Ultrafast Laser Applications Research Articles

Structure–luminescence property relationships of Yb3+-Doped Y2Mg3-xCax(SiO4)3 single crystals for 0.95-1.2 μm broadband emissions

This study successfully grew Yb3+-doped Y2Mg3-xCax(SiO4)3 (x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75) (Yb: YCMS) novel single crystals with multiple disordered structures. To the best of our knowledge, this is the first systematic report on the relationship between the luminescence properties (including emission intensity, emission peak position, full width half maximum, and fluorescence lifetime) and the local structure of the luminescent ions based on first-principles calculations. The wide half-height width of emission (103.10 nm@1047 nm) have been realized on the first-grown Yb: YCMS crystals. This study provides a novel solution for designing laser crystals with tunable optical properties. The comprehensive properties of Yb3+-doped YCMS crystals, such as ultra-wide emission bandwidth and high fluorescence lifetime, are promising gain materials for ultrafast laser applications.

Increasing the electric field amplification in the metal-insulator-metal structure with a grating hybrid of bowtie nanotriangle and cylindrical nanodisc

In this paper, the strong electromagnetic coupling between an integrated grating of an array of periodic gold nanodiscs and an array of bowtie nanotriangles placed on layers of a dielectric and a metal has been investigated. The upper layer is periodically created by removing each nanodisk in the array of nanodisks and replacing it with bowtie nanotriangles. The structure for near field radiation with linear polarization at 800nm wavelength is optimized so that it has the highest amount of amplification in the gap space between the tips of the nanotriangle with a minimum value of 188 times and a maximum of 320 times. The simulation results confirm that the huge field enhancement obtained is due to the strong coupling between the LSPR formed in the grating of bowties nano triangle and nanodiscs and the SPPs formed in the metal film. The amount of amplification compared to the array of only nanodiscs (about 32 times) or only bowtie nano triangles (about 120 times) is not only higher, but also the anti-crossing behavior is observed. The high amplification obtained at the mentioned wavelength can be used for laser oscillators with a central wavelength of 800nm, such as titanium sapphire, etc., which has many applications in near-field physics, SERS, and ultrafast lasers.

Polyacrylonitrile enabled soliton mode-locked fiber laser

Exploring novel saturable absorber (SA) materials with superior performance to enable mode-locking operation remains a forefront in ultrafast laser research. In this study, we unveil the potential of polyacrylonitrile (PAN) based SA for ultrafast fiber laser applications. By probing the nonlinear absorption characteristics of PAN SA within the telecommunication band using the balanced twin-detector method, we reveal its substantial modulation depth of 10.7 %. Incorporating PAN SA into the Erbium-doped fiber laser (EDFL) cavity facilitated stable mode-locking operation. The resultant EDFL system produces a conventional soliton pulse train centered at 1568.4 nm wavelength, with mode-locking sustained over a pump power range from 87.2 to 254.1 mW. Moreover, the laser exhibits a pulse duration of 3.64 ps and achieves a maximum pulse energy of 2.04 nJ. These results highlight the efficacy of PAN-based SA, demonstrating properties comparable to established 2D SAs. The implications of this research are pivotal in advancing the application of novel organic polymers in ultrafast lasers.

Multiple soliton operation in Ge2Sb2Te5 saturable absorber based fiber lasers

With the rapid development of fiber lasers, the invention of novel ultrafast modulators based on the new materials is critical for furthering basic research and practical applications of mode-locked fiber lasers. Ge2Sb2Te5 is a kind of phase-change and thermoelectric material. The fields of optical fiber temperature sensors, optical switches, and phase-change memories have all made extensive use of Ge2Sb2Te5. Nevertheless, the performance of Ge2Sb2Te5 is currently unproven in nonlinear optics and ultrafast laser applications. In this study, Ge2Sb2Te5-based saturable absorbers (SAs), were successfully prepared by depositing nanosheets on a tapered optical fiber. Conventional solitons, second-order harmonic mode-locked, and double-, triple-, quadruple-, and quintuple-pulse phenomena at different net dispersions are observed. A conventional soliton was obtained at 166 mW-987 mW with a pulse interval of 102 ns and a signal-to-noise ratio of 59 dB. At 440 mW of pump power, second-order harmonic mode-locked with a 3 dB bandwidth of 3.29 nm was obtained. The experimental results show that Ge2Sb2Te5 has a broad research prospect in designing ultrafast photonic devices in the future by virtue of its low cost, narrow bandgap, high damage threshold and high stability.

