Fiber-coupled Laser Diode Research Articles

CW and AO Q-switched operation of a dual-crystal Tm, Ho:GdVO4 laser pumped by two diodes

Continuous wave (CW) mode and acousto-optic (AO) Q-switched mode operation of a dual-crystal Tm, Ho:GdVO4 laser is reported. The dual-crystal Tm, Ho:GdVO4 laser with output wavelength of 2.05 μm was pumped by two laser diodes (LDs). The Tm, Ho:GdVO4 crystals were cooled by liquid nitrogen and pumped by two fiber-coupled LDs with a center output wavelength of 801.0 nm. A 20.5 W output power was obtained at a 255 mm physical cavity length in CW mode operation, and a 19.6 W average power was obtained at a pulse repetition frequency (PRF) of 10 kHz with a 19 ns pulse duration. Also, the efficiency loss of the laser is not more than 4.4% from CW mode to Q-switch mode, and the M2 factor, which is measured by the traveling knife-edge method, does not exceed 1.2.

Lasers for Nanometrology

AbstractOver the last few decades the interest in phenomena on nanoscale or even atomic scale has increased significantly.A prominent, but at the same time very demanding technique is atomic force microscopy (AFM). AFM can reveal surface topographies at atomic resolution or be used to measure small forces in the range of only a few piconewtons. This exacting technique requires highly stable laser sources with specific features, including low power noise and the possibility to oppress unwanted interference.The 51nano series of lasers was specially developed to provide these indispensable features of low noise, reduced coherence and low speckle contrast in order to achieve the demanding stability standards required in nanotechnology and atomic force measurements. Particle measurements and alignment tasks are other possible applications for these stabilized, fiber‐coupled laser diode beam sources.

Three-dimensional velocity near-wall measurements by digital in-line holography: calibration and results

Velocity measurements in the vicinity of an obstacle remain very complicated even when optical diagnostics based on displacement of micrometric tracers are considered. In the present paper, digital in-line holography with a divergent beam is proposed to measure the three-dimensional (3D) velocity vector fields in a turbulent boundary layer and, in particular, on the near wall region of a wind tunnel. The seeding droplets (1-5 μm) transported by a turbulent airflow are illuminated by a couple of laser pulses coming from a fiber coupled laser diode. These double exposure holograms are then recorded through a transparent glass reticle specially designed for this application with an accurate surface positioning combined with a particularly attractive in situ calibration method of the investigation volume (less than 10 mm(3)). The method used for processing holograms recorded in such a configuration is detailed. Our original calibration procedure and the assessment of its accuracy are presented. Our holographic probe has been tested in a wind tunnel for a large range of different velocities. Then 3D velocity vector fields extracted from more than 13000 holograms are analyzed. Statistical results show the capability of our approach to access in a turbulent boundary layer. In particular, it leads to relevant measurements for fluid mechanics such as velocity fluctuation and the shear stress in the very close vicinity of a wall.

Efficient Q-switched Tm:YAG ceramic slab laser pumped by a 792 nm fiber laser

High-efficient continuous wave (cw) and actively Q-switched Tm:YAG ceramic lasers were described successfully. Pumping with fiber coupled laser diode at 792nm, the maximum cw output power of 5.21W with improved beam quality was obtained with a slope efficiency of 46.1%. The shortest pulse width of 107ns was achieved with the pulse repetition frequency (PRF) of 0.5kHz, resulting in a largest pulse energy of 1.44mJ and a highest peak power of 13.42kW.

High-energy directly diode-pumped Q-switched 1617 nm Er:YAG laser at room temperature

We describe high-energy Erbium-doped yttrium aluminum garnet (Er:YAG) lasers operating at 1617 nm, resonantly pumped using 1532 nm fiber-coupled laser diodes. A maximum continuous wave output power of 4.3 W at 1617 nm was achieved with an output coupler of 20% transmission under incident pump power of 29.7 W, resulting in an optical conversion of 14% with respect to the incident pump power. In Q-switched operation, the pulse energy of 11.8 mJ at 100 Hz pulse repetition frequency and 81 ns pulse duration was obtained. This energy is the highest pulse energy reported for a directly diode-pumped Q-switched Er:YAG laser operating at 1617 nm.

