mid-IR Laser Applications Research Articles

Recent advancements in femtosecond laser inscribed waveguides in germanate glass for ∼ 2.1 µm laser applications

The realization and integration of high-power and high-speed microscale functionalities on a single chip have been made possible through the revolutionizing field of Photonics. This next generation monolithic technology emphasizes on efficient and cost-effective fabrication of the miniaturized photonic devices with high degree of accuracy. For such monolithic devices small cavity, single frequency laser sources (waveguide lasers) are of immense importance. Multiple techniques have been utilized for the inscription of waveguides in the laser gain media. Femtosecond laser direct writing (FLDW) is an emerging technique for rapid inscription of highly symmetrical and high-quality 3D guiding structures in substrates with low propagation loss. In this article, we present a review on the latest developments around femtosecond laser inscribed waveguides in an emerging germanate glass (in contrast to the commercially available and exotic transparent media) for short to mid-IR laser applications.

Multispectral Anti-Reflection Coatings Based on YbF3/ZnS Materials on ZnGeP2 Substrate by the IBS Method for Mid-IR Laser Applications

A multispectral anti-reflective coating of high radiation strength for laser applications in the IR spectrum for nonlinear ZnGeP2 crystals has been developed for the first time. The coating was constructed using YbF3/ZnS. The developed coating was obtained by a novel approach using ion-beam deposition of these materials on a ZnGeP2 substrate. It has a high LIDT of more than 2 J/cm2. Optimal layer deposition regimes were found for high film density and low absorption, and good adhesion of the coating to the substrate was achieved. At the same time, there was no dissociation of the double compound under high-energy ions.

Crystal Growth, Characterization, and Thermal Annealing of Nonlinear Optical Crystals AgGaGenSe2(n+1) (n = 1.5, 1.75, 2, 3, 4, 5, and 9) for Mid-infrared Applications.

The new quaternary single crystals AgGaGenSe2(n+1) (n = 1.5, 1.75, 2, 3, 4, 5, and 9) have high nonlinear optical property and can be used for mid-IR laser applications in high power. However, only AgGaGe3Se8 and AgGaGe5Se12 have been grown on a large scale and studied in detail. In this work, the AgGaGenSe2(n+1) (n = 1.5, 1.75, 2, 3, 4, 5, and 9) crystals (Φ 20 mm × 40 mm and Φ 40 mm × 100 mm) were grown by the modified Bridgman method. The crystal structure was studied by X-ray diffraction and the Rietveld refinement method. The composition and morphology were characterized by scanning electron microscopy and metallurgical microscopy. The chemical state and vibration modes of surface elements were characterized by X-ray photoelectron spectroscopy and Raman spectra, and the electrical property was investigated by the Hall effect measurement, which indicates that all the single AgGaGenSe2(n+1) crystals are n-type semiconductors. The transmittance of all as-grown AgGaGenSe2(n+1) crystal wafers exceed 65% in the transparent range, and the band gap increases from 2.05 eV for AgGaGe1.5Se5 to 2.14 eV for AgGaGe9Se20. Besides, after being annealed in two different conditions, the wafers show different changes. We discovered a special decomposition phenomenon during the annealing process and found the more appropriate annealing method at last. In addition, the absorption peaks at 4.2, 10, and 14.9 μm of wafers have been nearly eliminated, and the quality of most crystals has been improved.

Burst pulse generation in Cr:ZnSe laser with mid-infrared tunability

We demonstrated a nanosecond pulsed Cr:ZnSe laser with both wavelength tunability and burst pulse operation in the mid-infrared (IR) region. The burst pulse operation of the Cr:ZnSe laser was achieved using a pulse-on-demand Tm:YAG laser as a pump source. The number of pulse shots and the repetition rate in a packet were controlled. A tuning range of 2.32 to 2.56 μm was also achieved using a birefringent filter. Our results show that the pulse-on-demand Tm:YAG laser is an attractive pump source for the burst-pulse-operated Cr:ZnSe laser, which paves the way for various mid-IR laser applications.