Design of three layered step index fiber for femtosecond pulse delivery at 1550 nm wavelength

This paper presents the design and numerical analysis of a step index three-layered fiber optimized for singlemode operation at a wavelength of 1550 nm. The fiber exhibits an extraordinary mode area, measuring 2020 μm², enabling the delivery of ultra-short pulses without distortion. We have used the Transfer Matrix Method for analysis and the Split-Step Fourier Method to solve the nonlinear Schrödinger equation. The study also incorporates considerations for Raman scattering response and self-steepening phenomena in the analysis, enhancing the comprehensive understanding of the proposed step index three-layered fiber for single-mode operation. Demonstrating the propagation of 100-fs pulses with a peak power of 57.7 kW over a 3.4 m length, the fiber maintains a dispersion length-to-nonlinear length ratio of 1 to ensure pulse fidelity. This research offers insights into designing high-performance optical fibers for efficient and distortion-free pulse transmission in ultra-fast laser applications.

Using UV absorption measurements for estimation of laser damage thresholds in ultrafast laser applications

Laser damage for ultrafast pulses is connected to the UV absorption edge via bandgap. This connection may be used to facilitate damage testing and thus coating development. Preliminary results are presented here.

Preparation of large-area uniform PdSe2 film and its application in ultrafast fiber laser

In this work, ultrafast Yb-doped fiber laser was realized using multi-layer palladium diselenide (PdSe2) film as the saturable absorber, which was prepared by simple selenization of palladium film deposited by magnetron sputtering method. The prepared polycrystalline PdSe2 film has a thickness of about 12 nm. At a pump power of 180 mW, the obtained mode-locked fiber laser based on the PdSe2 film has a central wavelength of 1063.75 nm, a pulse width of 615 ps, a repetition rate of 17.66 MHz, and an output power of 4.43 mW, respectively. These results indicate that PdSe2 has great potential in applications of ultrafast lasers.

GHz Compact Laser Enabled by GaSb Nanowires as Saturable Absorbers

Owing to the narrow bandgap and excellent optoelectronic properties, III‐Sb nanowires (NWs) enable efficient optical response from near‐infrared to mid‐infrared, making them ideal candidates for broadband optical modulation. Herein, high‐purity GaSb NWs with controlled density are prepared on the transparent substrates of glasses. The phase purity and crystallinity of as‐prepared GaSb NWs are verified by X‐ray diffraction. Z‐scan and I‐scan techniques are adopted to investigate the nonlinear optical modulation properties, displaying a high modulation depth of 40% (at 1 μm wavelength) for the GaSb NWs with growth time of 30 min. Furthermore, the as‐prepared GaSb NWs are used as the saturable absorber elements in a waveguide laser cavity, demonstrating efficient Q‐switched mode‐locked lasers with a repetition rate of 8.2 GHz and a pulse duration of 31 ps (operating at 1 μm wavelength). All results show the great potential of GaSb NWs for the ultrafast laser and nonlinear optical applications.

Ensuring permanence of optics for ultrafast laser applications

AbstractUltrafast lasers in various applications suffer from short lifetime optics due to high power levels and intense pulses. Typical laser damage testing methods are often limited to short exposure doses, which sometimes do not match real‐life application requirements. To ensure long‐term failure‐free operation, lifetime estimation and low‐loss absorptance testing should be used instead. Low‐absorption dielectric coatings increase the lifetime and lower the total cost of ownership, benefiting the manufacturing, research, and medical sectors.

Transient dynamics of pulsating polarization rotating dual solitons in an ultrafast fiber laser.

