Laser Crystal Research Articles

Polycrystalline monophenyl solid emitters with amplified spontaneous emission

There are many reports of small molecules exhibiting amplification spontaneous emission laser properties, but there are few reports of single benzene rings exhibiting laser properties while achieving high solid state emission from polycrystalline states. This work takes two very simple organic molecules and constructs an efficient single benzene ring solid state emitter. The crystal laser properties are based on aggregation‐induced emissions (AIE) generated through an excited‐state intramolecular proton transfer reaction (ESIPT).

Proposal and Demonstration of Free-Space Optical Communication Using Photonic Crystal Surface-Emitting Lasers

We propose and demonstrate free-space optical (FSO) communication using photonic crystal surface-emitting lasers (PCSELs). Unlike other types of conventional semiconductor lasers, such as edge-emitting lasers (EELs) and vertical-cavity surface-emitting lasers (VCSELs), PCSELs achieve much larger area single-mode coherent lasing, and this unique feature enables high-power (>watt) and lens-free operations at the same time. To date, these advantages have been recognized to be game changing, especially in light detection and ranging (LiDAR) and laser processing applications. In this work, we show that FSO communication can also benefit from these advantages of PCSELs; more specifically, conventional transmitters that include low-power semiconductor lasers, optical lenses, and fiber-based amplifiers could be replaced with a single PCSEL. Since fiber amplifiers usually consist of bulky components and have low conversion efficiencies, PCSELs can offer more space- and power-saving solutions. Moreover, the narrow beam divergence angles directly obtained from large-area single-mode PCSELs can also eliminate the need for lens systems on the transmitter side. To experimentally verify these potential advantages, we performed FSO transmission experiments based on PCSELs and successfully transmitted 480-MHz and 864-MHz orthogonal frequency division multiplexed (OFDM) signals over 1.1 m using a 500-μm PCSEL in a lens-free transmitter configuration. We believe that PCSELs open new possibilities and choices in FSO communication.

Growth, Thermal, and Optical Properties of a Novel Mid-Infrared Ho:LuYAP Laser Crystal

A novel mid-infrared Ho:Lu0.1Y0.9AlO3 laser crystal with a size of Φ26 mm × 80 mm was grown successfully by the Czochralski method. The crystal structure was characterized in detail by powder and single-crystal X-ray diffractions: Pnma (62) space group, a = 5.3234 Å, b = 7.3517 Å, c = 5.1670 Å, V = 202.22 Å3, and Z = 1. The X-ray rocking curves show that the crystal possesses high crystalline quality. It was observed by a transmission electron microscope that all atoms are neatly arranged and all elements are uniformly distributed. Meanwhile, the refractive index curves from 400 to 3000 nm at three crystalline axes and Mohs hardness were also achieved. The thermal expansion coefficient is 4.382 × 10–6 K–1, and thermal conductivity is 5.872 W·m–1·K–1. Particularly, the maximum phonon energy is only 552 cm–1, as exhibited by the Raman spectrum. Finally, the transmission, fluorescence spectra, and level lifetimes were measured and compared, which provided a basis for subsequent spectral theoretical analysis and laser experiment.

Smart laser controlling mixed-mode state

It is desirable to control the mode states of a laser to stabilize it under the influence of environmental factors as well as to tailor the laser beam. Here, we demonstrate mixed-mode-state control in a photonic crystal surface-emitting laser at the chip level by leveraging the mechanism of mutual injection locking via dynamic control of the current injection distribution. We also demonstrate smart control, in which deep learning is applied to accurately predict the current injection distribution required to achieve a targeted beam pattern owing to manipulation of the mixed-mode state, and vice versa. These results could enable smart laser sources essential for advanced laser processing and additive manufacturing applications.

Thermal effect analysis on cuboid Pr:YLF crystals pumped by blue laser diodes.