Femtosecond laser induced low propagation loss waveguides in a lead-germanate glass for efficient lasing in near to mid-IR

To support the growing landscape of near to mid-IR laser applications we demonstrate a range of low propagation loss femtosecond laser (FSL) written waveguides (WGs) that have achieved guided-mode laser operation in a rare earth (RE) doped lead-germanate glass. The WGs are fabricated in both the athermal and thermal FSL writing regimes using three different pulse repetition frequencies (PRF): 100 kHz (athermal); 1 MHz; and 5 MHz (thermal). The lasing capability of Yb3+ doped lead-germanate waveguides is verified in the near-IR. The refractive index contrast (∆n) for 100 kHz WGs is ~ 1 × 10–4, while for 5 MHz, ∆n increases to ~ 5 × 10–4. The WGs in the thermal regime are less effected by self-focusing and are larger in dimensions with reduced propagation losses. For the 1 MHz repetition rate thermal writing regime we report a low propagation loss WG (0.2 dB/cm) and demonstrate laser operation with slope efficiencies of up to ~ 28%.

Dy3+-doped Ga2S3-Sb2S3-La2S3 chalcogenide glass for mid-infrared fiber laser medium

We report a new Dy3+-doped Ga2S3-Sb2S3-La2S3 (GSLS) chalcogenide glass for mid-infrared (mid-IR) laser applications. With the addition of La2S3 into the previously studied Ga2S3-Sb2S3 glass, the thermal stability of the base glass is significantly enhanced. The glass with the composition 20Ga2S3-75Sb2S3-5La2S3 (mol.%) shows the best thermal stability for fiber drawing, and the glass can be doped with up to 5 mol.% Dy2S3. The Dy3+-doped GSLS bulk glasses and a multimode fiber exhibit intense emissions at 2.95 μm and 4.40 μm. Spectroscopic analyses show that the mid-IR emissions are with high quantum efficiencies and large stimulated emission cross sections, indicating that Dy3+-doped GSLS glass is a promising candidate for mid-IR fiber laser medium.

Role of wavelength in photocarrier absorption and plasma formation threshold under excitation of dielectrics by high-intensity laser field tunable from visible to mid-IR

The development of high power mid-IR laser applications requires a study on laser induced damage threshold (LIDT) in the mid-IR. In this paper we have measured the wavelength dependence of the plasma formation threshold (PFT) that is a LIDT precursor. In order to interpret the observed trends numerically, a model describing the laser induced electron dynamics, based on multiple rate equations, has been developed. We show both theoretically and experimentally that PFT at mid-IR wavelengths is controlled by a transition from weak- to strong-field regime of free carrier absorption. In the case of MgF_2 this transition occurs around 3–4 upmum corresponding to the region of the lowermost PFT. The region of the uppermost PFT is reached around 1 upmum and is governed by an interplay of photoionization and weak-field free carrier absorption which manifests itself in both MgF_2 and SiO_2. The PFT observed in considered materials exhibits a universal dependence on the excitation wavelength in dielectrics. Thus, the presented results pave the route towards efficient and controllable laser-induced material modifications and should be of direct interest to laser researchers and application engineers for prevention of laser-induced damage of optical components in high-intensity mid-IR laser systems.

Homogeneity characterization in AgGaGeS4, a single crystal for nonlinear mid-IR laser applications

Single crystal quality is a key issue for optical applications. Indeed, in optical frequency conversion processes, defects in single crystals can drastically decrease the conversion yield. The study of the quality of an AgGaGeS4 single crystal is presented in this work. Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-Ray Spectroscopy (EDS) was used to perform a chemical analysis mapping of a large size single crystal cut (surface 26 × 20 mm2). Chemical inhomogeneity was found along the crystal growth axes and confirmed by optical characterization showing laser beam perturbations. Compounds volatility, lack of melt homogenization and instability of crystallization front might explain this chemical inhomogeneity. Solutions to improve the crystal growth process and enhance the crystal’s quality are finally proposed.

Polycrystal Synthesis, Crystal Growth, Structure, and Optical Properties of AgGaGe nS2( n+1) ( n = 2, 3, 4, and 5) Single Crystals for Mid-IR Laser Applications.

