Solid-state Laser Research Articles

Compact Diode-Pumped Solid-State Laser with Intracavity Pump-Enhanced DFG Emitting at ~3.5 Microns

We report a diode-pumped solid-state (DPSS) laser used for intracavity pump-enhanced difference frequency generation (DFG) to create a 3.5-micron laser. Using a 50 mm-long periodically poled lithium niobate (PPLN) crystal inside the cavity of an Nd:YVO4 solid-state laser at 1064 nm with 4.5 W pump power at 808 nm, and a 310 mW C-band signal at 1529 nm, up to 31 mW of mid-infrared output power at 3499 nm is obtained. The cavity requires no active stabilization and/or locking, and the entire cavity is <8 cm in length. The obtained output power corresponds to a black-box efficiency of 2.20%W−1, which is the highest value reported to date for continuous-wave DFG based on a bulk nonlinear optical crystal with no active stabilization. Potential future applications in free-space optical communication are also discussed.

Beam quality control technology for solid-state lasers based on thermal effects.

Thermal effects under high-power pumping significantly limit the laser beam quality. To address this, we developed an M2 simulation algorithm based on ray trajectory simulation and established a corresponding experimental platform. This approach optimized the M2 factor of pulsed lasers to 2.2 and output power of 25.9 W under a repetition rate of 10 kHz. The results revealed that under specific conditions, thermal effects, typically considered detrimental to beam quality, could significantly enhance it. Compared to other methods necessitating additional optical components, our strategy offers a streamlined and straightforward solution for beam quality control under high-power pumping conditions.

Infrared Saturable Absorption Properties of Tungstenene Nanosheets for Passively Q-Switched 1.9 μm Solid-State Laser

Infrared Saturable Absorption Properties of Tungstenene Nanosheets for Passively Q-Switched 1.9 μm Solid-State Laser

Growth and spectral properties of a novel praseodymium-doped alpha-barium borate laser crystal

A novel Praseodymium-doped borate (Pr:α-BBO) laser crystal was grown successfully by using the Czochralski method. The phase structure, absorption and fluorescence lifetime, as well as blue laser diode (LD) pump performances of Pr:α-BBO were totally studied. The segregation coefficient and valence state of Pr ions in the crystals were investigated using inductively coupled plasma atomic emission spectroscopy and X-ray photoelectron spectroscopy. A 450 nm blue LD was employed to carry out a pump experiment on the Pr:α-BBO slab crystal with a doping concentration of 0.22 at.%. The main emission peaks of Pr3+ ions in the orange-red light band were found to be at 611.5 nm, 634.7 nm, and 638.3 nm. The experimental results show that the Pr:α-BBO crystal exhibits higher orange light fluorescence emission performance, with an emission peak intensity at 611 nm that is 2.1 times stronger than that at 635 nm due to the splitting of the 3P0→3F2 transition (635 nm). By optimizing the Pr:α-BBO laser crystal growth process and further solid-state laser experiments, it can be expected to have broad applications in laser medicine, spectral detection, and nonlinear optical frequency conversion fields.

Effect of introducing KNO3 on the preparation of athermal fluorophosphate glass and investigation on its thermo-optical property

The effects of introducing some amount of KNO3 into the raw materials on preparation of fluorophosphate glass are investigated in terms of UV–vis transmittance, absorption coefficient and change of refractive index. As the content of KNO3 reaches 50%, the UV absorption coefficient of the optimized fluorophosphate glass reaches the minimum due to absence of microcrystals in the produced glass. The Schott's Sellmeier dispersion formula and Ghosh's two-polar wavelength-dependent Sellmeier equation were both used to calculate dispersion constants of the optimized fluorophosphate glass. The optimized fluorophosphate glass maintains special characteristics of negative temperature coefficient of refractive index and near-zero thermo-optical coefficient. The lower absorption both in UV and near-infrared (NIR) helps to improve its laser-induced damage resistance. The athermal fluorophosphate glass shows great potential for compensation of thermal-induced distortion in high-power solid-state lasers and high-resolution optical systems.

Electro-optic solution to overcome the transient regime of a cavity dumped UV laser source?

