LG1,1 vortex carrying orbital angular momentum and elliptical polarization has unique intensity distribution, and finds many applications on high-resolution imaging, manipulation and trapping particles, and quantum information technologies. Here, 1-mm-thick, 15 at.% Yb:YAG crystal and 2-mm-thick a-cut YVO4 crystal are used to construct a Raman microchip laser (RML). By setting the annular pump beam focus spot 0.1 mm inside Yb:YAG crystal, stable LG1,1 vortices operating at 1050/1076 nm dual-wavelength, and 1076 nm Raman laser wavelength are obtained. The LG1,1 vortex oscillates in Yb:YAG/YVO4 RML when the input pump power (Pin) is higher than 3.4 W. Transition from LG1,0 mode to LG1,1 vortex occurs at Pin = 3.4 W. The physical mechanism of forming LG1,1 vortex in the Yb:YAG/YVO4 RML is designed spatial distribution of inversion population, and Raman laser conversion induced spatially changeable output loss for intracavity fundamental laser field. The Raman laser power of LG1,1 vortex increases exponentially with Pin, and 130 mW is obtained at Pin = 5.2 W. High beam quality and elliptical polarization are achieved for LG1,1 vortices operating at 1050/1076 nm dual-wavelength, and 1076 nm Raman laser wavelength. This work paves a road for developing compact Raman lasers for generating high beam quality elliptically polarized LG1,1 vortices, which meets requirements for various potential applications.

Conventional inertia-free multiphoton microscopy (MPM) suffers from depth-dependent degradation of lateral and axial resolution during axial scanning due to defocus-induced aberrations. We introduce truncated non-diffracting beams (tNDBs), generated by segmenting a Bessel beam into multiple axial sections with equalized focal lengths, enabling depth-invariant 3D focusing in laser-scanning MPM. The tNDB maintains constant lateral (~540 nm) and axial (~6 µm) resolutions across a ~29-μm depth range. The method is validated using bead phantoms and mouse brain tissue, consistently revealing sharper structures across depth. tNDBs provide an inertia-free and aberration-robust solution for fast volumetric MPM, enabling constant-resolution 3D imaging without modifying the detection geometry.

Imaging neural structures deep in brain tissue is central to understanding brain function, yet remains fundamentally limited by strong optical scattering and the requirement for accurate three-dimensional (3D) optical sectioning. Laser-scanning microscopy is a promising technique for brain imaging; however, maintaining excitation focus integrity in scattering media while preserving axial confinement poses a persistent photonic challenge. Here we introduce the optical pin, an ultrashort excitation regime engineered at the angular-spectrum level to address this limitation. By broadening the transverse angular bandwidth of a Bessel-type field while preserving its conical momentum-space architecture, the optical pin introduces a controlled longitudinal wave-vector spread that compresses the axial interference length to the micrometer scale, restoring Gaussian-like sectioning without sacrificing multi-angle interference. This excitation design yields substantially enhanced imaging performance, including similar to 1.5-fold contrast improvement and similar to 2.6-fold increased robustness to scattering. We validate the approach across transparent, scattering, and biological specimens, including bead phantoms, C. elegans, and mouse brain tissue. As a system-level excitation strategy, the optical pin is readily compatible with existing laser-scanning microscopy platforms and is particularly suited for scattering-limited brain imaging.

High peak power lasers with transverse intensity distribution in the form of Ince-Gaussian modes with order p and degree m (IG(p,m)) have potential applications in manipulating microparticles, forming optical vortex arrays, optical trapping, and optical tweezers. It is a challenge to generate high-order IG mode laser pulses in passively Q-switched (PQS) solid-state lasers. Here, aYb:YAG/Cr4+:YAG PQS microchip laser pumped with a tilted high-power quasi-continuous-wave laser diode is demonstrated for generating high-order IG mode laser pulses with p and m up to 9. Oscillation of IG modes in the PQS microchip laser strongly depends on the tilted angle of the pump beam. The peak power over 50 kW is achieved for all the p,p IG(p,p)(o)(p = 1, ..., 9) mode pulses generated in the PQS microchip laser. In addition, all the IG(p,p)(o )mode (p = 1, ..., 9) o pulses have a pulse energy over 54 mu J and a pulse width of about 1 ns.