AgGaGe nS2( n+1) crystal is a series of quaternary nonlinear optical materials for mid-IR laser applications of converting a 1.064 μm pump signal (Nd:YAG laser) to 4-11 μm laser output, but only AgGaGeS4 has attracted the most attention, remaining the other promising AgGaGe nS2( n+1) crystal whose physicochemical properties can be modulated by n value. In this work, AgGaGe nS2( n+1) ( n = 2, 3, 4, and 5) polycrystals are synthesized by vapor transport and mechanical oscillation method with different cooling processes. High-resolution X-ray diffraction analysis and refinement have revealed that all the four compounds are crystallized in the noncentrosymmetric orthorhombic space group Fdd2, resulting in the excellent nonlinear optical property, and the distortion of tetrahedron with the variation of n value causes the discrepancy of physicochemical property. Besides, using the modified Bridgman method, AgGaGe nS2( n+1) single crystals with 15 mm diameter and 20-40 mm length have been grown. We have discussed the structure and composition of AgGaGe nS2( n+1) by XPS spectra and analyzed the three kinds of vibration modes of tetrahedral clusters by the Raman spectra. The Hall measurement indicates that the AgGaGe nS2( n+1) single crystals are p-type semiconductor, and the carrier concentration decreases with the increasing n value. All the transmittances of as-grown AgGaGe nS2( n+1) samples exceeds 60% in the transparent range, especially the transmittance of AgGaGe2S6, is up to 70% at 1064 nm, and the band gap of as-grown crystal increases from 2.85 eV for AgGaGe2S6 to 2.92 eV for AgGaGe5S12. After a thermal annealing treatment, the absorptions at 2.9, 4, and 10 μm have been eliminated, and the band gap changed into the range of 2.89-2.96 eV.

Focus on nanotechnology, lasers, and imaging

Focus on nanotechnology, lasers, and imaging

Crystal growth and characterization of undoped and Dy-doped TlPb2Br5 for infrared lasers and nuclear radiation detection

We report results of the crystal growth and characterization of undoped and Dy-doped TlPb2Br5 for applications in infrared (IR) lasers and nuclear radiation detection. TlPb2Br5 (TPB) was synthesized from commercial starting materials of PbBr2 and TlBr and further purified through a combination of zone-refinement and directional solidification. For doping experiments, 2 wt% of DyBr3 was added to the purified TPB material. Crystal growth of TPB and Dy: TPB was carried out in a two-zone tube furnace by a vertical Bridgman method. Following optical excitation at ∼1.36μm, the Dy: TPB crystal exhibited efficient mid-IR emission bands centered at 2.87μm and 4.35μm with room-temperature lifetimes of 9.5ms and 5.2ms, respectively. The peak emission cross-sections were determined to be ∼0.8×10−20cm2 and ∼0.5×10−20cm2, respectively, which makes Dy: TPB a promising candidate for mid-IR laser applications. Besides its potential as a solid-state laser host, an undoped TPB crystal was also tested for gamma-ray detection. Using Cs-137 and Am-241 sources resulted in energy resolutions for gamma-rays as good as 1–2% (FWHM) at room-temperature under non-optimized conditions.

Preparation, spectroscopic characterization and energy transfer investigation of iron-chromium diffusion co-doped ZnSe for mid-IR laser applications

The spectroscopic characterization and energy transfer mechanism of iron-chromium co-doped ZnSe polycrystalline (Cr,Fe:ZnSe) were reported with dimension of 15mm×15mm×2mm obtained by controlled post-growth thermal diffusion method. The infrared absorption is characterized by a strong broad-band centered at 1770nm which can be attributed to the only spin-allowed transition 5T2→5E within the 3d4 shell of Cr2+ ions. Photoluminescence spectrum shows a relatively strong broad emission band centered at 4.1μm with a width of 0.8μm (FWHM) under 1770nm excitation at room temperature and reveals effective Cr2+→Fe2+ energy transfer process. Room temperature photoluminescence decay about 8μs was measured. All the results indicate that Cr,Fe:ZnSe could achieve laser operation at 3.7–4.5μm via Cr2+→Fe2+ energy transfer using a more convenient laser pump source in the near IR region.

Crystal field engineering of transition metal doped II-VI ternary and quaternary semiconductors for mid-IR tunable laser applications

We report on crystal-field engineering of solid-state laser gain media based on new transition metal (TM) (iron) doped II-VI ternary and quaternary semiconductor materials for middle-infrared (mid-IR) tunable laser applications. Novel ternary and quaternary TM:II-VI materials were fabricated in powder form using thermal annealing of mixtures of commercially available binary powders sealed in evacuated quartz ampoules. These resultant powders were characterized using XRD, micro-Raman spectroscopy, photoluminescence (PL) and PL kinetics. We demonstrate: 1) that this synthesis method enables laser active powder media and is an effective means to fabricate and prototype novel laser active materials, 2) by introducing heavier or lighter ions into the host crystal lattice, it is possible to independently engineer the spectral positions of the absorption and PL band of TM ions in II-VI crystals, and 3) the first time to our knowledge room temperature, mirrorless, random lasing of iron doped Zn0.5Cd0.5Te powders at 5.9 μm.