Using blue laser diodes (LDs) to pump Pr:YLF crystals can directly realize visible-band laser output. Compared with the traditional frequency doubling and LD direct output method, it has the advantages of simple design, compact structure, and high beam quality. For solid-state lasers, pump-induced thermal effects of gain media are the principal limiting factors for the desired high-power output. In this paper, internal temperature space model distribution of a rectangular cross-section Pr:YLF crystal is established. On this basis, the temperature distribution, thermal stress distribution, and thermal focal length variation of single-end pumped and double-end pumped laser crystals are analyzed. The results are verified by COMSOL simulations and experimental measurements. To our knowledge, this analysis is the first to examine the thermal effect of a rectangular cross-section Pr:YLF crystal, analyzing the limit power that the crystal can withstand, which paves the way for better performances of visible lasers with stable and high-power output.

Limitations of homogeneous and segmented single-crystal compact TEM00-mode Ho3+:YAG laser resonators

We present investigations on output power limitations of near-diffraction-limited compact hbox {Ho}^{3+}:YAG laser resonators employing a homogeneous or segmented laser crystal. An approach for designing a segmented crystal is presented. Maximum output powers of {57.6},hbox {W} and {51.9},hbox {W} are reached with the homogeneous and segmented crystal, respectively, resulting in pulse energies of {1.14},hbox {mJ} and {1.04},hbox {mJ} at a repetition rate of {50},hbox {kHz} in Q-switched operation. Interferometric experiments are conducted to derive the radial temperature profile for both crystals. Simulations based on a split-step beam propagation method are used to model the longitudinal temperature gradient in both crystals.

Graphene oxide saturable absorber for a [formula omitted] passively Q-switched single crystal fiber pulsed laser

In this work, the graphene oxide (GO) samples of different oxidation degree prepared by modified Hummers method were drop-coated on sapphire substrates as saturable absorber (SA). On this basis, this work innovatively combines GO, the excellent SA, with single crystal fiber (SCF), the outstanding laser gain medium, for the first time to achieve 1.03μm passively Q-switched pulsed laser output with the maximum average power of 2.183 W and the repetition frequency of 317.42 kHz, which is, to our knowledge, the largest average power of passively Q-switched SCF pulsed laser output reported so far.

Intra-Cavity Cascaded Pumped 946/1030 nm Dual-Wavelength Vortex Laser Using a Spot-Defect Mirror

Due to their unique properties, vortex lasers have high application value in frontier fields such as optical micromanipulation, super-resolution imaging, quantum entanglement, and optical communication. In this study, we demonstrated a 946/1030 nm Laguerre-Gaussian (LG01) mode dual-wavelength vortex laser by using an intracavity cascade pumped structure and a spot-defect output mirror. Using a coaxial linear cavity structure, the 808 nm laser diode (LD) was used to end-pump the Nd:YAG crystal to generate a 946 nm laser and then use it to directly pump the Yb:YAG crystal in the cavity to generate a 1030 nm laser, and finally a 946/1030 nm dual-wavelength laser came out. By making a spot defect in the center of the output mirror to suppress the oscillation of the fundamental Gaussian mode laser and carefully adjusting the position of the laser crystals, the LG01 mode dual-wavelength vortex laser was output in single handedness. When the pump power was 40 W, the total output was 664 mW (356 and 308 mW at 946 and 1030 nm LG01 mode vortex lasers), and the total optical-optical conversion efficiency was 1.7%; the output power fluctuations of 946 and 1030 nm LG01 mode vortex lasers within 1 h were 3.43% and 3.13%, respectively; the beam quality factors M2 of 946 and 1030 nm LG01 mode vortex lasers were 2.35 and 2.40, respectively. It was proved that the generated dual-wavelength vortex laser had the wavefront phase expiϕ by the self-interference method.

Effect of multidimensional filler hybridization on the mechanical properties of thermoplastic polyurethane composites prepared by selective laser sintering

AbstractThis paper aims to improve the tensile strength and thermal stability performance of selective laser sintered thermoplastic polyurethane elastomer/spherical alumina/graphene oxide/silicon nitride whisker (TPU/Al2O3/GO/Si3N4ws) composites by investigating the synergistic enhancement of fillers with different dimensions, and solving the problem of excessive porosity, material delamination, and low tensile strength during sintering of semi‐crystalline polymer TPU problems. The results show that the synergistic effect of multidimensional fillers leads to the tensile strength of TPU composites up to 12.1 MPa at 8.9 wt% Al2O3, 0.1 wt% GO and 1.0 wt% Si3N4ws hybrid fillers, which is 38.9% higher than that of pure TPU. In addition, the elongation at break of TPU/Al2O3/GO/Si3N4ws composites was maintained at 254%, which still has good toughness. The effect of fillers on the selective laser sintering (SLS) process, thermal stability, melting, and crystallization behaviors of the composites was also investigated in this work. In general, the multidimensional filler compounding synergistically constructing a three‐dimensional network structure has some improvement on the thermomechanical behavior of TPU composites with a fixed mass component addition.

