Intracavity Frequency Doubling Research Articles

Concept for power scaling by harmonic beam coaxial combination in an intra-cavity frequency doubling laser.

A new method of harmonic beam coaxial combination (HBCC) from two intra-cavity frequency doubling branches was demonstrated. Firstly, two identical nanosecond (ns) 532 nm green lasers with high power and good beam quality were created. Each green laser was constructed of an intra-cavity frequency doubling branch based on a laser diode (LD) end-pumped acousto-optical (AO) Q-switched 1064 nm Nd:YVO4 laser in a LiB3O5 (LBO) nonlinear crystal. Each branch generated about 45 W green output at a 50 kHz pulse repetition rate (PRR) with diffraction limited beam quality. The first green beam was injected into the LBO crystal in the second branch, and the pulses from the two branches did not exist simultaneously. Then, the HBCC was performed. Consequently, an 83 W combined green output power at 532 nm was obtained with a combination efficiency of 92.2%. The PRR of the HBCC pulse was doubled to be 100 kHz, with a pulse width of about 22 ns, corresponding to a single pulse energy of 0.83 mJ and a peak power of 37.73 kW. The combined beam quality factor was measured to be M x2 = 1.80 in the x direction and M y2 = 1.71 in the y direction, respectively. Moreover, many more beams could also be combined with this method for further scaling the green power.

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.

1.01-W narrow-linewidth ultra-violet laser by Pr: YLF

We presented the first report of a high-power narrow-linewidth 261 nm laser. This laser relies on a diode-pumped Pr: YLF crystal and employs a ring cavity design that integrates TSAG (Terbium Scandium Aluminum Garnet) as the magneto-optical crystal. A double-ended pumping configuration is established through the utilization of two 10-W 444-nm blue diode laser arrays as pump sources. Through intracavity frequency doubling facilitated by a BBO (Beta-Barium Borate) crystal, we have achieved a final output of 1.01 W narrow-linewidth laser radiation at 261 nm.

Ultra-narrow linewidth in continuous-wave external cavity diamond Raman laser

A continuous-wave narrow linewidth diamond Raman laser based on an intracavity frequency doubling structure was demonstrated. Linewidth narrowing and power enhancement were realized by tuning the phase matching in the second-harmonic generation element through temperature control. A maximum output power of 5 W at 592 nm with a linewidth of 72 MHz was obtained using a Yb doped fiber laser with a power of 40 W and a linewidth of >4 GHz, an enhancement of the linewidth by a factor of about 65. The results indicate that high-power and narrow linewidth lasers can be produced utilizing diamond Raman conversion combined with the phase matching in the second-harmonic generation element.

High beam quality continuous-wave 320 nm UV laser from a walk-off compensated intracavity frequency-doubled Pr:YLF laser

We report a high beam quality continuous-wave (CW) 320 nm ultra-violet (UV) laser. An end-pumped praseodymium-doped yttrium lithium fluoride (Pr:YLF) laser is constructed in a typical V-shaped cavity structure, while the UV output is obtained through intracavity frequency doubling using LiB3O5 (LBO). We investigate the dependence of the UV output power, as well as the spot profile on the LBO length, and find that the “walk-off” within LBO severely affects both the frequency-doubling efficiency and the beam quality of the UV output. Rotated twin LBO crystals are then applied to substitute for single long LBO crystal to compensate the walk-off effect, resulting in high-power 320 nm output up to 410 mW under the absorbed pump power of 4.0 W at 444 nm, with a high beam quality of M x 2=1.02 and M y 2=1.04.

A compact continuous-wave intracavity frequency doubling Pr:YLF ultraviolet laser at 360 nm

We demonstrate a continuous-wave (CW) ultraviolet (UV) laser operating at 360 nm, achieved through intracavity frequency doubling of a Pr:YLF laser. This UV laser is more compact and simpler compared to previously reported designs, due to the adoption of a straight cavity. The total length of the laser system measures 75 mm, with a resonant cavity length of only 25 mm. By utilizing an InGaN laser diode (LD) emitting at 444 nm with a maximum incident power of 3.1 W, we were able to achieve a CW UV laser with an output power of 252 mW. The optical to optical conversion efficiency reached up to 8.1%, and the output power stability remained within ±1.9% over a period of two hours. This innovative UV laser has potential applications in various fields such as spectral analysis, material analysis, bioengineering, optoelectronic detection, and medical treatment.

