基于准分子激光微加工的光热微驱动器(英文)

提出了基于光热(PT)微膨胀原理的新型光热微驱动技术.设计了一种能将纵向光热膨胀转化成横向偏转的微驱动器.以AutoCAD设计图为基础,采用KrF准分子激光微加工系统,在单层高密度聚乙烯(HDPE)上加工出长1 500μm、宽250μm、厚40μm的开关式光热微驱动器.从微驱动器的扫描电子显微镜(SEM)图可以看出,微驱动器形状与AutoCAD设计值符合良好.光热微驱动实验采用脉冲频率可调的半导体激光器(4 mW,650 nm)作为驱动源.实验结果表明,在一定的脉冲频率范围(如0～17 Hz)内,光热微驱动器具有良好的静态和动态特性,其横向偏转量最大可达11μm,足以实现微开关功能.这种光热微驱动器可由激光束直接控制,具有原理新颖、结构简洁、体积小、易于加工制作等特点,在微纳米技术领域和微光机电系统(MOEMS)中具有广阔的应用前景.     

Measurement of the Optical Force and Trapping Range of a Single-beam Gradient Optical Trap for Micron-sized Latex Spheres

Abstract

A single-beam gradient optical trap was constructed using a 20 mW 632·8 nm He–Ne laser coupled to an optical microscope. Latex spheres were trapped in water at the focal point of a tightly-focused laser beam, which was generated using a 100 × objective. The efficiency of the trap was evaluated by determining the maximum speeds at which the trapped particles could be manipulated. Typical maximum speeds of tens of microns per second were recorded, at the maximum trapping power of 6·7 mW. The effective transverse trapping range for 1–7 μm diameter latex spheres was measured to be 1–3 μm, and the maximum transverse optical force on 1–12 μm diameter latex spheres varied in the range 0·4–4·5 pN.     

High-efficiency continuously tunable single-frequency doubly resonant optical parametric oscillator

We report a high-efficiency continuously tunable single-frequency doubly resonant optical parametric oscillator (OPO) based on periodically poled KTiOPO4. Pumped by a frequency-doubled Nd:YLF laser at 526.5 nm, the OPO has a low threshold of 30 mW and can deliver up to 156 mW single-frequency output at 0.8 μm and 89 mW single-frequency output at 1.5 μm with 390 mW of pump power. Coarse and continuous frequency tuning are also demonstrated experimentally.     

All-fiber Q-switched operation of thulium-doped silica fiber laser by piezoelectric microbending

We demonstrate an all-fiber Q-switched laser operation in the 2 μm region on the basis of a dynamic periodic microbend and pulsed-pump configuration. A single-mode thulium-doped silica fiber is pumped by 1.6 μm-band laser diodes, and the dynamic loss is introduced in the fiber ring resonator by the periodic microbend that is electrically controlled with a piezoelectric actuator. When the voltage-off period of the piezoelectric actuator is set at 20 μs for the pump power of 120 mW, the output pulse power is measured by 420 mW with a pulse width of 1.3 μs.     

High-power single-mode laser diodes (λ = 1.1–1.2 μm) based on quantum-confined AlInGaAs/InP heterostructures

Quantum-confined AlInGaAs/InP laser heterostructures emitting at a wavelength of 1.18 μm have been grown by metalorganic vapor-phase epitaxy. An output radiation power of 40 mW in a single-mode CW regime has been obtained using a diode based in this structure with a mesastrip width of W = 4 μm. The total maximum CW emission power amounted to 75 mW.     

Sensitivity of the thermocapillary method of thickness determination for transparent liquid films on horizontal absorbing substrates

We present data on the sensitivity of a new method of determining the thicknesses of thin films on flat horizontal substrates, based on the measurement of a stationary thermocapillary response. In the range of film thicknesses exceeding the thermocapillary rupture thickness by no more than 10 μm, the error of the film thickness determination is no greater than 1–2 μm. By increasing the power of the laser beam inducing the thermocapillary convection from 3.5 to 16.5 mW, it is possible to keep the relative error of measurement within 5% in the range of film thicknesses from 150 to 1000 μm for liquids with viscosities within 0.8–5.6 cSt.     

Photothermal nanoblade for large cargo delivery into mammalian cells

It is difficult to achieve controlled cutting of elastic, mechanically fragile, and rapidly resealing mammalian cell membranes. Here, we report a photothermal nanoblade that utilizes a metallic nanostructure to harvest short laser pulse energy and convert it into a highly localized explosive vapor bubble, which rapidly punctures a lightly contacting cell membrane via high-speed fluidic flows and induced transient shear stress. The cavitation bubble pattern is controlled by the metallic structure configuration and laser pulse duration and energy. Integration of the metallic nanostructure with a micropipet, the nanoblade generates a micrometer-sized membrane access port for delivering highly concentrated cargo (5 × 10(8) live bacteria/mL) with high efficiency (46%) and cell viability (>90%) into mammalian cells. Additional biologic and inanimate cargo over 3-orders of magnitude in size including DNA, RNA, 200 nm polystyrene beads, to 2 μm bacteria have also been delivered into multiple mammalian cell types. Overall, the photothermal nanoblade is a new approach for delivering difficult cargo into mammalian cells.     

