Compact Solid-state Lasers Research Articles

Continuous-wave second-harmonic generation in the far-UVC pumped by a blue laser diode

Far-UVC light in the wavelength range of 200–230 nm has attracted renewed interest because of its safety for human exposure and effectiveness in inactivating pathogens. Here we present a compact solid-state far-UVC laser source based on second-harmonic generation (SHG) using a low-cost commercially-available blue laser diode pump. Leveraging the high intensity of light in a nanophotonic waveguide and heterogeneous integration, our approach achieves Cherenkov phase-matching across a bonded interface consisting of a silicon nitride (SiN) waveguide and a beta barium borate (BBO) nonlinear crystal. Through systematic investigations of waveguide dimensions and pump power, we analyze the dependencies of Cherenkov emission angle, conversion efficiency, and output power. Experimental results confirm the feasibility of generating far-UVC, paving the way for mass production in a compact form factor. This solid-state far-UVC laser source shows significant potential for applications in human-safe disinfection, non-line-of-sight free-space communication, and deep-UV Raman spectroscopy.

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.

Broadband self-pulsed Yb:YAG/YVO4 Raman laser

High repetition rate self-pulsed lasers operating at broadband Stokes wavelengths converted with stimulated Raman scattering effect in a compact Raman solid-state laser dramatically extend potential applications on laser ranging, material processing, optical communication. Here, we report broadband self-pulsed laser oscillation in a continuous-wave (CW) laser diode pumped Yb:YAG/YVO4 Raman laser by slightly tilting YVO4 crystal. Stable self-pulsed laser oscillation is obtained in a pump power regime from 2 W to 2.6 W, and the repetition rate increases from 46.5 kHz to 62 kHz. Self-pulsed Raman laser oscillates in multi-longitudinal-mode, the broadband spectral range covers from 1081.5 nm to 1094.3 nm with a bandwidth of 12.8 nm. At input pump power of 2.6 W, average output power up to 140 mW is obtained for stable self-pulsed Raman laser, the optical conversion efficiency is 5.4%. Self-pulsed Raman laser pulses with pulse energy of 2.3 μJ and pulse width of 3.9 μs are obtained. The peak power is 590 mW. This work provides a new route for developing compact self-pulsed Raman lasers for optical communications, material processing.

Compact continuous-wave solid-state Raman lasers at 707 and 714 nm for laser trapping and cooling of atomic strontium and radium.

Two compact laser sources at 707 and 714 nm are realized efficiently by using a diode-pumped a-cut Nd:YVO4 laser with intracavity stimulated Raman scattering and sum-frequency generation (SFG). The fundamental wave at 1342 nm is generated by the 4F3/2 → 4I13/2 transition in Nd:YVO4 crystal. The Raman Stokes waves at 1496 and 1526 nm were obtained by placing the c-axis of the Nd:YVO4 crystal along the Ng and Nm axes of an Np-cut KGW crystal, respectively. LBO crystals with critical phase matching are used to perform the intracavity SFG of fundamental and Stokes waves. At a pump power of 36 W, the maximum output powers at 707 and 714 nm can reach 2.72 and 3.14 W, corresponding to light-to-light conversion efficiencies of 7.5% and 8.7%, respectively. The developed 707 and 714 nm laser sources are practically useful in laser trapping and cooling related to atomic strontium and radium.

Feasibility of a Low-Power, Low-Resolution Laser-Induced Breakdown Spectroscopy Instrument for Analysis of Nickel Alloys: Quantification of the Major Alloying Elements and Classification.