Laser marking is one of the main industrial applications of lasers. To mark many materials or to obtain patterns of small dimensions, triggered pulsed solid laser sources are increasingly used emitting in the fundamental in the infrared and to which two nonlinear (NL) stages are added to obtain an emission in the UV. The conversion efficiency as well as that of the marking then depends mainly on the peak power of the UV pulses generated. One of the solutions for obtaining a higher peak power is to reduce the duration of the laser pulses. To do this, it is possible to change the architecture of the laser cavity by switching from a Q-Switch operating mode (QS) to a cavity dumped mode (CD). With this architecture it is thus possible to reduce the duration of the pulses by an order of magnitude. This peak power gain is unfortunately achieved at the cost of a very long transient regime, up to a few tens of milliseconds, compared to the classic QS which generally only occurs for the first laser pulse. Unfortunately, laser marking is by nature based on chopped operation for the laser, which corresponds to working permanently in a transient state. Marking with a CD architecture laser is then often full of defects and therefore unacceptable in terms of quality. After a study of the problem specific to the use of a UV source with CD architecture in the context of marking, we propose an original solution to dissociate the chopped regime, specific to marking, from the transient regime of the laser. This solution is based on the use of an RTP (Rubidium Titanyle Phosphate RTiOPO4) electro-optical crystal placed between the laser output and the NL stages. This crystal is driven like a half-wave plate by high voltage square pulses of a duration corresponding to the duration of the marking laser pulse trains. This thus makes it possible to obtain laser operation in a stabilized regime, therefore outside the transient regime, and simultaneously chopped operation characteristic of laser marking. The new operating mode obtained is characterized in detail with the new marking performances which prove to be optimal and compatible with the requirements of a quality marking. In addition to making the CD architecture compatible with laser marking, this solution also makes it possible to adjust the average power, and therefore the energy of the laser pulses to adapt it according to the materials and this without changing the thermal behavior of the laser. Last advantage, by adjusting the extinction voltage applied to the RTP outside the cavity, it is also possible to keep a few milliwatts of the marking laser beam as the aiming beam, with the certainty of perfect alignment with the full power beam.

A low-cost, highly efficient solid-state dye laser made of Rhodamine B dopped photopolymer host cured by mercury or halogen lamp

In this work, we designed a rod shape solid-state laser gain media (GM) that can produce amplified spontaneous emission (ASE) in the 630–670 nm region. The GM is made with Rhodamine B (RhB) dissolved in acetone mixed with commercially available rapid photopolymer (PP) resin that predominately (80 %) contains 3-nitro-9-octyl-9H-carbazole (NOCB) and solidified with mercury or halogen lamp. We used a solid-state matrix laser (SSL) rod of RhB embedded NOCB. The results showed that the photoluminescence (PL) of SSL was at approximately 630 m, and the absorption peak was at 575 nm. The concentration of the RhB in acetone was varied from 25 mg/ml to 100 mg/ml and mixed in a 1:10 ratio volume/weight (v/w). GM could be pumped transversely using 355 nm (3rd Harmonic of Nd: YAG) or 405 nm diode laser or a UV lamp. The GM was initially designed with the aim to be pumped using 532 nm since the resin solidified using UV and blue light irradiation. Supersizing, we found that after complete polymerization, optical pumping using 355 nm can be employed to produce ASE. The main advantage of using these SSL are (i) ease of manufacturing, (ii) simplicity to scale up, (iii) low cost, and (iv) 3D printer compatibility. It also has potential applications in the military, science, and medicine, especially facial rejuvenation.

Watt-Level Diode-End-Pumped Self-Mode-Locked Tm,Ho:LLF Laser

A diode-end-pumped self-mode-locked Tm,Ho:LuLiF4 (LLF) laser is demonstrated for the first time, to the best of our knowledge. At the incident pump power of 3.4 W, the stable self-mode-locked operation of the Tm,Ho:LLF laser was realized without any additional devices in the resonator. Further increasing the incident pump power to 6.8 W, the maximum average output power of 1.07 W was achieved at 2068 nm with a pulse width of 746 ps and a repetition frequency of 468 MHz. The experimental results indicate that the Tm,Ho:LLF crystal is promising to generate the high-power self-mode-locked solid-state laser at 2 μm waveband. The self-mode-locked Tm,Ho:LLF laser has potential applications in optical communication, remote sensing, material process, and nonlinear frequency conversion.

Broadband near infrared photoluminescence of Cu2+‐doped corundum (α‐Al2O3)

AbstractCopper‐doped corundum (α‐Al2O3) possesses an intense broadband photoluminescence in the near infrared. This photoluminescence is originated from Cu2+ ions, which substitute for Al3+ ions in corundum lattice. Co‐doping with Ge is necessary to obtain the luminescent material. It seems, that simultaneous introduction of Ge is needed to provide the charge compensation for heterovalent Cu2+ → Al3+ substitution, in such a way that the whole process (Cu2+, Ge4+) → 2Al3+ is charge‐balanced. The broad photoluminescence spectrum matches well with transparency window of silica optical fibers and the quantum yield seems to be satisfactory, so copper‐doped corundum can become demanded as a new active media for solid state lasers and amplifiers. This is the first example of photoluminescence from octahedrally coordinated Cu2+ ion in oxide materials.