Damage threshold determination of bulk polymer samples using pulsed photothermal deflection technique

Photothermal deflection technique was used for determining the laser damage threshold of polymer samples of teflon (PTFE) and nylon. The experiment was conducted using a Q-switched Nd-YAG laser operating at its fundamental wavelength (1-06μm, pulse width 10 nS FWHM) as irradiation source and a He-Ne laser as the probe beam, along with a position sensitive detector. The damage threshold values determined by photothermal deflection method were in good agreement with those determined by other methods.     

Laser heating of uncoated optics in a convective medium

Powerful, long-pulse lasers have a variety of applications. In many applications, optical elements are employed to direct, focus, or collimate the beam. Typically the optic is suspended in a gaseous environment (e.g., air) and can cool by convection. The variation of the optic temperature with time is obtained by combining the effects of laser heating, thermal conduction, and convective loss. Characteristics of the solutions in terms of the properties of the optic material, laser beam parameters, and the environment are discussed and compared with measurements at the Naval Research Laboratory, employing kW-class, 1 μm wavelength, continuous wave lasers and optical elements made of fused silica or BK7 glass. The calculated results are in good agreement with the measurements, given the approximations in the analysis and the expected variation in the absorption coefficients of the glasses used in the experiments.     

Intracavity frequency doubling and Q switching in diode-laser-pumped Nd:YVO(4) lasers

A highly efficient and compact Nd:YVO(4) laser is proposed. In cw operation, a single-longitudinal-mode output of 95 mW and a multilongitudinal-mode output of 435 mW have been observed at 1.06 μm with a 1-W diode laser. Using a KTP crystal in the short laser cavity, a green output of 105 mW was generated. A Q-switched pulse with a peak power of 230 W and a pulse width of 8 ns was obtained with the intracavity KTP crystal, which was used as both an electro-optic Q switch and a frequency doubler.     

High-efficiency 1.06-µm output in a monolithic Nd:YVO(4) laser

A miniature 1.5-mm-long monolithic Nd:YVO(4) laser was end pumped with a Ti-sapphire laser. The Nd-doping density was 3 at. %. The maximum output power obtained with 885 mW of absorbed pump power was 495 mW at 1.064 μm. The maximum slope efficiency was 57%, and the output power was only slightly dependent on pump polarization. Laser diode pumping was also demonstrated. Thermal effects were observed to reduce the output power and required active cooling of the laser crystal.     

Determination of the longitudinal profile of a focused Nd:YAG Gaussian beam from second-harmonic generation in a thin KTP crystal

We present an original experiment describing a focused Gaussian laser beam by using second-harmonic generation (SHG) in a thin strip of a nonlinear optical material, in this case KTP doubling of an Nd:YAG laser at 1.064 μm. The dependence of the SHG efficiency on the fundamental beam radius allows the determination of beam parameters by harmonic-power measurements. The characterization of a telescope shows the good precision of this method in radii in the range of 10-100 μm. The average accuracy is 4% for the radius determination and 1.5% for the beam-waist localization.     

Effect of beam waists on performance of the tunable fiber laser based on in-line two-taper Mach-Zehnder interferometer filter

A tunable fiber ring laser based on an in-line two-taper Mach-Zehnder interferometer (MZI) filter was realized, and the effect of beam waists of the tapers on performance of the laser was investigated with different beam waists of 70 μm, 49 μm, and 33 μm. Experimental results show that the tunable laser with MZI length of 1 m and beam waist of 49 μm can cover 16.1 nm with tuning steps of 0.07-0.5 nm, a bandwidth of 10 pm, and a side mode suppression ratio (SMSR) of 40-50 dB. Tuning range is not only determined by the number of the cladding modes but is also affected by the filter loss. Tuning step is determined by the differences of the effective refractive indexes between the cladding modes and the core mode. SMSR is determined by the balance between the extinction ratio of the filter and the cavity loss of the laser due to MZI filter.     

High-power external-cavity AlGaAs/GaAs/InGaAs quantum-dimensional heterolasers (λ = 1.06 μm)

Use of an external cavity with a grating ensures effective narrowing of the linewidth (～0.35 nm) of a high-power multimode semiconductor laser with a broad (100 μm) stripe contact. An output power of up to 550 mW has been reached with experimental external-grating-cavity laser diodes. It is demonstrated that a 3-mm-long multimode laser diode based on a quantum-dimensional AlGaAs/GaAs/InGaAs heterostructure (λ = 1.06 μm) can be used with a directly pumped PPLN crystal waveguide to obtain second-harmonic radiation with λ = 0.532 μm.     