One-dimensional (1D) vortex arrays (VAs) carrying multiple phase singularities arranged linearly have significant promise for applications in flexible multiparticle manipulation, assembly micro-processing, and optical communications. The broadening of their lasing range and wavelengths significantly enhances their versatility for practical applications. However, 1D-VAs generated in solid-state lasers with external cavity methods suffer from instability and inefficiency. Here, we present a simple efficient approach for achieving stable broadband 1D-VAs with phase singularities up to five in a compact Yb:YAG/KTP Raman laser pumped with a tilted beam. The optical vortices of 1D-VAs are controlled by adjusting the incident pump power (P-in). All 1D-VA Raman lasers oscillate within a pump power range of over 1 W. For the 1D-VA with five singularities, the maximum output power reaches 230 mW at P-in = 6.4 W, and the optical conversion efficiency is 3.6%. The 1D-VA with five singularities oscillates in 59 longitudinal modes and covers a laser spectral range of 14.6 nm. The 1D-VA with five singularities operating from 1086.1 to 1100.7 nm generated in Yb:YAG/KTP Raman laser opens a new window for developing compact Raman lasers to generate 1D-VAs with multiple singularities for assembly manipulation of microparticles and micro-processing.

Laguerre-Gaussian (LGp,l) petal-like beams possess significant application potential in fields including microparticle manipulation, microscopy imaging, and quantum communication. However, the direct generation of high-beam-quality LGp,l modes within a laser cavity remains a considerable challenge. In this work, high-order LG0,l and LG1,l petal-like modes are directly generated from an Yb:YAG/YVO4 Raman microchip laser (RML) pumped by an annular beam. To excite LG1,l modes in the RML, the beam waist of the focused pump spot is set to 90 mu m, and its position is fixed 0.2 mm away from the entrance surface of the Yb:YAG crystal. When the input pump power (Pin) increases from 2.8 W to 4.7 W, LG0,l (l = 3, 4, 5, 6) petal-like modes are excited in the RML. These LG0,l (l = 3, 4, 5, 6) petal-like lasers achieve simultaneous dual-wavelength oscillation at the 1050 nm fundamental wavelength and 1076 nm Raman wavelength. When Pin exceeds 4.7 W, the RML switches to oscillate in LG1,l petal-like modes, with the order l increasing from 7 to 9 as Pin rises. In this regime, the LG1,l petal-like modes oscillate exclusively at the 1076 nm Raman wavelength. An output power of 160 mW is achieved for the LG1,9 petal-like Raman laser at Pin = 6.2 W. Characterization confirms that the generated LG0,l and LG1,l petal-like modes possess high beam quality, with the measured M2 factors agreeing well with the theoretical values, and exhibit intrinsic elliptical polarization. The high-beam-quality elliptically polarized LG1,l (l = 7, 8, 9) petal-like Raman lasers demonstrated in this compact Yb:YAG/YVO4 RML extend the application scope of highorder LGp,l petal-like beams to microparticle manipulation, micro-assembly machining, and quantum information processing. Furthermore, the proposed scheme provides a simple and effective approach for realizing compact high-order LG petal-like lasers.

Optical vortices carrying orbital angular momentum with large topological charges have wide applications on optical communication, high capacity storage, high resolution imaging. Hermite-Gaussian (HG) mode lasers have been widely used to convert optical vortices with astigmatic mode converter. Here, high-order HG(m,0 )mode microchip laser has been demonstrated by manipulating gain distribution inside Yb:YAG gain medium. HG(m,0) mode lasers with m tunable from 0 to 21 have been generated by adjusting the distance between x-axis focal spot of single-emitter laser diode and Yb:YAG crystal thin plate (Delta z). At a constant pump power of 4.55 W, output power decreases from 977 mW for TEM00 mode laser to 652 mW for HG(21,0) mode laser as Delta z increases from 2.9 mm to 10.8 mm. Output power of 750 mW and optical conversion efficiency of 15 % are achieved for HG(24,0) mode laser. HG(m,0) mode lasers oscillate in multi-longitudinal-mode, and laser wavelength is kept constant independent on m. Optical vortices with tunable topological charge up to 24 are converted from high beam quality HG(m,0) mode lasers with an astigmatic mode converter. By manipulating pump beam distribution of singleemitter laser diode, microchip laser is a solid platform for efficiently generating high-order HG(m,0) lasers and conversion to desired optical vortices.