Development of the 2.7 μm to 3 μm Erbium-Doped Laser

The 3 μm wavelength band laser is located on the strong absorption peak of water and the atmospheric transmission window. The 3 μm laser with high single pulse energy is used in medical treatment for cutting soft tissues and bones during surgery. It is used as a pump source for optical parametric oscillators, and Fe lasers can realize 3~5 μm or 8~14 μm laser output, which has an irreplaceable role in certain areas (e.g., optoelectronic countermeasures, LIDAR, atmospheric monitoring, etc.). Commercial semiconductor-pumped Er lasers are capable of achieving 3 μm laser output of 600 mJ with the maturation of a 970 nm semiconductor laser. The conversion efficiency is significantly improved. However, the energy is lower than a flash-lamp-pumped Er laser. There are still serious crystal thermal effects and an inefficient conversion process. In this paper, the energy-level systems of 3 μm Er-doped lasers are discussed. A summary of the current state of research on Er lasers using different matrices and the commercialization of Er-doped lasers with wavelengths ranging from 2.7 μm to 3 μm is also provided. Several technical means are given to enhance laser performance. Furthermore, the development of Er-doped solid-state lasers with wavelengths between 2.7 and 3 μm is envisaged in the near future.

Cavity Lasing Characteristics of Thioflavin T and Thioflavin X in Different Solvents and Their Interaction with DNA for the Controlled Reduction of a Light Amplification Threshold in Solid-State Biofilms.

The lasing characteristics of Thioflavin T (ThT) and Thioflavin X (ThX) dyes were investigated in solvents with increasing viscosity: water, ethanol, butanol, ethylene glycol, and glycerol and three forms of DNA (double-helix natural, fragmented, and aggregated). The results identified that lasing thresholds and photostability depend on three critical factors: the solvation shell surrounding dye molecules, the organization of their dipole moments, which is driven by the DNA structure, and the molecules diffusion coefficient in the excitation focal spot. The research highlights that dye doped to DNA accumulated in binding sites fosters long-range dye orientation, facilitating a marked reduction of lasing thresholds in the liquid phase as well as amplified spontaneous emission (ASE) thresholds in the solid state. Leveraging insights from lasing characteristics obtained in liquid, ASE in the solid state was optimized in a controlled way by changing the parameters influencing the DNA structure, i.e., magnesium salt addition, heating, and sonication. The modifications led to a large decrease in the ASE thresholds in the dye-doped DNA films. It was shown that the examination of lasing in cavities can be useful for preparing optical materials with improved architectures and functionalities for solid-state lasers.

High-power and efficient vortex Nd:YVO4 laser using annular pumping

Optical vortex lasers that carry orbital angular momentum are of great significance for many applications. A high-power and efficient continuous-wave vortex Nd:YVO4 laser at 1064 nm was demonstrated with annular pumping based on an axicon. The high-quality LG01 vortex beams with maximum output power up to 6.25 W was achieved under the absorbed pump power of 14.4 W, corresponding to an optical conversion efficiency of 43.4% and a slope efficiency of 44.8%, respectively. Controlling the wavefront handedness of the LG01 beam was simply achieved by carefully adjusting the output coupler and the window inserted in the resonator. This study shows that annular pumping based on an axicon would have great potential in the development of high-power vortex solid-state lasers with simple and compact resonator structure.

The First Clinical and Functional Results of Myopia Correction Using a Solid-State Laser Unit