A simple cost-effective laser-induced breakdown spectroscopy (LIBS) instrument was used for quantification of major elements in several nickel alloys and also sorting them. A compact low-power diode-pumped solid-state laser and a miniature low-resolution spectrometer were assembled for the LIBS instrument. Material properties of the nickel alloys depend mainly on the composition of the major elements, Ni, Cr, and Fe, ranging from a few to ∼60 wt%. The emission peaks at 547.7 nm, 520.4 nm, and 438.1 nm for Ni, Cr, and Fe, respectively, were chosen for this analysis. The analytical performance was found to be enough for the quantification of Ni, Cr, and Fe in the nickel alloys. Limits of detection and accuracy were estimated to be a few weight percent (wt%) and measurement precisions were less than 10% in terms of relative standard deviation. The calibration performance of this intensity-based method was compared with that of the "ratio method" which is used in conventional optical emission spectroscopy analyses. The comparison indicates that the intensity-based method is more appropriate with the low-performance LIBS instrument that detects emission peaks of only a few major elements. Also, multivariate modeling of the six different nickel alloy samples based on the emission peak intensities of Ni, Cr, and Fe was performed using k-nearest neighbors (KNN) and linear discriminant analysis (LDA). The KNN and ordinary LDA models showed 95.0% and 98.3% classification correctness for the separate test data set, respectively. To improve classification performance further, the two-step LDA model was trained. In this approach, the two closest sample classes responsible for the decrease in the classification correctness were separately modeled in the second step to exploit their difference effectively. The two-step LDA model showed 100% correctness in classifying the test objects. Our results indicate that such a low-performance LIBS instrument can be effectively utilized for quantitative analysis of the major elements in the nickel alloys and their rapid identification or sorting in combination with an appropriate multivariate modeling algorithm.

250 fs, 130 mW Laser With Tunable Pulse Repetition Rate From 0.5 to 1.3 GHz

We report a compact ultrafast solid-state laser source with a pulse repetition rate continuously tunable in the range of 0.56–1.23 GHz. The optical cavity design allows a user to vary the repetition rate only by moving positions of two optical components inside the resonator, without a need to exchange components or realignment. The Yb:KYW crystal based cavity emits 250 femtosecond pulses at a central wavelength around 1040 nm, with a self-starting SESAM modelocking. In a robust modelocked operation mode, an average power up to 130 mW is achieved using a stabilized single mode pump diode at a wavelength of 981 nm, while the laser in continuous wave (CW) mode delivers up to 270 mW. Atmospheric air cooling was sufficient for both CW and modelocked laser operation. Quite low noise performance was observed, with carrier frequency SNR higher than 80 dB, although the measurements were taken with the open breadboard setup.

High-temperature terahertz quantum-cascade lasers: design optimization and experimental results

Objectives. Terahertz quantum-cascade lasers (THz QCLs) are compact solid-state lasers pumped by electrical injection to generate radiation in the range from 1.2 to 5.4 THz. The THz QCL operating frequency band contains absorption lines for a number of substances that are suitable for biomedical and environmental applications. In order to reduce the size and cost of THz QCLs and simplify the use of THz sources in these applications, it is necessary to increase the operating temperature of lasers.Methods. To calculate electron transport in THz QCLs, we used a system of balance equations based on wave functions with reduced dipole moments of tunnel-bound states.Results. As a result of the calculations, an original band design with a period based on three GaAs/Al0.18Ga0.82As quantum wells (QWs) and a gain maximum at about 3.3 THz was proposed. Based on the developed design, a THz QCL was fabricated, including the growth of a laser structure by molecular beam epitaxy, postgrowth processing to form strip lasers with a double metal waveguide, as well as an assembly of lasers mounted on a heat sink. The developed THz QCLs was capable of lasing at temperatures of up to 125 K as predicted by the performed calculations. We also studied band designs based on two GaAs/AlxGa1–xAs QWs having varying aluminum contents in the barrier layers (x = 0.20, 0.25, and 0.30).Conclusions. The calculated temperature dependences of the peak gain for two-QW designs with x > 0.2 confirm the possibility of creating THz QCLs operating at temperatures above 200 K. Thus, we have proposed two-QW band designs that outperform existing high-temperature designs in terms of maximum operating temperature.

QCW surface-pumped cryogenically cooled single-slab laser with 1 kW level at 946 nm

We present a kilowatt-level quasi-continuous-wave (QCW) cryogenically cooled 946-nm slab laser oscillator for the first time, to the best of our knowledge. The laser system is based on a double-face-pumped large-size single-slab Nd:YAG design, delivering a record-high average power of 1.06 kW without additional amplification. This laser oscillator operates at repetition rate of 400 Hz with a pulse duration of 175 µs, resulting in a single pulse energy of 2.65 J. To the best of our knowledge, these results represent the highest output power and pulse energy for any all-solid-state 946-nm laser ever reported to date. Our scheme paves a new path for the development of the compact high-power solid-state 946-nm laser.

