LBO Crystal Research Articles

High power widely tunable frequency-doubled 490 nm blue semiconductor disk laser

This paper presents a high power widely tunable frequency-doubled semiconductor disk laser emitting at 490 nm wavelength. The laser utilizes a specially designed gain chip with widened gain spectrum at the center wavelength of 980 nm, along with an anti-resonant microcavity, to extend the tuning range of the wavelength. A type-I phase-matched 5 mm length LBO crystal is used as the nonlinear crystal, and a fused quartz birefringent filter (BRF) is introduced to polarize the fundamental emission and narrow the linewidth of the laser. When the thickness of the used BRF is 1 mm, 50.7 nm tuning range of the 980 nm infrared laser is performed. A maximum output power of 5.36 W of the frequency-doubled 490 nm blue laser is achieved, and the optical-to-optical conversion efficiency from absorbed pump power to the blue light is about 15.3%. Meanwhile, a record tuning range of 21.5 nm of the blue laser is realized. The measured M2 factors of the blue laser are 1.00 in the x-direction and 1.04 in the y-direction, respectively.

Dual-wavelength solid-state Raman laser at 555 and 579.5 nm for spectrophotometric determination of carboxyhemoglobin

For accurate measurement of carboxyhemoglobin level in the blood, a compact dual-wavelength laser at 555 and 579.5 nm with conversion efficiency up to 27.5% is originally developed by using Nd:YVO4/KGW/LBO laser with intracavity stimulated Raman scattering (SRS), second harmonic generation (SHG), and sum frequency generation (SFG). The SRS material is an Np-cut KGW crystal to produce the Stokes wave at 1159 nm from the fundamental wave at 1064 nm. The SHG of the Stokes wave and the SFG of the Stokes and fundamental waves are efficiently achieved by employing two LBO crystals. The temperature of the first LBO crystal is steadily fixed at the optimal phase-matching for generating the output power at 579.5 nm, whereas the temperature of the second one is varied to manipulate the power ratio between the yellow and green emissions. At the balanced temperature of the second LBO crystal, the output powers of the yellow and green emissions can simultaneously reach 5.5 W at a pump power of 40 W.

Second harmonic generation of focused beams on the LFEX laser facility

There is a strong demand for efficient second harmonic generation (SHG) in ultra-intense short-pulse lasers. This paper demonstrates the generation of an unconverted fundamental (1ω)+second harmonics (2ω) mixed laser on the LFEX laser system. The experimental setup utilizes 0.5 mm-thick LBO crystal plates in a focusing beams implemented after an off-axis parabola, the design reduces the size and cost of the SHG system. The LFEX laser beams with four-beams combined energy of 222 J and a pulse duration of 1.5 ps, is successfully converted to 102 J of 2ω light and 100 J of unconverted 1ω light, 20 J is lost through surface reflections, and they are mixed at the focal point. Verification of successful SHG is confirmed through X-ray pinhole imaging and electron spectrometry. This novel technique is not limited to LFEX lasers and holds applicability for various ultra-intense lasers. Consequently, this accomplishment significantly contributes to expanding the capability for high-energy density laser-plasma experiments.

RMS error analysis of spatial uniformity and energy stability of the laser beam in second harmonic generation

The coupling of the energy stability and spatial uniformity of the laser beam before and after second harmonic generation (SHG) was analyzed. SHG experiments were performed using a Nd:YAG nanosecond laser and LBO crystals, and images, pulse shapes, and energies were measured. The relationship between energy stability and spatial uniformity uses a formula derived from the previous study to analyze changes in energy stability and spatial uniformity of the input beam and converted beam. In addition, the measured input beam shape and energy are compared with the results of applying the SHG converting equation considering pump depletion. Both methods were similar to the experimental results when corrected by empirical factors. Through SHG, it was confirmed that there is an optimal point of energy stability and spatial uniformity of the laser beam near the critical power.