The state of polarization is essential for a full description of ultrashort pulses. We experimentally observe the transient vector dynamics of pulsating vector solitons with rotating polarizations in a single-wall carbon nanotube mode-locked fiber laser. We acquire the single-shot polarization evolution of two different dual soliton pulsations using a homemade real-time wavelength-resolved state of polarization measurement system. We identify experimentally two different types of dual-soliton pulsations with longer and shorter pulsating periods respectively, and we find that dispersive-caused wave-caused energy exchange may be the reason for the distinct single soliton polarization evolution in multi-soliton cases. Our results are crucial for understanding the essence of soliton behaviour and developing novel potential applications of ultrafast fiber lasers.

Ultrafast laser volume nanostructuring; a limitless perspective

Ultrafast lasers are now unanimously recognized as processing tools capable of providing utmost precision. This becomes key in the context of material processing as precise feature scales can render a range of new characteristics to the processed materials. These features redesign their properties optically, mechanically, electrically, or from a chemical point of view. Precision is often accompanied by an increase in resolution. The advances in optical beam engineering and irradiation strategies, alongside with controlled material responses, have put in sight the opportunity to reach record small feature sizes, below 100 nm. Is there an intrinsic limit to optical fabrication? What are the new opportunities provided by laser processing on these scales? How one can make light adapt to matter and at the same time control the matter’s response under light on the smallest scales? In this article I intend to provide a brief overview into the latest developments in ultrafast laser volume nanostructuring, fundamentals and applications alike, stressing out the prospective roadmap and the new potential emerging from super-resolved ultrafast smart laser processing technologies.

High-speed optical pulse shaping based on programmable lithium niobate spatial light modulators.

Pulse shaping plays a key role in various applications of ultrafast lasers, such as optical communications, laser micromachining, microscopy, and quantum coherent control. Conventional pulse shaping devices based on liquid crystal spatial light modulators (LCSLMs) or digital micromirror devices (DMDs) only have the shaping speed of several hertz to kilohertz, which is not suitable for applications requiring a high-speed response. Here, we demonstrate a high-speed programmable lithium niobate spatial light modulator (LNSLM) with 128 individual modulation channels and a modulation speed that can reach 1 MHz. Then we establish a high-speed LNSLM-based Fourier-transform (FT) pulse shaper to realize high-speed pulse shaping, and the update rate can reach 350 kHz, only limited by the electric circuit. The proposed high-speed pulse shaper scheme opens new avenues for future applications of ultrafast science, such as microscopic imaging, interaction between light and matter, and spectroscopy.

Ultrastrong Optical Harmonic Generations in Layered Platinum Disulfide in the Mid-Infrared.

Nonlinear optical activities (e.g., harmonic generations) in two-dimensional (2D) layered materials have attracted much attention due to the great promise in diverse optoelectronic applications such as nonlinear optical modulators, nonreciprocal optical device, and nonlinear optical imaging. Exploration of nonlinear optical response (e.g., frequency conversion) in the infrared, especially the mid-infrared (MIR) region, is highly desirable for ultrafast MIR laser applications ranging from tunable MIR coherent sources, MIR supercontinuum generation, and MIR frequency-comb-based spectroscopy to high harmonic generation. However, nonlinear optical effects in 2D layered materials under MIR pump are rarely reported, mainly due to the lack of suitable 2D layered materials. Van der Waals layered platinum disulfide (PtS2) with a sizable bandgap from the visible to the infrared region is a promising candidate for realizing MIR nonlinear optical devices. In this work, we investigate the nonlinear optical properties including third-and fifth-harmonic generation (THG and FHG) in thin layered PtS2 under infrared pump (1550-2510 nm). Strikingly, the ultrastrong third-order nonlinear susceptibility χ(3)(-3ω;ω,ω,ω) of thin layered PtS2 in the MIR region was estimated to be over 10-18 m2/V2, which is about one order of that in traditional transition metal chalcogenides. Such excellent performance makes air-stable PtS2 a potential candidate for developing next-generation MIR nonlinear photonic devices.