A compact Yb:YAG/KTP Raman laser is constructed by using a broadband Yb:YAG crystal and multiple Raman shift lines of GTR-KTP crystal. By utilizing the multiple Raman shift lines around 200-400 cm(-1) in GTR-KTP crystal, broadband multi-longitudinal-mode cascade Raman lasers have been experimentally demonstrated and theoretically analyzed for the first time. When the incident pump power (Pin) reaches to 1.5 W, 213, 267 and 311 cm- 1 Raman shift lines are utilized for generating cascade Raman laser including first-order (1st) Stokes laser covering from 1.08 to 1.1 mu m, and second-order (2nd) Stokes laser covering from 1.12 to 1.13 mu m. The central wavelengths of 1st Stokes laser are 1084, 1091 and 1096 nm, while central wavelengths of 2nd Stokes laser are 1124 and 1129 nm. As the P in is higher than 2.5 W, the new Raman conversions occur based on the Raman shift lines of 267, 379 and 400 cm- 1 with relatively high Raman gain. Moreover, the laser spectra of 1st and cascade 2nd Stokes lasers are connected. At P in of 3.2 W, a broadband Raman laser oscillates with a 50 nm bandwidth covering from 1084 to 1134 nm. 146 longitudinal modes with different intensities oscillate simultaneously. The maximum output power of 0.6 W is obtained with an optical conversion efficiency of 18.8%. This work paves a practical way to develop compact and effective broadband cascade Raman laser source for generating visible laser oscillating at yellow-green gap region with frequency mixing generation.

Structured light fields in the form of Hermite‐Gaussian modes with 2D tunable indices of m and n (HG m , n ), and optical vortices in the form of Laguerre‐Gaussian modes with radial index p and azimuthal index l (LG p, l ) are extremely needed for applications on optical communications, optical trapping, and quantum information processing. Here, high‐order HG m , n modes and LG p , l optical vortices with 2D tunable indices are generated in a gain‐manipulated Yb:YAG/YVO 4 Raman microchip laser (RML). The gain distribution is manipulated by controlling the separation between Yb:YAG crystal and the focus spot of the y ‐axis of the laser diode (Δz). HG m , n modes with 2D tunable indices of m up to 14 and n up to 2 are generated in Yb:YAG/YVO 4 RML by setting Δz = −0.5, −4.1, and −6.6 mm. The power of HG 14,0 , HG 7,1 , and HG 6,2 mode lasers are 0.49, 0.31, and 0.34 W under pump power of 3.1 W, and corresponding optical efficiencies are 11%, 7%, and 7.7%. LG p , l optical vortices with p = 0, 1, 2, and l up to 14 are converted from HG m , n mode lasers with a conversion efficiency of over 90%. High beam quality HG m , n modes, and LG p , l optical vortices with 2D tunable indices oscillating at Stokes wavelengths dramatically extend their applications.

Photoacoustic microscopy (PAM) is a label-free and noninvasive imaging tool for monitoring blood vessels and lipids in vivo. However, simultaneously imaging both indicators has been challenging with a single laser source. Here, we report a compact all-crystal passively Q-switched solid-state laser that simultaneously generates 532 nm and ~1.2 μm wavelengths for blood and lipid contrasts in PAM. The laser leverages both second-harmonic generation (SHG) and stimulated Raman scattering (SRS) in nonlinear crystals. It produces ~2 ns pulses at ~16 kHz repetition rate, satisfying high-performance PAM requirements. We demonstrate dual-wavelength PAM imaging of a USAF1951 test target, blood (hemoglobin), butter, and mouse mesenteric fat. This 532/1176 nm source provides a new, to the best of our knowledge, option for multi-contrast PAM, with potential utility in clinical applications.

In photoacoustic imaging (PAI), a nanosecond laser with the controllable pulse width (PW) and pulse number (PN) benefits variable photoacoustic (PA) frequencies and nonlinear excitations. Here, we report a compact (1-mm-long cavity) gainswitched laser that directly generates tunable PW (18-110 ns) and PN (1-4) with pulse intervals (236-553 ns), as well as adjustable repetition rates (5-35 kHz), utilizing the relaxation oscillation effect. We showcase the tunable PW excitation and the PA enhancement of 33.9% under multi-pulse excitation. The promising performance suggests that the laser can be flexibly applied in functional and nonlinear PAI systems.