Predicting behavior of photonic crystal fiber lasers using artificial neural networks

Simulating pulse propagation within fiber lasers is a difficult and computationally demanding task, which limits the ability to accurately capture their complex nonlinear dynamics. This paper leverages artificial intelligence (AI) and artificial neural networks (ANN) to predict the output pulse shape parameters for a ring cavity fiber laser, thus avoiding the need for traditional complex numerical calculations and reducing the overall computational cost. This study focuses on a dissipative soliton resonance (DSR) ring cavity fiber laser, incorporating a photonic crystal fiber (PCF) and mode locked by a real saturable absorber. The integration of the PCF into the laser cavity design enhances the control of both dispersion and nonlinearity, allowing for a greater range of output pulse shapes and parameters. The proposed approach demonstrates the effectiveness of artificial neural networks in predicting pulse parameters, and could pave the way for more efficient design and optimization of fiber lasers. The results of the study show that the ANN model can accurately predict the output pulse shape parameters for the DSR ring cavity fiber laser, and thus offers a promising tool for future research in the field.

Switching of lasing direction in reconfigurable chiral photonic crystals

In recent years, the development of lasers using photonic crystals as resonant cavities has emerged and continued to grow. These photonic crystal lasers offer the advantages of reduced threshold levels and compact dimensions. Chiral liquid crystals (CLCs) are self-assembled one-dimensional photonic crystals that enable a wide range of photonic crystal lasers to exhibit broad wavelength tuning capabilities. Our research exploits the uniform standing helix (USH) and uniform lying helix (ULH) states of CLCs as resonant cavities; therefore, the direction of laser emission of CLC lasers can be changed by switching between USH and ULH states. Both USH and ULH lasers in CLCs also exhibit wavelength tuning. The USH laser induces a blue shift in the laser wavelength by dielectric heating, while the ULH laser achieves a redshift of the laser wavelength by applying a vertical electric field to lengthen the helical pitch. Such a reconfigurable chiral photonic crystal laser based on the CLCs provides bidirectional switching of the laser direction while maintaining the ability to tune the wavelength, so it has the potential for use in photonic applications.

Cr:Gd2SrAl2O7: A potential tunable laser crystal with high energy storage capacity

The Cr3+ doped Gd2SrAl2O7 (Cr:GSAO) crystal with tunable light emission has been successfully grown by the Czochralski method for the first time. The Cr:GSAO crystal shows strong absorption on the visible light with an absorption cross-section of 0.53 × 10−19 cm2 at 580 nm for σ-polarization. The crystal field analysis results reveal that Cr3+ ions are accommodated at more than one type of lattice site in GSAO, one with a strong crystal field and the others with an intermediate crystal field. The crystal features long-lived and tunable luminescence. The room temperature luminescence spectrum of Cr:GSAO crystal ranging from 700 nm to 1000 nm is composed of a sharp emission peak and a broad band, which are assigned to the zero-phonon emission and the phonon assisted transitions from 4T2–4A2 of Cr3+. The luminescence lifetime of the Cr:GSAO crystal is 2.82 ms. This indicates that the Cr:GSAO crystal has a potentially good laser performance with excellent energy storage capacity. Our work demonstrates that the Cr:GSAO crystal is a promising candidate for tunable laser gain media.