Power scaling of intra-cavity Nd:YAG/LBO laser at 532 nm by birefringence compensation

We report an effective method to reduce the impact of polarization state changes caused by thermal birefringence in intra-cavity frequency-doubled laser. The laser consists of a diode side pumped Nd:YAG module, an acousto-optic modulator Q-switch, and an LBO crystal used for SHG generation in 532 nm laser. The effect of thermal birefringence originated by the Nd:YAG rod with concave-shape end surfaces on SHG efficiency is compensated by the insertion of a λ/8 plate into the cavity. At the repetition frequency of 9 kHz, the 532 nm laser achieves a maximum output power of 23.8 W, a pulse duration of 60 ns (FWHM), and a beam quality factor of Mx 2 × My 2 = 1.52 × 1.43. Compared with the λ/4 plate and without plate, the maximum average power of the laser with the λ/8 plate has increased by 22.7% and 66.4%, respectively, the beam quality factor has also been greatly improved correspondingly. This method provides a new solution for lasers to compensate thermally induced birefringence.

Compact high-power 320-nm continuous-wave single-frequency laser based on power scaling of a diode-pumped Pr:LiYF4 ring laser at red.

Single-frequency (SF) lasers in the visible spectral region are usually obtained through an indirect method, i.e., frequency doubling of near-infrared SF lasers. In this work, we report on the direct generation of a high-power continuous-wave (CW) SF laser in red based on a diode-pumped Pr:LiYF4 (YLF) ring cavity technology. A maximum output power is scaled to 3.98 W at 640 nm with a linewidth of about 17.2 MHz and a power stability of 0.6%. Moreover, by inserting a LBO crystal into the ring cavity for intracavity frequency doubling of the 640 nm SF laser, we have also successfully demonstrated an ultraviolet (UV) SF laser at 320 nm, for the first time to the best of our knowledge, with a maximum power of 670 mW. This work provides a promising route for the development of simple, compact, and high-power SF lasers operating in visible and UV spectral regions.

20 Watt single-frequency 509 nm laser by single-pass second harmonic generation in an LBO crystal

High power 509 nm continuous-wave (CW) lasers have important applications in science and communication. Here we demonstrate a robust high-power single-frequency 509 nm laser system based on nonlinear phase demodulation technique and single-pass second harmonic generation (SHG) configuration. In experiments, the single-frequency fundamental wave at 1018 nm was linewidth-broadened by an electro-optical modulator and then amplified to 207 W in a ytterbium-doped fiber amplifier. In subsequent single-pass SHG stage, over 20 W CW single-frequency 509 nm laser was generated in a LiB3O5 crystal with a SHG efficiency of 9.7%. To the best of our knowledge, this is the highest reported power for CW single-frequency 509 nm laser, which could be used for advanced underwater optical communication and preparation of cesium Rydberg state.

High-power, narrow linewidth solid-state deep ultraviolet laser generation at 193 nm by frequency mixing in LBO crystals

High-power, narrow linewidth solid-state deep ultraviolet laser generation at 193 nm by frequency mixing in LBO crystals

Second harmonic generation of visible vortex laser based on a waveguide-grating emitter in LBO.

In this work, we propose a practical solution to visible vortex laser emission at 532 nm based on second harmonic generation (SHG) in a well-designed waveguide-grating structure. Such an integrated structure is fabricated by femtosecond laser direct writing (FsLDW) in an LBO crystal. Confocal micro-Raman spectroscopy is employed for detailed analysis of FsLDW-induced localized crystalline damage. By optical excitation at 1064 nm, the guiding properties, SHG performance, as well as vortex laser generation of the waveguide-grating hybrid structure are systematically studied. Our results indicate that FsLDW waveguide-grating emitter is a reliable design holding great promise for nonlinear vortex beam generation in integrated optics.

Tunable ultraviolet laser based on intracavity third harmonic generation of external cavity surface emitting laser