A high stability and low noise passively Q-switched yellow-green laser with a Ti3C2Tx-PVA saturable absorber

An 808 nm laser diode (LD) end-pumped passively Q-switched Nd: YAG ceramic yellow green laser at 561 nm with high stability and low noise has been demonstrated, for the first time to our knowledge based on passively Q-switching with a Ti3C2Tx-polyvinyl alcohol (Ti3C2Tx-PVA) film, frequency selection and filtering with a Brewster polarizer (BP) and a birefringent crystal (BC), and intracavity frequency doubling with a LiB3O5 (LBO) crystal. The 1112 nm and 1116 nm wavelengths from the Nd: YAG ceramic and the number of longitudinal modes of 1123 nm fundamental frequency light were effectively suppressed by adopting BP and BC. At 5.1 W of the 808 nm LD pump power, the 561 nm-PQYG laser with a maximum average power of 75.5 mW, a maximum repetition rate of 610 kHz, and a narrowest pulse width of 41 ns were obtained, corresponding to an average power instability of ±0.29%, a repetition rate instability ±7.08%, a pulse width instability of ±4.67%, and a laser noise of 0.49% over a period of 4 h.

An LED-Side-Pumped Intracavity Frequency-Doubled Nd,Ce:YAG Laser Producing a 2W Q-Switched Red Beam

We report a high-average-power acousto-optic (AO) Q-switched intracavity frequency-doubled red laser based on a high-efficiency light-emitting-diode (LED) pumped two-rod Nd,Ce:YAG laser module. Under quasi-continuous wave operation conditions, a maximum output power of 1319.08 nm wavelength was achieved at 11.26 W at a repetition rate of 100 Hz, corresponding to a maximum optical efficiency of 13.9% and a slope efficiency of 17.9%. In the active Q-switched regime, the pulse energy of the laser was as high as 800 μJ at a repetition rate of 10 kHz with a pulse width of 1.5 μs. Under non-critical phase-matched KTP crystal conditions, an average power of 2.03 W of 658.66 nm through intracavity frequency-doubling was obtained at a repetition frequency of 10 kHz with a duration of 1.3 μs, and the M 2 factor was measured to be about 5.8. To the best of our knowledge, this is the highest average power of an LED-pumped AO Q-switched 1319 nm laser and intracavity frequency-doubled red laser reported to date.

Intracavity frequency doubling acousto-optic Q-switched high repetition rate high-energy Nd:YLF laser.

The ongoing advancement of Ti:sapphire femtosecond laser technology has drawn increasing attention to high repetition rate, high-energy green lasers as ideal pump sources for Ti:sapphire regenerative amplifiers. This study employed a neodymium-doped yttrium lithium fluoride (Nd:YLF) as the gain medium, supplemented with side-pumped laser diodes, acousto-optic Q-switching, and intracavity frequency doubling technologies. The results demonstrated a repetition rate ranging from 1-10kHz, a pulse width of less than 100ns, and a single pulse energy exceeding 50mJ at 527nm green light output. Furthermore, an operating stability (RMS) of ≤0.15% was maintained for 14h at a repetition rate of 1kHz and an output power of 40W.

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.

High-efficiency 261-nm continuous-wave laser by single-blue-laser-diode-pumped Pr3+:LiYF4 crystal

High-power continuous-wave (CW) deep ultraviolet lasers attract growing research interest in the field of optoelectronics. Herein, we perform a CW deep ultraviolet laser at 261 nm by the intracavity frequency doubling of a single-blue-laser-diode-pumped Pr3+:LiYF4 (Pr:YLF) laser. The excellent mode matching between the pump and fundamental-frequency laser beams is realized by optimizing the pump focusing and laser resonator systems. On that basis, the maximum CW fundamental-frequency laser obtained is 1.41 W at 522 nm, corresponding to a slope efficiency of 59.12%. Moreover, a deep ultraviolet laser is further demonstrated at 261 nm using a β-BaB2O4 (BBO) frequency-doubling crystal, yielding a maximum output power of 1.17 W and an optical–optical conversion efficiency of 33.4% with respect to the pump power. Such a result is the highest optical–optical conversion efficiency of the CW DUV lasers from Pr3+-doped crystals, to the best of our knowledge. The finding in this work manifests the development potential of all-solid-state deep ultraviolet lasers and provides a feasible avenue for achieving high-efficiency deep ultraviolet laser output.