High-performance γ-MnO 2 Dual-Core, Pair-Hole Fiber for Ultrafast Photonics

Manganese dioxide (MnO 2 ) is a widely used and well-studied 3-dimensional (3D) transition metal oxide, which has advantages in ultrafast optics due to large specific surface area, narrow bandgap, multiple pores, superior electron transfer capability, and a wide range of light absorption. However, few studies have considered its excellent performance in ultrafast photonics. γ-MnO 2 photonics devices were fabricated based on a special dual-core, pair-hole fiber (DCPHF) carrier and applied in ultrafast optics fields for the first time. The results show that the soliton molecule with tunable temporal separation (1.84 to 2.7 ps) and 600-MHz harmonic solitons are achieved in the experiment. The result proves that this kind of photonics device has good applications in ultrafast lasers, high-performance sensors, fiber optical communications, etc., which can help expand the prospect of combining 3D materials with novel fiber for ultrafast optics device technology.

High-Power Mode-Locked Fiber Laser Using Lead Sulfide Quantum Dots Saturable Absorber

The discovery of different types of nanomaterials including the one-dimensional and two-dimensional materials used as saturable absorbers (SAs) in the applications of ultrafast lasers in recent years increases the ultrafast laser design flexibility and boosts the laser performances. A major research avenue is to explore the potential of nanomaterials for further enhancing the performances of ultrafast lasers in terms of pulse power. To this aim, in this study, using a hot-injection method and drop-coating technology, a fiber-based lead sulfide quantum dot (PbS QD) is synthesized, and its potential as a SA for the generation of higher-power pulses is demonstrated in an erbium-doped fiber laser (EDFL). Experimental results show that the optical damage threshold of the SA is greater than 152.6 mJ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the modulation depth is up to 29.5%. The implementation of the PbS QD as a SA placed in an EDFL enables the laser to yield 2.84 ps ultrashort pulses with an average output power of 59.4 mW at a repetition rate of 6.97 MHz. To the best of our knowledge, it is the highest average output power obtained in ultrafast fiber lasers mode-locked by zero-dimensional QD materials. The results suggest the great potential of PbS QDs in the application that requires the generation of high-power pulses in ultrafast lasers.

γ-MnO2-deposited photonic crystal fiber: Novel photonic devices for multi-state solitons generation

Transition metal oxides, especially MnO2 nanoparticles, are often used as cathode of dry batteries and catalysts. They are also promising materials for ultrafast laser applications due to their strong absorption in visible light and near-infrared wavelength range. In this work, high-concentration MnO2 nanoparticles dispersions embedded in the hole cladding of dual-hole photonic crystal fiber is fabricated as a saturable absorber with a modulation depth of 4 % and a saturation intensity of 25 MW/cm2. Strong MnO2-light interaction occurs due to enhanced evanescent-field strength (over 10 cm) of the SA could enable stable mode locking operation at 1.55 μm region. By inserting a Sagnac fiber filter in the cavity, multi-state solitons are experimentally demonstrated with identical layout, respectively, which greatly improves the versatility of this laser. This study proves that MnO2 nanoparticles possess excellent nonlinear optical properties in the near-infrared band. The simple in-line structure of the proposed nanoparticles-deposited device could pave a way for high power and all-fiber applications of photonics.

The generation and observation of pulses with switchable single/dual wavelengths and tunable bandwidth from a SWNT mode-locked Er-doped fiber laser

Mode-locked pulse outputs with switchable single/dual wavelengths and widely tunable spectral bandwidth are demonstrated by fully exploiting multiple soliton formation mechanisms combining single-wall carbon nanotube, intracavity loss tuning and nonlinear polarization rotation. An isolator with single-polarization fiber pigtails is additionally inserted in a ring fiber laser cavity to introduce polarization-dependent loss modulation for gain profile tuning and nonlinear polarization rotation. Mode-locked by a home-made single-wall carbon nanotube saturable absorber, switchable single/dual-wavelength pulses centered in the 1530- or/and 1550-nm gain regions of erbium-doped fiber are experimentally observed by tuning the intracavity loss to tilt the gain profile. Moreover, the spectral bandwidths of single-wavelength pulses centered in the 1530- and 1550 nm regions could be continuously tuned from 2.4 to 4.0 nm, and 2.7 to 9.0 nm, respectively. Such widely tunable spectral bandwidths are attributed to hybrid mode-locked mechanisms combining the nonlinear polarization rotation and single-wall carbon nanotube. Our results give a deep insight into the well-controlled gain profile tuning and provide a relatively simple setup and method to obtain bandwidth-tunable, wavelength-switchable pulse outputs, showing the potential to meet various requirements of ultrafast laser applications.