A new near-infrared broadband laser crystal: Cr3+ doped YScO3

A new near-infrared broadband laser crystal: Cr3+ doped YScO3

Growth and characterization of Fe2+:ZnSe single crystals for tunable mid-infrared lasers

Iron-doped ZnSe (Fe:ZnSe) single crystals were grown by the traveling heater method with the accelerated crucible rotation technique (ACRT) using SnSe as a solvent. The as-grown Fe:ZnSe single crystals were characterized by XRD, Raman, XPS, IR transmission imaging microscope, and the X-ray rocking curve. The results show two kinds of inclusions existing in Fe:ZnSe crystals, i.e. solvent SnSe inclusions, and hexagonal ZnSe inclusions with a wurtzite structure. The inclusions with sizes ranging from 30 to 150 μm were homogeneous distributed with a total concentration of only 2.68 × 102 cm−2. The full width at half-maximum (FWHM) of X-ray rocking curve on (220) diffraction planes was 38 arcsec and the average infrared transmittance exceeded 70%. Furthermore, it was confirmed that the iron ions were successfully incorporated into ZnSe lattice without degrading the crystalline quality, and the bivalence was dominant for iron atoms in Fe:ZnSe crystals, meaning that they are suitable for developing mid-infrared (3–5 μm) gain medium applications.

Ultralow threshold surface emitting ultraviolet lasers with semiconductor nanowires

Surface-emitting (SE) semiconductor lasers have changed our everyday life in various ways such as communication and sensing. Expanding the operation wavelength of SE semiconductor lasers to shorter ultraviolet (UV) wavelength range further broadens the applications to disinfection, medical diagnostics, phototherapy, and so on. Nonetheless, realizing SE lasers in the UV range has remained to be a challenge. Despite of the recent breakthrough in UV SE lasers with aluminum gallium nitride (AlGaN), the electrically injected AlGaN nanowire UV lasers are based on random optical cavities, whereas AlGaN UV vertical-cavity SE lasers (VCSELs) are all through optical pumping and are all with large lasing threshold power densities in the range of several hundred kW/cm2 to MW/cm2. Herein, we report ultralow threshold, SE lasing in the UV spectral range with GaN-based epitaxial nanowire photonic crystals. Lasing at 367 nm is measured, with a threshold of only around 7 kW/cm2 (~ 49 μJ/cm2), a factor of 100× reduction compared to the previously reported conventional AlGaN UV VCSELs at similar lasing wavelengths. This is also the first achievement of nanowire photonic crystal SE lasers in the UV range. Further given the excellent electrical doping that has already been established in III-nitride nanowires, this work offers a viable path for the development of the long-sought-after semiconductor UV SE lasers.

High-Precision Wavelength Tuning of GeSn Nanobeam Lasers via Dynamically Controlled Strain Engineering.

The technology to develop a large number of identical coherent light sources on an integrated photonics platform holds the key to the realization of scalable optical and quantum photonic circuits. Herein, a scalable technique is presented to produce identical on-chip lasers by dynamically controlled strain engineering. By using localized laser annealing that can control the strain in the laser gain medium, the emission wavelengths of several GeSn one-dimensional photonic crystal nanobeam lasers are precisely matched whose initial emission wavelengths are significantly varied. The method changes the GeSn crystal structure in a region far away from the gain medium by inducing Sn segregation in a dynamically controllable manner, enabling the emission wavelength tuning of more than 10nm without degrading the laser emission properties such as intensity and linewidth. The authors believe that the work presents a new possibility to scale up the number of identical light sources for the realization of large-scale photonic-integrated circuits.

Crystal growth and spectral properties of Eu3+-doped La2CaB10O19 single crystals

The invention and commercial application of InGaN/GaN-laser diodes have made it feasible to directly obtain the visible lasing radiation by pumping rare earth (RE) doped laser crystals. Hence searching for new laser crystals with efficient luminescence and applicable optical and physical properties in the visible range is an essential work. Here, the crystal growth and spectral properties of a series of large-size Eu3+ doped La2CaB10O19 (Eu3+-LCB) single crystals with the nominal atomic ratios of 3%, 7%, and 10% have been well studied. High-quality Eu3+-LCB single crystals with the size of 45 × 30 × 17 mm3, was grown by top-seeded solution growth (TSSG) method. The luminescence probe was employed as the tool to identify occupation sites, demonstrating that Eu3+ ions enter into La3+ sites first, then occupy Ca2+ sites after the nominal atomic ratio of Eu3+ ions exceeds 7%. Based on the absorption and emission spectra, the intensity parameters, spontaneous transition probability, radiation lifetime, and fluorescence branch ratio for Eu3+-LCB single crystals are studied with the Judd–Ofelt theory. From the transient spectra, the emission cross-section, fluorescence decay lifetime and luminescence quantum efficiency are deduced, which exhibit the maximum performance at the nominal atomic ratio of 7% Eu3+. Combining the luminescence probe and spectral properties, it can be concluded that Eu3+ doped crystals will have the best spectral properties when Eu3+ occupation at the single La3+ sites reaches the maximum in LCB single crystals, which may be universal for RE-doped crystal with two possible occupation sites. Besides, our work demonstrates that the 7% Eu3+-LCB single crystal may be a promising medium for laser radiation in the visible region in comparison with other Eu3+ doped single crystals.