Intracavity losses effect on mode-locking in a waveguide laser with graphene saturable absorber

A single-wavelength compact diode-pumped solid-state laser based on a single-mode waveguide with a diameter of 20 µm and graphene saturable absorber is presented in this work. The total reflection coefficient of the intracavity interferometer has a significant effect on the level of intracavity losses. By accurate controlling the intracavity losses a stable continuous wave passive mode-locking at wavelength of 1064 nm with a pulse repetition rate of 9.5 GHz was obtained.

150 kHz, 300 ps green laser frequency doubled from a linearly polarized passively Q-switched Nd:YAG/Cr4+:YAG microchip oscillator and a Nd:YVO4 amplifier

We report the design and performance of a compact solid-state green laser capable of producing a 300 ps pulse width (PW) at a pulse repetition rate (PRR) of 150 kHz. The green laser was comprised of a thermally bonded [111]-cut Nd:YAG and [110]-cut Cr4+:YAG microchip, a Nd:YVO4 crystal, and a hydrothermal grey-track resisted KTP crystal, serving as the oscillator, amplifier and nonlinear frequency converter, respectively. The optimal working conditions for efficient laser amplification and nonlinear frequency conversion were studied by numerical solving the rate equations and coupled wave equations, respectively. Experimental setups were constructed thereafter according to the simulated results. Stable single-longitudinal-mode-operated, linearly polarized (LP) pulses with PW of ∼ 350 ps, PRR of ∼ 150 kHz, and polarization extinction ratio > 13 dB were obtained from the oscillator. The average power was boosted from 285 mW to 1.8 W by the amplifier and then frequency doubled to 532 nm with an average power of 970 mW, resulting in a shorter PW of ∼ 300 ps. The long term power stability of 0.63% (rms) was measured in 200 min indicating its great potential for practical Lidar applications. To the best of our knowledge, these results are among the highest PRR from a LP Nd:YAG/Cr4+:YAG based green laser with PW ≤ 300 ps. The design procedure has also provided an effective way towards the construction of compact solid-state laser systems with oscillation, amplification, and nonlinear frequency conversion units.

Multivariate stoichiometric analysis of gadolinium-doped ceria using low-power low-resolution laser-induced breakdown spectroscopy

Gadolinium-doped ceria (GDC) is a functional ceramic material used for the electrolytes and electrodes in solid oxide fuel cells (SOFCs). As the more SOFCs are used in power generation, a demand on the practical and reliable analytical methodology for GDCs would increase further. In this work, we investigated feasibility of the laser-induced breakdown spectroscopy (LIBS) instrument assembled with a compact low-power diode-pumped solid-state laser and a hand-held low-resolution spectrometer for stoichiometric analysis of GDCs. LIBS uses laser ablation sampling that greatly simplifies the sample preparation process by removing acid digestion, high temperature treatment, and further dilution indispensable for conventional elemental analyses. In the observed wavelength region of 397 – 450 nm, Gd and Ce poured out rich emission lines and those were unable to be resolved by the low-resolution spectrometer. However, the characteristic spectral features of Gd and Ce were successfully extracted from the unresolved spectra and well correlated with the mole fractions of Gd in GDCs by means of partial least squares-regression (PLS-R). Our results indicate that the low-performance LIBS instrument and PLS-R calibration can be a cost-effective practical technique for stoichiometric analysis of GDCs.

Intra-oscillator broadband THz generation in a compact ultrafast diode-pumped solid-state laser.

We demonstrate broadband and powerful terahertz (THz) generation at megahertz repetition rate based on intra-oscillator optical rectification (OR) in gallium phosphide (GaP). By placing the nonlinear crystal directly inside the cavity of a Kerr-lens mode-locked ultrafast diode-pumped solid-state laser (DPSSL) oscillator, we demonstrate a compact and single-stage THz source. Using only 7 W of diode-pump power, we drive OR in a GaP crystal with 22 W of average power at ∼80 MHz repetition rate. In a first configuration, using a 0.3-mm-thick GaP and 105 fs driving pulses, we generate up to 150 µW of THz radiation with a spectrum extending to 5.5 THz. In a second configuration allowing for sub-50-fs pulse duration, we generate up to 7 THz inside a 0.1-mm-thick GaP crystal. This performance is well suited for THz time-domain spectroscopy and THz imaging. Intra-oscillator THz generation in sub-100-fs DPSSLs is a promising way to scale down footprint, complexity and cost of powerful broadband THz sources.