Energy efficiency of drilling granite and travertine with a CO2 laser and 980 nm diode laser

Using lasers to drill hard rock presents potential advantages compared to conventional mechanical drilling, such as higher penetration rates and reduced vibration. Before realistic drilling tools can be proposed, the influence of important parameters and the mechanisms involved in drilling different rocks with different lasers must be understood. In this work, we investigate the efficiency of laser drilling of granite and travertine with a CO2 laser and a 980 nm fiber coupled diode laser. At the drilling surface, the maximum CW power delivered by the CO2 laser was 140 W, while the diode laser delivered up to 215 W. Even at these modest power levels, it was possible to drill holes with diameters of the order of 8 mm at efficiencies varying from 40 kJ/cm3 to 150 kJ/cm3. The optimum laser exposure period of time was also investigated. Finally, x-ray diffraction and fluorescence analysis, as well as Tg (Thermogravimetry) and DTA (Differential Thermal Analysis) measurements, were performed on the rocks samples used.

A passively mode-locked Nd:YVO4 laser with a carbon nanotube saturable absorber

We report the mode locking of a diode pumped Nd:YVO4 crystal laser by using a transmission-type single-walled carbon nanotube saturable absorber. The laser operated at 1064 nm pumped by a fiber coupled laser diode with the cavity length of 1826 mm, generated a pulse width of 14 ps at a repetition rate of 82 MHz. The output power of 120 mW was obtained at the absorbed pumping power of 1400 mW.

A high power CW Ho,Tm:GdVO4 laser

In this paper, we report a 22.7 W continuous wave (CW) diode-pumped cryogenic Ho( at %), Tm(3 at %):GdVO4 laser. The pumping sources of Ho,Tm:GdVO4 laser are two fiber-coupled laser diodes with fiber core diameter of 0.4 mm, both of them can supply 42 W power laser operating near 802 nm. For input pump power of 64.7 W at 802.5 nm, the output power of 22.7 W in CW operation, optical-to-optical conversion efficiency of 35.1% at 2.05 μm has been attained. The M2 factor was found to be 2.0 under an output power of 16.5 W.

A Dual-Crystal Cavity Ho,Tm:GdVO4 Laser

We report a 31.2 W cw diode-pumped cryogenic Ho(0.4at.%),Tm(4at.%):GdVO4 laser in a dual-crystal cavity. The pumping sources are two fiber-coupled laser diodes with a fiber core diameter of 0.4 mm, both of which can supply 42 W near 802 nm. With an incident pump power of 70.3 W at 802.4 nm, a cw output power of 31.2 W at 2.05 μm is attained, corresponding to an optical-to-optical conversion efficiency of 44.4%. The M2 factor is measured as ∼1.3 under an output power of 20 W.

Compact, efficient diode-end-pumped Nd:GdVO4 slab continuous-wave 912-nm laser

A fiber-coupled laser-diode (LD) end-pumped Nd:GdVO4 slab continuous-wave (CW) 912-nm laser and an LD bar end-pumped Nd:GdVO4 slab CW 912-nm laser are both demonstrated in this paper. Using the fiber-coupled LD of end-pumped type, a highest CW 912-nm laser output power of 10.17 W is obtained with a high optical-to-optical conversion efficiency of 24.6% and a slope efficiency of 34.5%. The measured M2 factors of beam quality in x and y directions are 5.3 and 5.1, respectively. Besides, an LD bar of end-pumped type is used to realize CW 912-nm laser output, which has the advantages of compactness and low cost. When the pump power is 38.8 W, the output power is 8.87 W and the measured M2 factors of beam quality in x and y directions are 16 and 1.31, respectively. In order to improve the beam quality of the 912-nm laser at x direction, a new quasi-concentric laser resonator will be designed, and an LD bar end-pumped Nd:GdVO4 slab high-power CW 912-nm TEM00 laser will be realized in the future.