Ultraviolet laser has high frequency, short wavelength, large single-photon energy, and high spatial resolution, and has wide applications in many fields such as fine processing, life sciences, and spectroscopy. In this work, a wavelength tunable ultraviolet laser based on intracavity third harmonic generation from an external-cavity surface-emitting laser is reported. The W-type resonant cavity of the laser is composed of a distributed Bragg reflector (DBR) at the bottom of the gain chip, three plane-concave mirrors, and a rear plane mirror. On the arm containing the gain chip, a birefringent filter is inserted at the Brewster angle as the polarization and wavelength tuning element, which can also narrow the linewidth of the fundamental laser to a certain extent. A type-I phase-matched LBO crystal is placed on the beam waist between the folding mirrors M2 and M3 to convert the 980 nm fundamental laser into 490 nm blue light, and a type-I phase-matched BBO crystal is inserted in the beam waist near the rear mirror to produce a 327 nm ultraviolet output from the remained 980 nm fundamental laser and the frequency-doubled 490 nm second harmonic. Before the BBO crystal, a half-wave plate at 980 nm is employed to change the polarization of the fundamental laser, so as to meet the type-I phase-matching condition of the used BBO crystal. Owing to the larger nonlinear coefficient of the type-I phase-matched BBO crystal, and its obviously higher transmittance at 327 nm wavelength than the usually used LBO crystal, the output power is obtained to be 538 mW at 327 nm ultraviolet wavelength, corresponding to a conversion efficiency of 1.1% from pump light to ultraviolet laser. The experiment is performed under conditions of 15 ℃ temperature, 47 W absorbed pump power, 5 mm-length LBO and 5 mm-length BBO crystals. By using a 2 mm-thick birefringent filter as the tuning element, 34.1 nm tuning range of the 980 nm fundamental laser, 14.3 nm tuning range of the 490 nm second harmonic, and 8.6 nm tuning range of the 327 nm third harmonic are obtained. The ultraviolet laser exhibits good beam quality as well as acceptable power stability with the maximum power fluctuation less than 2% within 4.5 h.

Intracavity frequency-doubled external-cavity surface-emitting blue laser with high conversion efficiency

Blue laser with high power and high beam quality has many applications such as in laser display, underwater communication and imaging, and non-ferrous metal processing. Optically pumped external-cavity surface-emitting laser combines the advantages of both surface-emitting semiconductor lasers and solid-state disk lasers, and can produce high output power and good beam quality simultaneously. Its high intracavity circulating power is more conducive to intracavity frequency doubling, achieving high-power and high beam quality blue light through fundamental laser in the near-infrared waveband. This paper reports an efficient intracavity frequency doubled 490 nm high power blue light by using a 980 nm fundamental laser in an external-cavity surface-emitting laser. The V-type resonant cavity is formed by the high reflectivity distributed Bragg reflector (DBR) at the bottom of gain chip, a folded flat concave mirror (high reflectivity coated for 980 nm and anti-reflectivity coated for 490 nm), and a flat concave end mirror (high reflectivity coated for 980 nm and 490 nm). By inserting a nonlinear crystal LBO into the cavity at the beam waist formed by the folded mirror and end mirror, and employing a birefringent filter (BRF) to polarize the fundamental laser and narrow the linewidth of the laser, a high power and high beam quality blue laser with high conversion efficiency is obtained. The effects of different factors including the length of nonlinear crystal, the linewidth of fundamental laser, and the compensation of walk off angle on the output power of the blue laser are studied experimentally. The length of the nonlinear crystal is optimized based on the size of the fundamental laser beam waist at the position of the crystal in the resonant cavity. Under the type-I phase matching condition of LBO, over 6 W output power at 491 nm wavelength is obtained when the crystal length is 5 mm and the BRF thickness is 1 mm. The beam quality <i>M</i><sup>2</sup> factor in the <i>x</i> direction and the <i>y</i> direction are both 1.08, and the conversion efficiency of frequency doubling is 63%. The experimental results also show that symmetrically placed nonlinear crystals can compensate for the walk-off angle during frequency doubling to a certain extent, thereby clearly improving the conversion efficiency of the frequency doubled blue laser.

Yellow-orange wavelength-switchable laser emission generated from c-cut Nd:YVO4 self-Raman with 890 and 259 cm−1 shifts

Wavelength-switchable output at yellow-orange waveband was achieved based on second harmonic generation (SHG) and sum frequency generation (SFG) of c-cut Nd:YVO4 crystal self-Raman laser operation with 890 and 259 cm−1 shifts. Cascade-shifted the fundamental wave (1066 nm) to the first-Stokes wave (1178 nm) with 890 cm−1 shift and then to the second-Stokes wave (1216 nm) with 259 cm−1 shift was realized. Visible laser with 589, 598 and 608 nm wavelength-switchable output was achieved in temperature tuning LBO crystal, which were converted from the 1178 and 1216 nm by second order optical nonlinear processes. Under a diode pump power of 17.7 W, output powers of 2.56, 1.07, and 1.76 W were obtained for visible laser at 589, 598 and 608 nm wavelengths, respectively. These results highlight a promising approach of generating new visible wavelengths based SHG and SFG of Nd:YVO4 self-Raman laser with the 259 cm−1 shift participated, which could fill the visible gap of the wavelengths generated in those of Nd:YVO4 self-Raman laser with only primary shift of 890 cm−1.