Structured laser beams: toward 2-μm femtosecond laser vortices

Structured ultrashort-pulse laser beams, and in particular eigenmodes of the paraxial Helmholtz equation, are currently extensively studied for novel potential applications in various fields, e.g., laser plasma acceleration, attosecond science, and fine micromachining. To extend these prospects further, in the present work we push forward the advancement of such femtosecond structured laser sources into the 2-μm spectral region. Ultrashort-pulse Hermite– and Laguerre–Gaussian laser modes both with a pulse duration around 100 fs are successfully produced from a compact solid-state laser in combination with a simple single-cylindrical-lens converter. The negligible beam astigmatism, the broad optical spectra, and the almost chirp-free pulses emphasize the high reliability of this laser source. This work, as a proof of principle study, paves the way toward few-cycle pulse generation of optical vortices at 2 μm. The presented light source can enable new research in the fields of interaction with organic materials, next generation optical detection, and optical vortex infrared supercontinuum.

Q-switched mode in laser ceramics with Cr4+ for technological surface cleaning

A compact solid-state laser based on a Nd:YAG (1 at. %) ceramic active media in the Q-switched mode was studied. Ceramic YAG elements with different concentrations (0.1 to 1 at.%) of Cr4+ doping were used as a Q-switches, 50 to 500 ns pulses were registered with the high energy single pulse. Transparent ceramic obtained by thermosetting sintering. A laser scheme is proposed with a pulse duration and energy setting that contains a composite element for combining the properties of the studied samples of transparent ceramics in one volume. This scheme allows you to implement a compact laser to clean the surface of various materials (glass, concrete, plastic, steel, etc.) from contamination.

Compact solid-state organic laser with fine and broadband wavelength tunability.

An organic dye-doped polymer laser with a novel wavelength-tuning mechanism is proposed. This device is a vertical cavity surface-emitting laser realized by using a couple of distributed Bragg reflectors (DBRs), on which a dye-doped polymer thin film and a polydimethylsiloxane film are deposited individually. One of the DBRs is electrically driven to vary the effective cavity length. Under the optical excitation, tunable lasing operation with high stability can be achieved when immersion oil is used for the refractive index matching in the cavity. Since the device operation mechanism proposed here is quite simple, it is promising for designing a compact laser device with wide, precise, and electrically driven wavelength tunability.

High-order cylindrical vector beams with tunable topological charge up to 14 directly generated from a microchip laser with high beam quality and high efficiency

Large topological charge optical vortex beams carrying orbital angular momentum have potential applications on optical trapping, optical communication with high capacity, quantum information processing. However, the beam quality is degraded in vortex beams generated with spiral phase plates or resonator mirrors with defect spots and optical conversion efficiency in solid-state lasers is sacrificed by controlling the loss of resonator. It is a big challenge for generating high beam quality, high-order cylindrical vector beams with large topological charge in compact solid-state lasers. Here, high-order cylindrical vector beams [Laguerre-Gaussian (LG) modes with zero degree and order of l, LG0,l] with tunable topological charges up to 14 have been generated in an annular beam pumped Yb:YAG microchip laser by manipulating the pump power-dependent population inversion distribution. Efficient performance with optical efficiency of 17.5% has been achieved. The output power is 1.36 W for a vector-vortex laser with 14 topological charges. The pump power dependent wavelength tunable and dual-wavelength laser oscillation in vector-vortex beams has been observed by controlling the reabsorption loss at 1030 nm. Wavelength tunable, dual-wavelength (1030 and 1050 nm) laser oscillation has been achieved for vector-vortex beams with topological charges of 8, 9, and 10. The laser beam quality factor M2 close to the theoretical value (l + 1) has been achieved for LG0,l vector-vortex beams with tunable topological charges up to 14. This work provides a new effective method for generating large topological charge high-order cylindrical vector beams in solid-state microchip lasers with high efficiency and high beam quality.