Simple and compact high-power continuous-wave deep ultraviolet source at 261 nm based on diode-pumped intra-cavity frequency doubled Pr:LiYF4 green laser.

We report the recent progress on diode-pumped high-power continuous-wave Pr:LiYF4 (YLF) green laser and deep ultraviolet (DUV) laser generation via intracavity frequency doubling. Using two InGaN blue diode lasers as pump source to form a double-end pumping geometry, in this work, we have demonstrated a green laser at 522 nm with a maximum output power of 3.42 W, which is believed to be the highest power ever achieved in all-solid-state Pr3+ lasers in this specific spectral region. Moreover, by intracavity frequency doubling of the achieved green laser, we have further obtained a DUV laser at about 261 nm with a maximum output power of 1.42 W, which is far higher than previous results. The watt-level 261-nm laser paves the way towards the realization of simple and compact DUV source for a variety of applications.

Microsecond pulsed yellow emission by intracavity doubled optically pumped two-chip VECSEL

A quasi-continues-wave (QCW) 100 μs pulsed yellow laser at 589 nm, based on intracavity frequency doubling (ICFD) of identical two-chip vertical-external-cavity surface-emitting laser (VECSEL) with bow-tie configuration, is demonstrated. Each VECSEL chip is optically QCW-pumped by an 808 nm laser diode, emitting a fundamental wavelength around 1178 nm. A birefringence filter is inserted in the laser cavity to select the linear p-polarized oscillation and tune the operation wavelength. Using a lithium-triborate (LiB3O5) as the frequency doubled crystal, a total frequency doubled output power of 264 mW at 589 nm is achieved, operating at a pulse duration of 194 μs and a pulse repetition rate of 1 kHz. A good beam quality factor is measured to be M 2 = 2.15. These results represent a novel scheme for the QCW multiple gain chips VECSEL ICFD system, opening up a new perspective for the realization of impact long pulse 589 nm laser for sodium guide-star.

Diode-pumped high-power continuous-wave intracavity frequency-doubled Pr3+:YLF ultraviolet lasers around 349 nm

Abstract High-power continuous-wave ultraviolet lasers are useful for many applications. As ultraviolet laser sources, the wavelength switching capability and compact structure are very important to extend the applicability and improve the flexibility in practical applications. In this work, we present two simple and relatively compact schemes by laser diode pumping to obtain a watt-level single-wavelength 348.7-nm laser and discrete wavelength tunable ultraviolet lasers around 349 nm (from 334.7 to 364.5 nm) by intracavity frequency doubling based on Pr3+:YLF and $\unicode{x3b2}$ -BBO crystals. The maximum output power of the single-wavelength 348.7-nm laser is 1.033 W. The output powers of the discrete wavelength tunable lasers are at the level of tens of milliwatts, except for two peaks at 348.7 and 360.3 nm with output powers of approximately 500 mW. In addition, simulations are carried out to explain the experimental results and clarify the tuning mechanisms.

Power and energy scaling of an acousto-optically Q switched Raman deep-red laser.

An efficient high-power nanosecond pulsed deep-red laser at 745 nm is produced by intracavity frequency-doubling an acousto-optically Q switched Nd:YLF/KGW Raman laser using a lithium triborate (LBO) crystal. The critically phase-matched type-I LBO crystal with an optimized length of 25 mm is adopted to enable efficient second-harmonic generation and to suppress unwanted cascaded Stokes fields. Under a repetition rate of 4 kHz, the maximum average output power of 4.1 W is obtained with the launched pump power of 50 W, resulting in an overall optical power conversion efficiency of 8.2%. The average beam quality factor is determined to be M2 = 1.46. The pulse energy is scaled up to 3.3 mJ at the repetition rate of 1 kHz, corresponding to a pulse width of 4.2 ns and a peak power of up to 0.8 MW. Moreover, we theoretically investigate the dependence of the conversion efficiency on the walk-off angle as well as the fundamental and first-Stokes losses, which will guide further optimization of experimental devices.

Simulation and experimental investigation of a 6.6 ps passively mode-locked TEM00 Nd:YVO4/KTP green laser based on SESAM

The design, construction, and characterization of a diode-pumped SESAM mode-locked green laser were reported. Based on the simulation results, the technical route for the construction and optimization of the resonator was determined. A KTP was used as the intracavity frequency doubling crystal. The maximum output average power at 532 nm was 500 mW with a repetition rate of 82 MHz at a pump power of 5 W. In addition, the measured and simulated beam quality was about , indicating the single-mode operation of the laser. Moreover, the spectral characteristics of the laser at 1064 nm and 532 nm were analyzed. The time duration of the pulses at 1064 nm was about 9.4 ps. The theoretical calculations based on the time-bandwidth product evaluation method predicted the time duration of 6.6 ps for the pulses at 532 nm.