High-energy acousto-optic Q-switched alexandrite laser with wavelength tunable fundamental and UV second harmonic generation

We investigate high-energy mJ-class diode-pumped acousto-optic (AO) Q-switched alexandrite lasers with broad tunability at both the fundamental near-IR wavelength range and second harmonic generation (SHG) in the UV wavelength range. An AO Q-switched alexandrite laser with continuous-wave diode-pumping has been operated at up to 10 kHz and producing pulse energy of 700 µJ at repetition rate of 1 kHz. With pulsed double-pass diode-pumping, we demonstrate higher pulse energy of 2.6 mJ. With wavelength tuning, this laser system demonstrated broad fundamental tuning range from 719 to 787 nm with diffraction-limited beam quality (M2 = 1.05). By external cavity second harmonic generation in a Type-I LBO crystal, pulse energy of 0.66 mJ is generated at 375 nm and with UV tuning range from 361 to 391 nm. To our knowledge, this is the first demonstration of AO Q-switched alexandrite laser with broad wavelength tuning in the near-IR and UV wavelength ranges and shows its excellent potential as a pulsed source for future applications.

67 mJ, 137 ns narrow bandwidth 355 nm UV laser.

A high-efficiency, high-energy, narrow bandwidth, hundred-nanosecond pulse width 355 nm ultraviolet (UV) laser was realized. A high-energy single-frequency 1064 nm fundamental laser was demonstrated firstly with multistage end-pumped preamplifiers and side-pumped main amplifiers. The corresponding pulse energy, repetition rate, pulse duration, bandwidth, and beam quality factor M2 were determined to be 221 mJ, 100 Hz, 156 ns, 2.25 MHz, and 1.23, respectively. By using type-I phase-matching LBO crystal for second harmonic generation (SHG) and type-II phase-matching LBO crystal for the sum frequency generation of the third harmonic, 67 mJ, a narrow bandwidth 355 nm UV laser was obtained with a pulse width of 137 ns and an energy stability of RMS < 1.2%@2 h. The fundamental to UV optical conversion efficiency was 30.3%. Our results provided a new way for generating high-energy, narrow bandwidth hundred-nanosecond 355 nm UV lasers used for direct-detection Doppler wind lidar (DWL) system.

Compact continuous-wave solid-state Raman lasers at 707 and 714 nm for laser trapping and cooling of atomic strontium and radium.

Two compact laser sources at 707 and 714 nm are realized efficiently by using a diode-pumped a-cut Nd:YVO4 laser with intracavity stimulated Raman scattering and sum-frequency generation (SFG). The fundamental wave at 1342 nm is generated by the 4F3/2 → 4I13/2 transition in Nd:YVO4 crystal. The Raman Stokes waves at 1496 and 1526 nm were obtained by placing the c-axis of the Nd:YVO4 crystal along the Ng and Nm axes of an Np-cut KGW crystal, respectively. LBO crystals with critical phase matching are used to perform the intracavity SFG of fundamental and Stokes waves. At a pump power of 36 W, the maximum output powers at 707 and 714 nm can reach 2.72 and 3.14 W, corresponding to light-to-light conversion efficiencies of 7.5% and 8.7%, respectively. The developed 707 and 714 nm laser sources are practically useful in laser trapping and cooling related to atomic strontium and radium.

Selectable two-wavelength Nd:YVO4 Raman laser at 671 and 714 nm.