Relevance. Modern keratorefractive surgery (CRS) is a high-tech field of ophthalmology aimed at solving various problems of correcting a wide range of ametropias. Increasing the security of the RFI is one of the priority areas Purpose. To analyze the clinical and functional results of the use of the “Olimp™-2000” solid-state laser system during CRS using the method of superficial and sublamellar laser keratoablation and formulate recommendations for the therapeutic management of patients. Materials and methods. 53 patients (106 eyes) were examined, the average age was 28.5 ± 2.4 years. The inclusion criterion was moderate myopia and the absence of contraindications to CRC. If sufficient, taking into account safety criteria, CRS was performed by sublamellar keratoablation, if insufficient, superficial keratoablation was performed. In both cases, ablation was performed using a domestic solid-state laser machine. The observation period was 3 months. Pharmacological support in all cases was standard, adopted for the management of patients in FCMMG “YourMed”. Results. An analysis of the clinical and functional results of CRS using a solid-state laser device showed full compliance with the criteria set by the Food and Drug Administration (FDA). The accuracy of hitting the target refraction in the range of ± 0.5 diopters was 99.2 %; in 3 months of observation, no regression of the obtained refractive result was observed in any case. There was no loss of lines in any case, the BCVA after the operation corresponded to or exceeded by 1–2 lines the BCVA before the operation. When performing superficial keratoablation, in two cases, the loss of line 1 of the NCVA was noted due to the development of early subepithelial fibroplasia, which required correction of the pharmacological support. Conclusion. The analysis of the clinical and functional results of the correction of moderate myopia using the “Olimp™-2000” solid-state laser device showed high efficiency in terms of efficiency, safety, and predictability, despite little experience in using solid-state ablation in clinical practice. The use of Floas Mono® did not cause side effects in all cases and contributed to the smooth course of the early postoperative period. Thus, this drug is effective in the postoperative period and can be recommended for use in patients after CRC. The generation of ultraviolet radiation by modern solid-state devices for the purpose of correcting ametropia is a promising direction in CRS.

Transform-Limited Sub-100-fs Cr:ZnS Laser with a Graphene-ZnSe Saturable Absorber

In this work, we present ultrashort pulse generation from passively mode-locked Cr:ZnS laser with a monolayer graphene-coated ZnSe substrate exhibiting high nonlinearity. The femtosecond Cr:ZnS laser produces output power up to 330 mW at a 233 MHz repetition rate. Even in the presence of an uneven negative dispersion profile, the enhanced self-phase modulation by the ZnSe substrate of the graphene saturable absorber enables the polycrystalline Cr:ZnS laser to produce slightly chirped 99 fs pulses at 2373 nm. With extracavity dispersion compensation using a mixture of 3 mm and 2 mm thick ZnSe plates, the pulse width was compressed from 99 fs to 73 fs, resulting in an improved time–bandwidth product from 0.431 to 0.318. Assuming a sech2 pulse shape (0.315), the pulses were almost transform-limited. These results indicate that utilizing a graphene saturable absorber on a substrate with high nonlinearity presents an effective method for developing sub-100 fs solid-state lasers within the mid-IR spectral range.

Revisiting the luminescence properties of Er3+, Tm3+ and Ho3+ doped Bi4Ge3O12 rod-type crystal fibers for the laser application

BGO single crystals doped with Er3+, Tm3+ and Ho3+ rare-earth ions were prepared in the form of rod-type crystal fibers via the micro-pulling down technique to perform an extensive investigation of their visible, near- and mid-infrared luminescence properties and to really decide on their interest as solid-state laser media in the various spectral domains. Revisiting and completing the absorption spectra already available in the literature led to the derivation of more reliable “effective” radiative lifetimes and branching ratios. Registration of the fluorescence decays of the most important emitting levels versus dopant concentrations led for the first time to an unambiguous determination of “intrinsic” emission lifetimes – corresponding to negligible contributions from inter-ionic energy-transfers - and non-radiative multiphonon relaxation rates. Such data also allowed for the determination of the dominant phonon energy which comes into play in the electron-phonon coupling responsible for these multiphonon relaxation processes and for its lattice vibration origin, i.e. a high phonon energy of the order of 820 cm−1 corresponding to the coupling between bending vibrations of (GeO4)4- tetrahedra and vibrations corresponding to motions of these (GeO4)4- tetrahedra against the Bi3+ ions for which the rare-earth dopant ions substitute. Using the above data and different methods for the calibration of the registered emission spectra in cross section unit and for the derivation of gain cross section curves finally show that mid-infrared emissions of Er:BGO, Tm:BGO and Ho:BGO around 1.55 μm, 1.9 μm and 2 μm, respectively, occur with comparable gain cross sections as in the most important reference mid-infrared laser materials, although over slightly shifted thus complementary spectral domains. It is shown that potentialities also exist with Tm:BGO in the blue, deep-red and near-infrared spectral domains around 470 nm, 800 nm and 1.45 μm, by pumping the crystals with conventional pump sources and using some suitable co-dopants to avoid detrimental self-terminating processes.

