harmonic vortex beams from a single spiral phase plate illuminated by different laser wavelengths. The second harmonic (532 nm) originates from the application of the wavefront-structured 1064 nm femtosecond pulses with fractional orbital angular momentum (OAM) during propagation through a lithium triborate crystal, while the third harmonic (500 nm) originates from the application of the wavefront-structured near-IR (1500 nm) femtosecond pulses with integer OAM during propagation through a 150 μm thick fused silica plate. The topological charges (TCs) of the second and third harmonics are measured and compared. The increase in TC and the peculiarities in OAM variations during modification of the polarisation of the incident radiation are analysed and discussed. The two-colour-pump-driven second-harmonic vortex radiation interacted with an Ar gas jet to generate vortex harmonics up to the 14th order with double-lobe complex spatial profiles in the extreme ultraviolet region.

Highly efficient continuous-wave solid-state Raman crystal lasers at 555 and 559 nm

High-power efficient continuous-wave Nd:YVO4/KGW Raman lasers at 555 and 559 nm are achieved by using a double-sided dichroic coating output coupler to improve the resonance quality factor. The Np-cut potassium gadolinium tungstate (KGW) is used to generate the Stokes waves at 1159 and 1177 nm by placing the polarization of the1064 nm fundamental wave parallel to the Ng and Nm axes, respectively. The lithium triborate (LBO) crystal with the cut angle in the XY plane for the type-I phase matching is used to perform the intracavity sum frequency generation for yielding the green light at 555 nm and the lime light at 559 nm at the optimal phase matching temperature. Experimental results were systematically accomplished to comprehend the optimal cavity length for the conversion efficiency. Under the optimal cavity length, the output powers can reach 6.6 and 6.3 W at a pump power of 22 W for the wavelengths of 555 and 559 nm, respectively. The conversion efficiencies can be up to 30% and 28.6% for 555 and 559 nm, respectively.

Compact efficient high-power continuous-wave Nd:YVO4/KGW/LBO Raman lasers for selectable wavelengths within 559-603 nm

Compact efficient high-power continuous-wave Nd:YVO4 Raman lasers for selectable wavelengths within 559-603 nm are achieved by using KGW crystal for intracavity stimulated Raman scattering (SRS) and lithium triborate (LBO) crystal for intracavity sum frequency generation (SFG) and second harmonic generation (SHG). The LBO crystal with the cut angle in the XY plane for the type-I phase matching is used to perform intracavity SHG or SFG. Experimental results reveal that the participated Stokes lines include the internal vibration mode at 901 cm-1, the external vibrational mode at 209 cm-1, and the combination mode of the 901 cm-1 and 209 cm-1 Raman shifts. By tuning LBO temperature for attaining the maximum output power, the output spectrum reveals the triple peaks of 588.7, 595.7, and 603.1 nm with the intensity ratio of 10:4:1. Under this circumstance, the output power can reach the highest value of 10.8 W at a pump power of 40 W. Furthermore, the output spectrum can be simply concentrated on the single peaks among 588.7 (orange), 565.7 (yellow), and 559.1 nm (lime) by tuning LBO temperature to fulfill the selection of the critical phase matching. The output powers at a pump power of 40 W can be up to 8.0, 6.1, and 9.8 W for the single-peak emission at 588.7, 565.7, and 559.1 nm, respectively. Finally, a dual-peak emission of 565.7 and 572.3 nm with total output power of 5.2 W can be generated by tuning LBO temperature to match the SFG for 572.3 nm.

Effect of gamma-irradiation on the photoluminescence of silver-doped lithium triborate glass.