Novel Nd3+ and Ho3+ co-doped multifunctional CeF3 crystal for laser and magneto-optical applications

In this study, a 1.5 at.% Nd3+ and 0.5 at.% Ho3+ co-doped CeF3 (Nd,Ho:CeF3) single crystal was successfully grown by the vertical Bridgman method. The absorption and fluorescence characteristics of the fabricated crystal were evaluated. The spectroscopic properties of the Nd,Ho:CeF3 crystal were investigated based on the Judd–Ofelt (J–O) theory. The parameters Ω2, Ω4, and Ω6 of Ho3+ were fitted as 0.338 × 10−20, 0.731 × 10−20, and 0.350 × 10−20 cm2, respectively. The fluorescence lifetimes centered at 1064 and 1970 nm for Nd3+ and Ho3+ were 261 and 47 μs, respectively. Notably, the magneto-optical performance of the Nd,Ho:CeF3 crystal was investigated for the first time. The measured Verdet constants of Nd,Ho:CeF3 at 532, 632.8, 1064, 1310, and 1550 nm were 228.0, 154.7, 42.4, 29.1, and 18.5 rad·T−1·m−1, respectively, which were significantly larger than those of pure CeF3 and traditional Tb3Ga5O12. The results demonstrated that Nd,Ho:CeF3 crystals can be applied in both lasers and magneto-optical devices.

946/1030 nm Dual-Wavelength Laguerre-Gaussian (LG01) Mode Vortex Laser Based on Intracavity Cascade Pumped Resonator

In this paper, the 946/1030 nm dual-wavelength LG01 mode vortex laser is obtained by applying the intracavity cascade pumped structure and annular-beam end-pumped method, an innovative and pioneering exploration of the transverse mode of the dual-wavelength laser. First, we demonstrate the oscillation characteristic theoretical model of the dual-wavelength LG01 mode laser, considering the reabsorption effect. Then the length of the laser crystal and the transmittance of the output mirror are simulated and analyzed, respectively, related to the oscillation characteristics of the 946 and 1030 nm LG01 mode vortex lasers. Finally, a 946/1030 nm LG01 mode vortex laser with the same handedness is successfully achieved in our experiment. With 20 W of annular-beam pump power, the output power of 946 and 1030 nm LG01 mode vortex lasers is 0.404 and 0.510 W, the slope efficiency is 3.6% and 6.2%, and the total optical-optical conversion efficiency is 4.6%. At the maximum output power, the fluctuations of output power within 1 h are 4.02% and 4.23%, and the beam quality factors M2 are 2.32 and 2.27, respectively, for 946 and 1030 nm LG01 mode vortex lasers. The wavefront phase exp(iϕ) of the 946/1030 nm dual-wavelength is also proved by the self-interference method.

Comparison of Raman Spectra of Optically Nonlinear LiTaO3:Cr3+ (0.005 wt%) Crystal Laser Excited in Visible (532 nm) and Near-IR (785 nm) Areas

Raman spectra have been excited by the radiation of lasers generatingon in the visible (532 nm) and near-IR (785 nm) ranges in a LiTaO3:Cr3+ (0.005 wt%) crystal. The obtained spectra were compared. Recorded Raman spectra contained bands in the range of <900 cm−1 (first order) up to 2000 cm−1 (second order). The Raman spectra of the second order, excited by near-IR laser radiation, were located against the background of a wide, luminescent halo. The frequency of a single low-intensity band exceeded the exact frequency of an overtone corresponding to the completely symmetric fundamental 4A1(z)LO mode. The attribution of other second-order bands with higher frequencies remains unclear.