High polarizability enhanced EPR, optical linear & nonlinear and electric conductivity: Role of NiFe2O4 nanocrystals in transparent tellurite glass-ceramics

Glass containing magnetic nanocrystals is attractive to obtain high nonlinear and high polarizability. In this study, for the first time, 10 nm cubic NiFe2O4 (NFO) nanocrystals doped tellurite glass was studied in terms of the influence on glass structure, chemical bonds, EPR spectra, optical linear and nonlinearity, complex impedance, and dielectric constant. X-ray diffraction, FT-IR, and X-ray photoelectron spectroscopy revealed the single phase and chemical energy of NFO NCs and NFO- doped glasses. The introduction of NFO modified the glass structure through conversion of TeO4→TeO3, and PO4→PO3 units and producing non-bridging oxygen, which in turn enhanced the polarizability according. EPR analysis revealed the super-exchange interaction between multi-valence states of Ni and Fe ions, contributing to the deformation of NFO lattice and NBO defects in the glass network. The energy band gap of glass was red-shifted by NFO due to the multi-valence states of 3d ions. In addition, the linear and nonlinear refractive index, third-order absorption coefficient, and susceptibility were significantly enhanced because of the high polarizability. 3%NFO glass demonstrated huge third-order nonlinear susceptibility of 9.37 × 10−7 esu and giant DC electric conductivity of 8.84 × 10−4 S/cm at room temperature. The values obtained in the present study were much superior to values from the literature, and the obtained glasses are promising for high ultra-fast laser, supercontinuum generation, and holography applications.

Optical properties of graphene/ZnO spheres/Au heterostructure for enhanced van der Waals saturable absorbers

Van der Waals (vdW) heterostructures offer a promising platform for optimizing and controlling physical properties of a variety of materials and devices, which has attracted extensive attentions in ultrafast photonic applications. Here, a hybrid vdW saturable absorber (SA) based on ZnO sphere heterostructures has been fabricated by transferring the low-temperature hydrothermal method ZnO spheres onto gold mirrors and covering with Au nanoparticles and the graphene layer. In comparison with the ZnO sphere SA, the vdW SA exhibits the stronger emission intensity in the ultraviolet-visible range and the higher optical absorption in the near-infrared range, respectively. Meanwhile, by using the balanced twin-detector technology, a modulation depth of 6.6% has been obtained from vdW SA, which is 2.8 times greater than that of the solo ZnO SA due to the harvest of photons and the transfer of photon-generated carriers in the vdW heterostructure. Based on the hybrid vdW SA, a quite stable Q-switched laser and a mode-locked laser operation with a tunable wavelength range from 1531.4 to 1560.4 nm have been achieved. These results demonstrate a effective strategy for enhancing nonlinear optical properties of SAs and pave a way for developing novel types of SAs for the application of ultrafast lasers.

Comprehensive study on the nonlinear optical response of MoO2 nanosheets in pulsed lasers

Molybdenum dioxide nanosheets (MoO2-NSs), as two-dimensional (2D) materials, have attracted broad attention owing to their high damage threshold, good stability, strong localized surface plasmon resonance (LSPR), affordability, and excellent physicochemical properties. In this work, we successfully synthesized high-quality MoO2-NSs through chemical vapor deposition synthesis method and characterized the morphology and structure of the prepared materials in detail. The saturable absorption characteristics of the MoO2-NSs were measured using Z-scan experiments for the first time. Additionally, the compact Q-switched laser and stable mode-locked laser were successfully realized based on a MoO2-NSs saturable absorber (SA). To the best of our knowledge, this is the first presentation of the application of MoO2-NSs SA in the field of ultrafast photonics. These findings indicate that high-quality MoO2-NSs can be an effective optical modulator for generating high-repetition-rate pulsed lasers, and exhibit promising potential applications in mode-locked ultrafast lasers.