Optical-luminescence properties, including absorption spectra, photoluminescence excitation spectra, and changes in photoluminescence spectra after irradiation with γ-rays in the dose range of 1-3Gy, were measured for novel L i B 3 O 5:A g dosimeter glass. A clear dependence of the intensity of the photoluminescence (PL), with a maximum of approximately 300nm, on the dose value when excited by light with λ e x c =220n m was observed. The mechanism of PL in γ-irradiated L i B 3 O 5:A g glass is proposed to be a consequence of radiation annihilation with the emission of relaxed exciton-like electronic excitations with the participation of impurity defects (A g 0) in the glass structure. Considering that L i B 3 O 5 has an effective atomic number of Z e f f =7.39, which is the closest to Z e f f =7.42 of human body tissue, L i B 3 O 5:A g glass can be very promising for γ-dosimetry in medical practice during radiation therapy of patients with cancer. The presence of lithium Li(6) and boron B(10) isotopes increases the sensitivity of L i B 3 O 5:A g glass to neutrons, which is promising for the manufacture of individual neutron dosimeters for applications in a new field of radiation therapy-neutron therapy.

Experimental demonstration on 400 nm-scale bandwidth optical parametric chirped-pulse amplification based on mixed cascaded crystals.

We present an optical parametric chirped-pulse amplification (OPCPA) based on mixed cascaded crystals, taking advantage of the unique parametric phase-matching of lithium triborate (LiB3O5, LBO) and yttrium calcium oxyborate ((YCa4O(BO3)3, YCOB) crystals. The OPCPA properties of LBO at 880 nm and YCOB at 750 nm are studied respectively. After amplification by two LBO and two YCOB crystals, a total signal gain of 108 and spectral bandwidth close to 400 nm is obtained. After accurate dispersion compensation with a grating-pair compressor and chirped mirror compensator, a pulse duration of 9.4 fs is obtained by a SHG-frequency-resolved optical grating (FROG). This approach will be of great significance in high energy amplifier for high peak power few-cycle laser sources.

A 172 mJ, high-energy picosecond 355 nm ultraviolet laser system at 100 Hz

Abstract A high-energy picosecond 355 nm ultraviolet (UV) laser operating at 100 Hz was demonstrated. A 352 mJ, 69 ps, 1064 nm laser at 100 Hz was realized firstly by cascaded regenerative, laser diode end-pumped single-pass and side-pumped main amplifiers. The stimulated Raman scattering-based beam shaping technique, thermally induced birefringence compensation and 4f spatial filter-image relaying systems were used to maintain a relatively homogeneous beam intensity distribution during the amplification process. By using lithium triborate crystals for second- and third-harmonic generation (THG), a 172 mJ, approximately 56 ps, 355 nm UV laser was achieved with a THG conversion efficiency of 49%. To the best of our knowledge, it is the highest pulse energy of a picosecond 355 nm UV laser so far. The beam quality factor ${M}^2$ and pulse energy stability were ${M}_x^2$ =3.92, ${M}_y^2$ =3.71 and root mean square of 1.48%@3 hours. This laser system could play significant roles in applications including photoconductive switch excitation, laser drilling and laser micro-fabrication.

Auto-pump-depleted stable single-longitudinal-mode 1.5 μm source with the assistance of SHG.

To realize a stable single-longitudinal-mode (SLM) 1550-nm light source for the generation of non-classical states, a ring auto-pump-depleted singly resonant optical parametric oscillator (SRO) with the assistance of second-harmonic-wave generation (SHG) is designed and built in this Letter. A magnesium oxide doped periodically polarized lithium niobate (MgO:PPLN) crystal and a lithium triborate (LBO) crystal are employed as the optical parametric downconversion (OPDC) and SHG crystals, respectively. Especially, the introduced SHG can firstly increase the loss difference between the lasing and non-lasing modes so that the dual-mode or multi-mode coupling in the achieved SRO can be effectively eliminated and the stable SLM operation is achieved. At the same time, the SHG will automatically adjust the output coupling efficiency of SRO, so as to achieve efficient conversion efficiency and auto-pump depletion of SRO. In addition, due to the SHG, it is easy to achieve the low-intensity noise multi-wavelength output for the stable SLM SRO. As a result, the output powers of the SLM 1550 nm and 775 nm are up to 4.05 W and 3.25 W, respectively, and the total optical conversion of the built SRO can achieve 45.58%. The presented method paves a way to develop a compact stable SLM multi-wavelength SRO, and the obtained SRO is further beneficial to develop compact continuous-variable non-classical light fields.