Miniaturization of photoacoustic microscopy(PAM)to portable and wearable levels requires special design of scanning,detection,acquisition,and excitation units.Now the first three can be minimized to gram and milli-meter levels,but the excitation sources usually remain bulky and also face different challenges,including low pulse energy,wide pulse width,limited wavelength,or high cost.Here,we propose a high-performance laser source specially designed for a miniature PAM system,that is,the pulse-pumped passively Q-switched solid-state laser(PQS-SSL).Its kilohertz repetition rate,nanosecond pulse width,microjoule pulse energy,and UV to NIR spectra are exactly within the requirements of functional PAM imaging,together with the merits of millimeter scale and low cost,originating from the all-crystal-based configuration.The pulsed pump technique empowers the laser with frequency lock and trigger-in ability for system synchronization,overcoming the conventional free-running drawbacks,and the senior multi-pulse pump is also feasible to further compress the laser size and cost.We showcase its PAM performance on the USAF1951,carbon fiber,zebrafish,and lipid(wavelength extension to～1.2 μm).The novel,to our knowledge,pulse-pumped PQS-SSL is not only promising for general PAM,but also paves the way to develop miniature PAM systems,such as hand-held or brain-wearable modalities.

We significantly enhance the lateral resolution of a two-photon imaging system by shortening the axial extent of the Bessel beam. Under identical numerical aperture conditions, the Bessel beam achieves a lateral resolution of 320 +/- 25 nm, indicating a 41% improvement over the 547 +/- 22 nm resolution obtained with a conventional Gaussian beam. This enhanced resolution was further validated by imaging two adjacent 100-nm fluorescent microspheres. The proposed approach effectively improves imaging resolution without modifying the optical hardware, offering a new strategy for high-resolution and depth-flexible nonlinear optical imaging.

Nonlinear photoacoustic microscopy (PAM) usually requires dual-pulse excitation. Current approaches to realize dual-pulse laser train are indirect, mainly based on beam combinations. Here, we report a compact (∼5-cm-long cavity) laser source that directly outputs controllable nanosecond (∼34 ns) dual pulses, including the tunability of repetition rate (0-20 kHz), time delay (5-30 µs), and relative intensity ratio (20-500%), perfectly matching the requirements of nonlinear imaging in PAM. The single pulse energy is achieved up to ∼95 µJ. We showcase the nonlinear PA performance with this laser source in typical Grüneisen-relaxation-based applications with imaging contrast enhanced by 8 dB. The promising performance indicates that this dual-pulse laser can readily be applied to nonlinear PAMs, especially for portable applications.

Optical vortex-arrays with multiple singularities have potential applications in high-capacity optical communication, particle manipulation and high-resolution measurement. Vortex-arrays with desirable spatial distribution of singularities and operating at new wavelengths further extend their applications. Here, an optical vortex-array with four singularities has been achieved in a Yb:YAG/YVO4 Raman microchip laser pumped with a tilted annular beam. Stable vortex-array with four singularities distributed in a square shape is achieved with simultaneous oscillation of frequency-degenerate modes in an asymmetric resonator with stimulated Raman scattering effect. Stable vortex-array with four singularities oscillates in a wide incident pump power (P-in) range from 2.8 to 5.7 W. The highest output power is 0.34 W with an optical efficiency of 5.9% for vortex-array with four-singularities at P-in = 5.7 W. The Raman laser oscillates in TEM00 mode at P-in < 2.8 W. Vortex-array with four singularities becomes unstable at P-in > 5.7 W and vortex-array with six singularities oscillates at P-in > 6 W. The highest Raman spectral width of vortex array laser is up to 16.8 nm, and 51 longitudinal modes oscillate. Inversion population is extremely important for stability of singularity-controllable Raman laser by transverse-mode locking, the experimental result is consistent with theory in transverse laser and interference pattern. This work of achieving vortex-array with transverse-mode locking creatively provides a compact Raman laser source, which endows more flexibilities in vortex laser applications.

Nanosecond high-peak-power vortex-pulsed lasers show application in material processing, high-capacity optical communication, and quantum information processing. This study generated nanosecond, high-peak-power LG 0,1 vortex beams in a Yb:YAG/Cr 4+ :YAG passively Q-switched microchip laser (PQSML) pumped with an annular beam. An annular pump beam, irradiated at 940 nm, was shaped by aligning the uneven distribution of light emitters in a laser diode bar and emitting light from a multimode fiber. An optical coupling system was constructed using two spherical lenses (f = 8 mm). The diameter was 80 μm at the focus spot. A linear increase in the average output power was achieved with a slope efficiency of 12.4%. The average output power of the vortex laser was 256 mW at an incident pump power (P in ) of 5.7 W. Vortices oscillated in a single-longitudinal mode when P in < 4.2 W, and the laser attained a pulse width of 2 ns and peak power of 28 kW. Conversely, when A P in > 4.2 W, vortices oscillated in a multi-longitudinal mode, and the laser attained a peak power of approximately 19 kW and pulse width of less than 2.2 ns. The vortex laser with a pulse energy of 42 μJ operated at a repetition rate of 6.3 kHz. A high-beam-quality and high-purity vortex-pulsed laser generated in the compact PQSML shows potential applications in integrated photonics, such as quantum communication and optical trapping.