A compact efficient continuous wave (CW) laser with selectable two wavelengths at 671 and 714 nm is developed. The laser cavity comprises an Nd-doped and an undoped YVO4 crystal to generate the fundamental wave at 1342 nm and the first-Stokes Raman wave at 1525 nm, respectively. A single LBO crystal with the cut angle in the XZ plane is designed to achieve the selectable phase-matching via the thermal tuning for the second harmonic generation (SHG) of 1342 nm and the sum frequency generation (SFG) of 1342 and 1525 nm. At a pump power of 40 W, the optimal output powers at 671 and 714 nm can reach 4.5 and 1.8 W, respectively. The present compact CW laser source at 671 and 714 nm has practical usefulness for laser spectroscopy and numerous applications.

High beam quality yellow laser at 588 nm by an intracavity frequency-doubled composite Nd:YVO4 Raman laser.

High beam quality 588 nm radiation was realized based on a frequency-doubled crystalline Raman laser. The bonding crystal of YVO4/Nd:YVO4/YVO4 was used as the laser gain medium, which can accelerate the thermal diffusion. The intracavity Raman conversion and the second harmonic generation were realized by a YVO4 crystal and an LBO crystal, respectively. Under an incident pump power of 49.2 W and a pulse repetition frequency of 50 kHz, the 588 nm power of 2.85 W was obtained with a pulse duration of 3 ns, corresponding to a diode-to-yellow laser conversion efficiency of 5.75% and a slope efficiency of 7.6%. Meanwhile, a single pulse's pulse energy and peak power were 57 µJ and 19 kW, respectively. The severe thermal effects of the self-Raman structure were overcome in the V-shaped cavity, which has excellent mode matching, and combined with the self-cleaning effect of `Raman scattering, the beam quality factor M2 was effectively improved, which was measured optimally to be Mx 2 = 1.207, and My 2 = 1.200, with the incident pump power being 49.2 W.

Secondary Raman and Brillouin mode suppression in two- and three-mirror-cavity diamond Raman lasers.

We report an investigation into secondary mode suppression in single longitudinal mode (SLM) 1240 nm diamond Raman lasers. For a three-mirror V-shape standing-wave cavity incorporating an intra-cavity LBO crystal to suppress secondary modes, we achieved stable SLM output with a maximum output power of 11.7 W and a slope efficiency 34.9%. We quantify the level of χ(2) coupling necessary to suppress secondary modes including those generated by stimulated Brillouin scattering (SBS). It is found that SBS-generated modes often coincide with higher-order spatial modes in the beam profile and can be suppressed using an intracavity aperture. Using numerical calculations, it is shown that the probability for such higher-order spatial modes is higher for an apertureless V-cavity than in two-mirror cavities due its contrasting longitudinal mode-structure.

High power and conversion efficiency intracavity ultraviolet laser at 355 nm

In this study, we investigated and provided a compact and efficient diode-pumped-solid-state ultraviolet laser at 355 nm with high commercial value. The 355 nm laser was coupled out with an uncoated Brewster-cut LBO crystal in order to prolong its lifetime. A maximum output power of 12.2 W was generated when pump power was 74.5 W and the pulse repetition rate was 40 kHz. The conversion efficiency from pump laser to ultraviolet laser was 16.4 %, which we believe to be the highest among the reported papers in which the pump source was 887 nm. The stability of 355 nm laser power was less than ± 1 % at 12 W over 20 h. Output characteristic of ultraviolet beam varying with the temperature of two LBO crystals was also investigated to located the exact optimal operating temperature.

Generation of 1216 nm and 608 nm laser emission using cascaded Raman shifts in Nd:YVO4

We report the design and operation of two self-Raman lasers optimized for emission at 1216 nm and 608 nm, utilizing a combination of Raman shifts at 890 and 259 cm−1 in c-cut Nd:YVO4 crystal. Key to the efficient operation of these lasers was the use of a double-end diffusion-bonded Nd:YVO4 composite crystal. This enabled the generation of a maximum average output power of 2.6 W at 1216 nm (with a diode-Stokes conversion efficiency of 14.7%) from the Stokes-optimized cavity. With the incorporation of a non-critically phase matched LBO crystal and a slight cavity re-design, the Stokes field at 1216 nm was frequency doubled to the orange part of the visible spectrum (608 nm), where a maximum average output power of 1.71 W was achieved with a diode-orange conversion efficiency of 9.7%.