The femtosecond structure of extreme contrast, multi-terawatt second-harmonic laser pulses at 400 nm

Ultrahigh intensity contrast and short pulse laser–solid interactions offer an attractive platform for investigating high-energy-density matter, particularly in the context of structured and ultra-thin targets that form hot, dense plasma conditions. Harmonic generation can improve the contrast of laser pulses by several orders of magnitude. In this study, we present the characterization of extreme contrast, relativistic intensity second-harmonic pulses at 400 nm, using the self-diffraction frequency-resolved optical gating technique. The 400 nm pulses were generated at various input intensities using potassium dihydrogen phosphate and lithium triborate crystals. Our observations reveal the presence of spectral broadening, pulse compression, and complex structures at higher input intensities. We see that extreme contrast, few tens of femtosecond pulses can have multiple “prepulses” at the 100s femtosecond scale as large as ten percent of the peak value. These can preionize a solid significantly and may influence the interaction. Simulations based on nonlinear pulse propagation equations reinforce our findings.

Efficient Continuous-Wave Eye-Safe Nd:GdVO4/KGW Raman Laser and Sum Frequency Generation for Deep-Red Emission

A concise, efficient continuous-wave eye-safe Nd:GdVO4/KGW Raman laser at 1525 nm is here demonstrated. A Nd:GdVO4 crystal was used to produce the fundamental field at 1341 nm and a KGW crystal generated the intracavity Stokes field at 1525 nm via wavelength conversion of stimulated Raman scattering. The output power of the Stokes field at 1525 nm could achieve 2.1 W under the pump power of 30 W. Furthermore, two different lithium triborate (LBO) crystals with critical phase matching were exploited to obtain deep-red emission at 714 nm via the intracavity sum frequency generation of 1341 and 1525 nm waves. One cutting angle was in the XY plane and the other was in the XZ plane. The empirical thermo-optical coefficients for the LBO crystal were exploited to systematically analyze the critical phase matching conditions. Numerical results revealed that the type-I phase matching angle in the XY plane was near θ = 90° and ϕ = 3.3° at room temperature, whereas the type-I phase matching angle in the XZ plane was near θ = 86.3° and ϕ = 0° at a temperature around 47 °C. The numerical values for the optimal temperatures for the two different cutting angles were found to be in good agreement with experimental results. At the pump power of 30 W, the output power at 714 nm was approximately 2.9 W by using the LBO crystal with the cutting angle in the XY plane. On the other hand, the maximum output power at 714 nm could be up to 3.2 W under the pump power of 30 W by using the cutting angle in the XZ plane. Furthermore, the linewidth of the SFG emission was confirmed to be nearly the same for the two different cutting angles. The overall linewidth could be narrower than 0.2 nm. The developed laser at 714 nm can be useful in the exploration of ionic and atomic radium isotopes with laser spectroscopy.

RF oscillator circuit for absorption coefficient measurement of piezoelectric materials.

We have introduced an approach for low optical absorption coefficient measurement of piezoelectric materials based on the piezoelectric resonance laser calorimetry (PRLC) method. An RF oscillator circuit provides a convenient way to track the piezoelectric resonance frequency during laser irradiation. In this work, the optical absorption coefficient of lithium triborate crystal under high-power IR laser irradiation was measured using the oscillator circuit and the conventional PRLC technique.

Frequency-doubled Q-switched 4 × 4 multicore fiber laser system.

Frequency doubling of a Q-switched Yb-doped rod-type 4 × 4 multicore fiber (MCF) laser system is reported. A second harmonic generation (SHG) efficiency of up to 52% was achieved with type I non-critically phase-matched lithium triborate (LBO), with a total SHG pulse energy of up to 17 mJ obtained at 1 kHz repetition rate. The dense parallel arrangement of amplifying cores into a shared pump cladding enables a significant increase in the energy capacity of active fibers. The frequency-doubled MCF architecture is compatible with high-repetition-rate and high-average-power operation and may provide an efficient alternative to bulk solid-state systems as pump sources for high-energy titanium-doped sapphire lasers.