A Case of Squamous Cell Carcinoma Treated with Chlorine Photodynamic Therapy

.A 79-year-old woman presented with a 2-year history of recurrent ulcerated lesion on the scalp vertex. There was no history of skin disease or trauma on the affected area. Clinical examination revealed a walnut-sized central crusted ulcer surrounded by erythematous, elevated indurative border (Fig. 1A). The histological features showed invasion of the dermis by irregular masses of epidermal cells that were predominantly mature squamous cells showing relatively slight atypicality. The depth of microscopic invasion was 3 mm. There was no presence of perivascular or perineural invasions (Fig. 2). A diagnosis of well-differentiated SCC was made on the basis of these clinical and histological findings. Because of her age and refusal of surgery, we decided to treat her with chlorine PDT. At first, we considered topical PDT with chlorine. But as the optimal topical agent could not penetrate to the needed full depth, we planned instead systemic chlorine PDT. Pretreatment evaluation included a history and physical examination, routine laboratory evaluation and photographic documentation. She has no photosensitivity and there were no signs to imply any other systemic diseases including internal malignancy. No further systemic workup was performed as is usual with cutaneous SCC. The patient was admitted to the hospital and the photosensitizer Radachlorin Ⓡ (RADA-PHARMA, Moscow, Russia) was injected intravenously for 30 minutes at a dose 0.9 mg/kg. Laser irradiation was carried out for 2 hours after the injection. As a light source we used a fiber coupled diode laser ‘LAHTA-MILON

百瓦级高亮度光纤耦合半导体激光模块的研制

Three 976 nm diode laser short bars were used as submodule to manufacture high brightness fiber coupled module with CW hundred watts class output power.First,beam transform systems were employed to shape beams emitted from each submodlue;Second,the three beams were stacked in direction of lower beam parameter product by means of spatial multiplexing technology;Finally,the laser was focused into a multimode fiber with 200 μm core diameter and NA=0.22 by optimized lens.Experiment result showed that divergence angle of the focused laser beam was 24.8° and its beam waist diameter was 175.2 μm;laser output from fiber could reach to 107 W,equalizing brightness of 2.23 MW/(cm2·sr),which is a higher level in China.Furthermore,the wall plug efficiency is 43.1% when driving current is 52.5 A,which is far higher than that of solid state laser.Finally the thermal resistance was computed by means of measuring spectrum with different current and the result is 1.29 K/W which indicates favorable heat dissipation of the module.All of the result showed that the module can be used in the field of pumping fiber lasers,medical,material processing and so on.

Laser spectrum of a high power Tm, Ho:GdVO4 laser

In this paper, we report a 18.8 W continuous wave and 18.4 W Q-switched diode-pumped cryogenic Tm(5 at %), Ho(0.5 at %):GdVO4 laser. The pumping source of Tm, Ho:GdVO4 laser is a fiber-coupled laser diode with fiber core diameter of 0.4 mm, supplying 42 W power at 802.5 nm. For input pump power of 41.9 W at 802.4 nm, the output power of 18.8 W in CW operation, optical-to-optical conversion efficiency of 45% at 2.05 μm and the average output power of 18.4 W in Q-switched operation, optical-to-optical conversion efficiency of 44% at 2.04 and 2.05 μm have been attained. The emission wavelengths of the Tm(5 at %), Ho(0.5 at %):GdVO4 laser were firstly compared when it worked in CW mode and Q-switched mode.

Continuous-wave and actively Q-switched Nd:LSO crystal lasers

With a fiber coupled laser diode array as the pump source, Nd-doped Lu2SiO5 (Nd:LSO) crystal lasers at 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions were demonstrated. The active Q-switched dual-wavelength lasers at about 1.08 μm, as well as continuous-wave (CW) and active Q-switched lasers at 1357 nm are reported for the first time, to the best of our knowledge. Considering the small emission cross-sections and long fluorescence lifetime, this material possesses large energy storage ability and excellent Q-switched properties. The special emission wavelength at 1357 nm will have promising applications to be used in many fields, such as THz generation, pumping of Cr3+:LiSAF, repumping of strontium optical clock, laser Doppler velocimeter and distributed fiber sensor.