Tunable, Continuous-Wave, Deep-Ultraviolet Laser Generation by Intracavity Frequency Doubling of Visible Fiber Lasers

Deep ultraviolet (DUV) lasers are essential elements to versatile applications such as spectroscopy and lithography, and several techniques including free-electron lasers, excimer lasers and high-order harmonic conversion have been developed for DUV laser generation, yet the wavelength tunability and compactness are still challenging. Here, for the first time, we experimentally demonstrate a compact tunable continuous-wave (CW) DUV laser source by direct intracavity frequency doubling of visible fiber lasers. Efficient green/yellow laser emission is enabled by the down-conversion in the Ho <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3+}$</tex-math></inline-formula> - or Dy <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3+}$</tex-math></inline-formula> -doped ZBLAN fibers while the miniaturized cavity consists of a home-made fiber pigtail mirror and diffraction grating. The second harmonic generation from visible to ultraviolet is subsequently implemented by utilizing a BBO module intracavity. The achieved CW DUV lasers yield wavelength tuning range of 269.5-275.4 nm and 283.6-289.9 nm in the presence of an ultra-narrow linewidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 0.025 nm. The produced power at 272.6 nm reaches 1.36 mW and a maximum visible-to-DUV efficiency of 5.3‰ is estimated with the green laser excitation. Our work therefore provides new possibilities for the realization of a new class of compact, wavelength tunable, and cost-effective CW DUV laser sources.

The single‐wavelength 561 nm laser based on reflective volume Bragg grating

AbstractThis article presents 561 nm single‐wavelength laser by laser diode end‐pumped Nd:YAG crystal. The reflective volume Bragg grating is used as the output coupling mirror to effectively select the center wavelength of 1123 nm. The single wavelength laser output at 561 nm is obtained by intracavity frequency doubling via LBO crystal cut in accordance with Type I phase matching condition. When the pump power is 4 W, the output power reaches 229.6 mW, and the power instability is less than 3% within 5 min. Experiments show that the reflective volume Bragg grating acts as both a frequency selection element and an output coupling mirror, which simplifies the resonator structure and improves the laser output power.

Towards Power Scaling of Simple CW Ultraviolet via Pr: LiYF4-LBO Laser at 320 nm

Intracavity frequency doubling of diode-pumped continuous-wave Pr^3&#x002B; laser in visible spectral region is a highly efficent and cost-effective method for the generation of high-performance continuous-wave ultraviolet laser. However, to date, diode-pumped continuous-wave frequency doubled Pr^3&#x002B;-based ultraviolet laser has still been power limited only to about one watt. In this work, employing two 12-W blue diode lasers as pump sources individually, we achieved maximum output powers up to 1.82 W and 1.73 W of ultraviolet lasers at about 320 nm by intracavity frequency doubling of continuous-wave Pr:LiYF₄ (YLF) lasers at 640 nm. The used nonlinear frequency doubler is a 12-mm LBO crystal. For further power scaling of the ultraviolet laser, a total pump power of 24 W was injected into the laser crystal by configuring a double end pumping geometry. Under this situation, a maximum output power of 3.22 W can be achieved, which is believed to be the highest continuous-wave ultraviolet laser via intracavity frequency doubling. This solid-state 320-nm ultraviolet laser could replace the relatively cumbersome He-Cd vapor laser for a variety of applications.

Theoretical and experimental researches on the walk-off compensation of an intracavity doubling red laser using a twin-BIBO-crystal

We theoretically and experimentally researched on an intracavity frequency doubling red laser with walk-off compensation of bismuth borate (BIBO) for the first time, to the best of our knowledge. Through theoretical investigations, we described in detail the spatial walk-off characteristics of a BIBO crystal and discussed quantitatively the influence of different arrangements of a twin-BIBO-crystal on the output power of a second harmonic wave. Furthermore, the progress of walk-off compensation was revealed with the arrangement having the second BIBO 180° rotated along extraordinary axis. Experimentally, we found that the maximum average output power with walk-off compensation has been improved by 1.2 times compared to the uncompensated case, and the corresponding intensity profile restored from an oblique ellipse to an approximate circle.