Control of Melt Decomposition for the Growth of High Quality AgGaGeS4 Single Crystals for Mid-IR Laser Applications

AgGaGeS4 (AGGS) is a promising nonlinear crystal for mid-IR laser applications which could satisfy the lack of materials able to convert a 1.064 μm pump signal (Nd:YAG laser) to wavelengths higher than 4 μm, up to 11 μm. The processing steps of this material are presented in this study. The key issue of AGGS crystal processing is the control of decomposition at high temperature due to the high volatility of GeS2. This study presents solutions to obtain high quality single crystals. AGGS ingots with 28 mm diameter and 70 mm length were grown by the Bridgman–Stockbarger method. The crystals have good homogeneity and high transparency in the 0.5–11.5 μm spectral range, making them suitable for optical experiments. The influence of GeS2 volatility on melt stoichiometry during the AgGaGeS4 processing is outlined, and solutions to improve the crystals quality are presented.

Crystal growth and optical properties of Cr 3+, Er 3+, RE 3+: Gd 3Ga 5O 12 (RE=Tm, Ho, Eu) for mid-IR laser applications

In this paper we report on the optical properties of triply Cr 3+, Er 3+, and RE 3+ (RE=Tm, Ho, Eu) doped Gd 3Ga 5O 12 crystals that were grown by the Czochralski method. Optical absorption, near-infrared (NIR), and mid-infrared (mid-IR) fluorescence spectra were characterized for the fabricated crystals and corresponding luminescence decay measurements under 654 nm excitation were also carried out. Based on the analysis of energy transfer process between Er and RE (RE=Tm, Ho, Eu) ions, the energy transfer efficiency (ETE) values were evaluated, correspondingly. From the spectral data of all the studied crystals, it is observed that the co-doped Cr 3+ ion highly increases the absorption pump power and the three kinds of co-doped RE 3+ ions depopulate the Er: 4I 13/2 energy level effectively. The spectral analysis shows that titled rare earth doped crystals are promising materials for ∼3.0 μm mid-IR laser applications and among them Cr,Er,Eu:GGG is relatively more suitable due to its excellent optical properties compared with others.

Growth and optical spectroscopy of Ho-doped KPb 2Cl 5 for infrared solid-state lasers

Results of the growth and infrared optical properties of Ho-doped KPb 2Cl 5 for potential applications in infrared (IR) solid-state lasers are reported. The investigated crystal was synthesized from commercial starting materials of PbCl 2, KCl, and HoCl 3 followed by several purification steps including normal freezing, zone-refinement, and chlorination. The Ho:KPb 2Cl 5 crystal was subsequently grown by the Bridgman technique. Following optical excitation at ∼0.89 μm, several IR emission bands were observed at room temperature with average wavelengths at 1.07, 1.18, 1.35, 1.65, 2.00, 2.89, and 3.96 μm. The emission at 3.96 μm originated from the 5I 5→ 5I 6 transition of Ho 3+ ions and exhibited a decay time of 5.0 ms at room temperature. Based on a Judd–Ofelt analysis the mid-IR emission quantum efficiency was determined to be near unity, which results in a peak emission cross-section of 0.62×10 −20 cm 2 at 3.96 μm. The obtained spectroscopic results indicate the favorable optical properties of Ho:KPb 2Cl 5 for mid-IR laser applications.

Hot-pressed ceramic Cr2+:ZnSe gain-switched laser

The technology of hot-pressed Cr(2+):ZnSe ceramic preparation is reported. Comparative gain-switched lasing of hot-pressed ceramic and CVD grown Cr(2+):ZnSe samples with slope efficiencies up to 10% and output energies up to 2 mJ were demonstrated. This is a milestone in the development of future large scale mid-IR laser systems based on ceramic TM(2+):II-VI materials. This evolving technology has excellent potential as media for practical low cost, high power mid-IR laser applications.