Diode both ends pumped two crystals Tm:YLF laser

In this paper, we report two crystals Tm:YLF laser pumped by a fiber coupled diode laser with total power of 180 W at 792 nm. When the incident power reached up to 117.0 and 37.3 W of the emission wave-length at 1.91 μm was achieved. Through linear fit, the corresponding slope efficiency of 38.5%, optical-to-optical conversion efficiency of 31.9% and the beam quality factor of M 2 ∼ 1.1 were obtained, indicating nearly diffraction limited beam propagation. To our best knowledge, this is the best beam quality among the reported paper results under the similar experiments.

Diode pumped operation of 1 mm Tm,Ho:YAP microchip laser

A single-longitudinal-mode (SLM) operation of a c-cut 1 mm Tm(5%), Ho(0.3%):YAP micro-chip laser pumped by a fiber-coupled diode-laser was reported. Under cryogenic temperature, the output power of 216 mW was obtained under the incident power of 2230 mW, corresponding to the slope efficiency was 13.6%. As much as 133 mW output and slope efficiency of 4.9% was obtained under the pump power of 3000 mW at 291 K. In addition, a maximum SLM output power of 30 mW at wavelength of 2130.56 nm is demonstrated under 77 K.

Polarization manipulated solid-state lasers with crystalline-orientations

The polarization states of 〈111〉-cut Yb:YAG crystal microchip lasers were investigated by pumped with the elliptically polarized pump beam from fiber-coupled laser-diode. The manipulated polarized lasers were achieved in laser-diode pumped Yb:YAG microchip laser by controlling the crystalline-orientations in 〈111〉-growth Yb:YAG crystal. Generally elliptically polarized lasers were obtained in laser-diode pumped Yb:YAG microchip lasers. However, crystalline-orientation manipulated linearly polarized laser was obtained when six different sites with different crystalline orientations were set to parallel to the major axis direction of the elliptically polarized pump beam. Six different sites in Yb:YAG crystal were separated with 30° and 90°, which were responsible for the linearly polarized laser oscillations. Circularly polarized lasers were observed when a Yb:YAG crystal was aligned to a special position between two sites responsible for linearly polarized laser oscillation. Effects of the polarization states of pump source on the laser polarization states of Yb:YAG microchip lasers and polarization direction of different polarized lasers with respect to Yb:YAG crystal rotation was addressed.

Size measurement of bubbles in a cavitation tunnel by digital in-line holography

Digital in-line holography (DIH) with a divergent beam is used to measure size and concentration of cavitation bubbles (6-100 μm) in hydrodynamic facilities. A sampling probe is directly inserted in the cavitation tunnel, and the holograms of the bubbles are recorded through a transparent test section specially designed for DIH measurements. The recording beam coming from a fiber-coupled laser diode illuminates the sample volume, and holograms are recorded by a CMOS camera. From each hologram, the sampling volume can be reconstructed slice by slice by applying a wavelet-based reconstruction method. Because of the geometry of the recording beam, a magnification ratio must be introduced for recovering the 3D location and size of each bubble. The method used for processing holograms recorded in such a configuration is presented. Then, statistical results obtained from 5000 holograms recorded under different pressures in the cavitation tunnel are compared and discussed.

885 nm pumped, high efficiency single-frequency Nd:YAG ring laser

We report an efficient single-frequency ring laser pumped directly into emitting level by a fiber-coupled laser diode (FCLD) at 885 nm for the first time. 4.8 W laser at 1064 nm was obtained in a 0.7 at % Nd:YAG with 63% slope efficiency and 51.7% light-light efficiency in absorbed pump power. At the same time, the line width of the longitudinal mode was about 50 MHz, and the beam was nearly diffraction-limited with M2 ≈ 1.07.

Efficient High Power Ho,Tm:GdVO4 Laser

We report a 22.3 W cw diode-pumped cryogenic Ho(0.5at.%),Tm(at.5%):GdVO4 laser at a wavelength of 2.05 μm. It is pumped by two fiber-coupled laser diodes with a fiber core diameter of 0.4 mm, both of which provide 42 W pump power near 802 nm. A cw output power of 22.3 W was obtained at the pump power of 51.0 W, corresponding to an optical-to-optical conversion efficiency of 43.7% when the ratio of the pump beam to oscillating laser beam in the crystal was ∼1.33:1. The M2 factor was found to be 2.0 under an output power of 16.5 W.