Feasibility of Quantitative Analysis of Magnesium and Calcium in Edible Salts Using a Simple Laser-Induced Breakdown Spectroscopy Device.

Feasibility of a simple laser-induced breakdown spectroscopy (LIBS) device has been investigated for the analysis of Mg and Ca in edible salts. The LIBS spectrometer was assembled with a compact low-power diode-pumped solid-state laser (DPSSL) and a non-gated low-resolution handheld spectrometer. A simple sampling process was employed for on-site application. A piece of filter paper was dipped in the aqueous solution of a sample salt and dried for analysis using LIBS. Maintaining the sample surface height at the optimum position was critical to generate plasmas persistently due to the low pulse energy of the DPSSL. The varying height of the filter paper surface was monitored and compensated, while the sample stage was translated to collect spectra from different positions. The variation of line intensities of Mg and Ca could be attributed to the inhomogeneous distribution of dry residues. To correct this, the peak that consists of the Na(I) and C(II) lines at 568 nm was employed as a reference signal for intensity normalization of the analyte Mg(II) and Ca(II) lines. For edible salt products, the normalized Mg(II) and Ca(II) line intensities could be well correlated with the concentrations of Mg and Ca determined using inductively coupled plasma optical emission spectroscopy. Our results indicate that a simple LIBS device in combination with the simple sampling method is promising as an on-site salt quality assessment methodology.

High-power dual-color yellow–green solid-state self-Raman laser

A compact dual-color solid-state self-Raman laser with adjustable power-ratio between yellow and green emissions is demonstrated by using a specially coated Nd:YVO4 crystal. The Nd:YVO4 crystal is coated to replace a cavity mirror for minimizing the cavity losses and to reflect the backward green–yellow emission for avoiding the absorption. Two different lithium triborate (LBO) crystals are employed to produce the SHG of the 1176 nm Stokes field and the 1064 nm fundamental wave for the yellow and green emissions. The temperature of the LBO crystal for yellow generation is controlled at the optimal phase-matching to maximize the efficiency. The temperature of the LBO crystal for green generation is precisely varied to adjust the power-ratio between the yellow and green emissions. At the temperature for balanced emissions, both of 532 nm and 588 nm output powers can simultaneously achieve 4.0 W at a pump power of 31.6 W.

Compact solid-state waveguide lasers operating in the pulsed regime: a review [Invited

Over the last years, there has been tremendous progress with compact pulsed lasers based on various solid-state gain media, such as crystals and glasses doped with laser-active ions. With the integration of increasingly diverse saturable absorber materials, these small sources are capable of delivering stable pulses with durations as short as femtoseconds and repetition rates exceeding 10 GHz. These promising sources are known as solid-state waveguide lasers, which have become synonymous with miniaturization, integration, and functionality. This article overviews the progress in the development of passively Q-switched and mode-locked solid-state waveguide lasers employing diverse saturable absorbers. The most commonly used laser configurations, state-of-the-art waveguide fabrication techniques, and experimental demonstrations of pulsed waveguide lasers are summarized and reviewed. Selected well-noted topics, which may shape the future directions in this field, are also presented.

Third order nonlinearity and optical limiting behaviors of Yb:YAG nanoparticles by Z-scan technique

The present report explores third order nonlinear optical behavior of phase pure Yb3+:YAG nanoparticles for the first time by Z-scan technique. The measurement was carried out using diode pumped continuous wave (CW) Nd:YAG laser at 532 nm. The Yb:YAG nanoparticles exhibit characteristic near-infrared (NIR) emission at 1030 nm under 940 nm excitation. The nanoparticles exhibit high nonlinear refractive index (n2 = 8.649 × 10−8 cm2/W) and low nonlinear absorption coefficient (β = 0.109 × 10−4 cm/W) giving an appreciable figure of merit (FOM) of ∼74.50. The excitation power (8.2–10.5 W cm−2) dependent emission spectra were recorded to study exchange energy interaction of Yb3+ ions with YAG host lattice. By utilizing the nonlinear refractive index ‘n2’ from Z-scan measurement, thermo-optic coefficient (dn/dt) was calculated to demonstrate Yb3+:YAG nanomaterial for high power compact solid state laser gain amplifier systems.