Small-bore hollow waveguides for delivery of 3-µm laser radiation

Flexible hollow glass waveguides with bore diameters as small as 250 μm have been developed for 3-μm laser delivery. All the guides exhibit straight losses between 0.10 and 1.73 dB/m, and the loss increases to between 2.4 and 5.1 dB/m upon bending 1 m of the guides into 15-cm-diameter coils. This behavior is shown to depend strongly on the launch conditions and mode quality of the input beam. The waveguides are capable of efficiently delivering up to 8 W of Er:YAG laser power with proper input coupling, and they are suitable for use in both medical and industrial applications.     

Direct Laser Patterning of Soft Matter: Photothermal Processing of Supported Phospholipid Multilayers with Nanoscale Precision

Direct laser patterning of supported phospholipid multilayers is investigated. Spin coating is used to fabricate stacked bilayers of 1,2‐dioleoyl‐sn‐glycero‐3‐phosphate (DOPA). Photothermal processing with a focused laser beam at λ = 514 nm allows removal of the coating at predefined positions without causing any significant change in adjacent areas. Moreover, processing with nanoscale precision is feasible despite the soft and fluid nature of phospholipid films. In particular, holes with diameters from 1.8 µm down to 300 nm and below are fabricated by using a 1/e² laser spot size of about 2.5 µm. In addition, patterning is also very flexible and can be carried out over macroscopic length scales and at short processing times. Considering these features photothermal laser processing constitutes a powerful tool for micro‐ and nanopatterning of phospholipid films.     

Combination of fiber-guided pulsed erbium and holmium laser radiation for tissue ablation under water

Because of the high absorption of near-infrared laser radiation in biological tissue, erbium lasers and holmium lasers emitting at 3 and 2 μm, respectively, have been proven to have optimal qualities for cutting or welding and coagulating tissue. To combine the advantages of both wavelengths, we realized a multiwavelength laser system by simultaneously guiding erbium and holmium laser radiation by means of a single zirconium fluoride (ZrF(4)) fiber. Laser-induced channel formation in water and poly(acrylamide) gel was investigated by the use of a time-resolved flash-photography setup, while pressure transients were recorded simultaneously with a needle hydrophone. The shapes and depths of vapor channels produced in water and in a submerged gel after single erbium and after combination erbium-holmium radiation delivered by means of a 400-μm ZrF(4) fiber were measured. Transmission measurements were performed to determine the amount of pulse energy available for tissue ablation. The effects of laser wavelength and the delay time between pulses of different wavelengths on the photomechanical and photothermal responses of meniscal tissue were evaluated in vitro by the use of histology. It was observed that the use of a short (200-μs, 100-mJ) holmium laser pulse as a prepulse to generate a vapor bubble through which the ablating erbium laser pulse can be transmitted (delay time, 100 μs) increases the cutting depth in meniscus from 450 to 1120 μm as compared with the depth following a single erbium pulse. The results indicate that a combination of erbium and holmium laser radiation precisely and efficiently cuts tissue under water with 20-50-μm collateral tissue damage.     

Kinoform-only Gaussian-to-rectangle beam shaper for a semiconductor laser

A kinoform that shapes the divergent beam from a semiconductor laser without using any other optical components was designed and fabricated. The kinoform-only concept means that the kinoform must perform both the actual beam shaping as well as focusing the divergent laser beam, correcting for the astigmatism of the laser, and correcting for the spherical aberration of the laser exit window. A rectangular beam of dimensions 1000 μm × 300 μm is formed 42 mm behind the kinoform. Of the total output from the laser, some 50% is incident upon the kinoform, of which ~50% will appear in the rectangular beam. The intensity uniformity error within the rectangle increases from the design value of 8% to 38% because of sensitivity to fabrication errors. The kinoform-only design for beam-shaping applications requires high manufacturing accuracy but is attractive because a system using such a component is easily mounted and aligned and, with the use of kinoform-replication techniques, can be mass produced at low cost.     

Hollow Copper Sulfide Nanoparticle‐Mediated Transdermal Drug Delivery

A photothermal ablation‐enhanced transdermal drug delivery methodology is developed based on hollow copper sulfide nanoparticles (HCuSNPs) with intense photothermal coupling effects. Application of nanosecond‐pulsed near‐infrared laser allows rapid heating of the nanoparticles and instantaneous heat conduction. This provides very short periods of time but extremely high temperatures in local regions, with focused thermal ablation of the stratum corneum. The depth of skin perforations can be controlled by adjusting the laser power. Skin disruption by HCuSNP‐mediated photothermal ablation significantly increases the permeability of human growth hormone. This technique offers compelling opportunities for macromolecular drug and vaccine delivery.