Passive Phase Locking Coherent Combination of Solid-State Lasers through Stimulated Brillouin Scattering Effect

The stimulated Brillouin scattering (SBS) effect, a new approach to the combination of solid-state lasers, can be actualized via coherent synthesis. In this paper, a solid-state laser based on SBS passive phase locking, utilizing the master oscillator power amplifier (MOPA) structure at the front end of the lasers, provides the amplification of the Stokes light subsequently generated. In order to reduce the influence of thermal effects on beam quality, beam-split amplification has been adopted with the same phase locking used by the back injection of the Stokes pulse. With the advantage of the combined scheme, the energy extraction efficiency of SBS coherent combination can be reached at 91.8% with coherent fringe visibility of 83%. Therefore, it provides a new way to improve the brightness through realizing the coherent combination of multi-channel solid-state lasers.

Vaginal treatment with solid state non ablative laser 1470 nm for vaginal atrophy in post menopausal women

One of the most common menopausal symptoms is vaginal dryness. Menopausal sex hormone deficiency causes changes in the urogenital tract, where estrogens are the primary regulators of vaginal physiological functions. Many treatments have been developed over the years, but the majority of them are ineffective or have potential side effects. Actually, laser therapy has the highest efficacy with the fewest (or none) side effects. Thermal energy acting on the vaginal wall has been shown in studies to stimulate collagen synthesis, induce neovascularization, enrich the glycogen epithelium, improve vaginal lubrication, and treat urinary incontinence. However, not all lasers are created equal. The majority of published studies describe the data from CO2 laser therapy, Erbium laser therapy, and radiofrequency. Less is known about the new 1470 nm solid state laser. This is a retrospective study in which 16 women with vaginal dryness were treated with a 1470 nm solid state vaginal laser. All of the patients were cured of vaginal dryness with no pain, bleeding, scarring, or other side effects.

Ultrafast Yb:YAG laser oscillator with gigahertz repetition rate.

We present a SESAM modelocked Yb:YAG solid-state laser providing low-noise narrowband pulses with a pulse duration of 606 fs at a 1.09-GHz repetition rate, delivering up to 2.5 W of average output power. This laser provides access to a new parameter space that could previously not be reached by solid-state lasers and, to the best of our knowledge, is the first modelocked solid-state Yb:YAG laser in the gigahertz regime. This is achieved by introducing a single additional intracavity element, specifically a nonlinear birefringent YVO4 crystal, for soliton formation, polarization selection, and cavity intensity clamping. The isotropic pump absorption in Yb:YAG allows for stable and low-noise operation with multimode fiber pumping. This laser is ideally suited as a seed source for many commercial high-power Yb-doped amplification systems operating at a center wavelength around 1.03 µm. The laser exhibits a high power per comb line of 5.0 mW which also makes it interesting for applications in frequency comb spectroscopy, especially if it is used to pump an optical parametric oscillator. We measure a relative intensity noise (RIN) of 0.03%, integrated from 1 Hz to 10 MHz. Furthermore, we show that the laser timing jitter for noise frequencies >2 kHz is fully explained by a power-dependent shift in the center wavelength of 0.38 nm/W due to the quasi-three-level laser gain material. The narrow gain bandwidth of Yb:YAG reduces this contribution to noise in comparison to other SESAM modelocked Yb-doped lasers.

Nd3+ emission in the garnet structure of LiCa3ZnV3O12 phosphor

Nd3+ doped vanadate phosphors are well known, mainly for their suitability for solid-state laser applications. Garnet structures are also explored for such purposes. LiCa3ZnV3O12 is one of them. Luminescence in this host has not yet been investigated. The luminescence characteristics of LiCa3ZnV3O12:Nd3+ are reported here. Two types of emissions have been observed. The self-activated luminescence could be observed under UV excitation. The characteristic emission of Nd3+ is also observed. Apart from the f–f excitation, an efficient host sensitization of Nd3+ luminescence is observed. The LiCa3ZnV3O12:Nd3+ phosphor showed an intense Near Infrared emission at 1068 nm due to the transition of 4F3/2 → 4I9/2, for 350 nm excitation.

Combined super-Gaussian pump intensity profile model and its application to a solid-state laser

The modeling of a combined super-Gaussian profile distribution for fiber-coupled laser diode beam intensity is investigated in this paper. By fitting the measured beam intensity distribution to the combined super-Gaussian model, the coefficient of determination is better than that of the Gaussian function and super-Gaussian function with order of 2. Applying this theoretical model to the fiber-coupled laser diode end-pumped Nd:GdVO4 laser at 1342 nm, the theoretical calculations are in good agreement with the experimental results.