Actively Q-switched (AQS) fiber laser and solid-state laser (SSL) are widely used for photoacoustic microscopy (PAM). In contrast, passively Q-switched (PQS) SSL not only maintains most of the merits of AQS lasers, but also exhibits unique advantages, including the pulse width (PW), pulse repetition rate (PRR) tunability, wavelength, compactness, and cost. These advantages all benefit the PAM. However, there are few reports demonstrating the performance of PQS-SSL on PA imaging. Here, we demonstrate a compact PQS-SSL for fast and efficient PA imaging. The laser uniquely maintains a constant PW (~2 ns) and pulse energy (~3 μJ) during the PRR variation (30-100 kHz), which is valuable for preserving a stabilized imaging performance at different scanning rates. The PA imaging performance is compared by a resolution target and showcased by whole-body scanning of an embryonic zebrafish in vivo. The performance indicates that PQS-SSL is a promising candidate for PAM.

The optical in-phase and quadrature modulator (IQM) is typically utilized as an optical single-sideband (SSB) transmitter for its simple structure and low cost. It requires the modulator biases to be slightly offset for generating the optical carrier. However, this poses significant challenges in the bias control circuits, as most off-the-shelf automatic bias control (ABC) modules are designed to stabilize the IQM at its carrier suppression point for coherent optical communication. In this paper, a novel arbitrary ABC scheme is proposed to stabilize the carrier-to-signal power ratio (CSPR) of an optical SSB signal over long-term operation. This scheme uses SSB rather than double-sideband (DSB) sinusoidal signals as the dither signals. It does not violate the minimum phase condition, thus avoiding performance penalties compared to the conventional ABC scheme in which the DSB dither signal is used. We also develop a closed-form expression to reveal the relationship between the control parameter in the ABC algorithm and the CSPR of the optical SSB signal. By this means, the optical SSB transmitter can automatically adjust its bias voltages and stabilize them at a given CSPR value. The experimental results with ∼80 Gb/s optical SSB signal show that our proposed ABC scheme is effective in stabilizing the bias of the IQM at any point and maintains the CSPR value of the optical SSB signal over hours. It is also shown that the proposed method leads to 1 dB improvement in the receiver sensitivity compared with the traditional ABC technique.

Lasers have been widely used for pest control because they are efficient and effective to kill pests. Efficient pest control has been achieved with pulsed lasers, however, there is less investigation of effects of pulse characteristics on the pest mortality. Here, the effects of laser beam diameter, pulse width, peak power, and repetition rate of a compact passively Q-switched microchip laser on the mortality rate of Drosophila melanogaster have been studied. The lethality dosing for 90% mortality rate (LD90) Drosophila melanogaster has been utilized for evaluating the effects of passively Q-switched laser on mortality of insects. The beam diameter comparable to the size of Drosophila melanogaster is effective and economic for killing insects. The energy fluence required for LD90 decreases about 6.5% as pulse width is shortened from 1.5 ns to 850 ps. The energy fluence required for LD90 decreases about one-third as the peak power of passively Q-switched microchip laser increases four times from 6.94 kW to 27.48 kW. The energy fluence required for LD90 decreases dramatically from 16.02 J/cm2 to 12.77 J/cm2 as repetition rate increases from 5.05 kHz to 9.9 kHz and then tends to keep as a constant around 12.7 kHz with further increase of repetition rate. Nanosecond passively Q-switched microchip laser with high peak power and high repetition rate is a promising light source for effective and efficient pest control.

Functional photoacoustic microscopy (PAM) requires laser sources with multiple wavelengths targeting abundant substances, where lipid and water are important components of living organisms. Here, we propose to use a single compact dual-wavelength passively Q-switched solid-state laser as the excitation source to directly achieve PA differentiation of water and lipid simultaneously. The main contribution of our work is to use the excitation difference under 1064- and 1176-nm lasers for mapping water and lipid in PAM, respectively. Meanwhile, the miniature structure (cavity size: ∼10 × 10 × 5.5 mm3) of the laser source is not only promising for portable applications but also benefits the PA-desired nanosecond (<2 ns) laser pulse establishment. Our technique is confirmed by efficient PA imaging of water and lipid in biological tissues at high spatial resolution and improved sensitivity. This laser provides a novel and low-cost imaging source for PAM to track changes in water and lipid distribution.