Frequency-Doubled High-Power Optical Vortex Beam With Sub 500 fs Pulse Duration

We report on the generation of high-power ultrashort-pulsed optical vortex beams (VBs) with orbital angular momentum (OAM) of +1 in the infrared (IR) and +2 in the visible (VIS) spectral regions. The IR vortex beam was created from a Gaussian beam by employing a nanograting (S-waveplate) mode converter. With this approach we obtained an average power of up to 802 W at a wavelength of λ = 1030 nm in the IR-VB with a pulse energy of 802 µJ, a pulse duration of 460 fs, and a mode-conversion efficiency of 90.1%. By subsequent second harmonic generation, the IR-VB was frequency-doubled inside a lithium triborate (LiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> ) crystal. An average power of up to 320 W at λ = 515 nm was generated, with 320 µJ of pulse energy, 382 fs of pulse duration, and an IR-VB to SH-VB conversion efficiency of 39.9%. The generated IR and VIS VBs were characterized by a Mach-Zehnder type interferometric measurement, confirming the helical wavefronts at these high average powers. These results show that it is possible to efficiently generate high-quality VBs at multi hundreds of watts and confirm the OAM scaling law in harmonic generation processes.

Optical rotation in the lithium triborate nonlinear crystal

A dual-wavelength polarimetric technique at 633 and 661 nm has been used for the characterization of a nonlinear lithium triborate (LiB3O5) nonenantiomorphous biaxial crystal. The mismatch of the crystallographic and optical coordinate systems was taken into account. The optical rotatory power for light propagation along one of the optical axes is ρ = 7.06° mm−1. The gyration tensor component along the bisector between the x and y crystallographic axes has been measured as g 12 = 4.31 × 10−5. Computed values based on the crystalline structure and electronic polarizabilities are in good agreement with those obtained experimentally.

Design of High Energy Single Longitudinal Mode 355 nm UV Laser

355 nm laser is a widely applied light source, of which the two features mostly used are the damaging effect and propagation characteristic in the atmosphere. Thus, higher laser energy has always been required to perform better damage and provide further propagation range. We demonstrate high energy single longitudinal ultraviolet (UV) laser using a nonlinear optical crystal of lithium triborate (LBO) cut at θ=90° and φ= 37° with sizes of 10 mm × 10 mm × 30 mm in type I phase-matching, the source light from a single longitudinal mode (SLG) inject master oscillator power amplifier (MOPA) operated at a repetition rate of 5 Hz with a pulse duration of 10 ns. The maximum output energy of 0.308 J of 355 nm UV laser was reached through a total pump energy of 1.82 J 1064 nm and 532 nm laser with an nonlinear conversion efficiency of 16.9%. The experimental results prove that the LBO crystal is a reliable candidate for high-energy UV laser generation. The output high energy 355 nm laser has great application potential in material processing, microchip manufacturing and remote sensing.

Kilowatt-class high-energy frequency conversion to 95 J at 10 Hz at 515 nm

Abstract We report on frequency doubling of high-energy, high repetition rate ns pulses from a cryogenically gas cooled multi-slab ytterbium-doped yttrium aluminum garnet laser system, Bivoj/DiPOLE, using a type-I phase matched lithium triborate crystal. We achieved conversion to 515 nm with energy of 95 J at repetition rate of 10 Hz and conversion efficiency of 79%. High conversion efficiency was achieved due to successful depolarization compensation of the fundamental input beam.

Features of noncollinear second harmonic generation by infrared laser pulses with opposite frequency chirps

The features of noncollinear second harmonic generation during the interaction of broadband laser pulses with opposite frequency chirps are considered. The impact of spectral phase mismatch of the interacting pulses on spectrum width and the efficiency of conversion to the noncollinear second harmonic is analyzed on an example of lithium triborate and beta-barium borate crystals.

Precise measurements of the low optical absorption coefficients of massive lithium triborate crystal boules with untreated facets formed during the growth process.

A spatial diagnostic of optical quality of the massive lithium triborate crystal boule with untreated facets was performed by measuring optical absorption coefficients at 1070 and 1908nm wavelengths using the piezoelectric resonance laser calorimetry technique.