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A 253 J with 26 ns at 0.2 Hz laser performance was demonstrated using a LD pumped cryogenically cooled Yb:YAG ceramics laser amplifier. A high energy storage of 344 J was achieved with a stored energy density of 0.58 J/cm3 using a 1 kJ output multidirectional-pumping system. High energy-extraction efficiency of 56.5% was achieved with high energy fluence of 4.63 J /cm2. To the best of our knowledge, this is the highest output energy obtained with a repetitive nanosecond pulse by LD pumped solid-state laser. This paper presented a design of 1 kJ amplifier based on experimentally proven numerical data.

Thrombolytic therapy in the treatment of cardiogenic acute cerebral embolism caused by coagulated blood carries the risk of hemorrhagic complications, and there is a need to develop safer and more reliable treatment methods. Laser thrombolysis therapy, which utilizes the difference in energy absorption between the thrombus and the arterial wall, has shown promise as a new treatment method because it can selectively act only on the thrombus. It has not been applied clinically, however, and one of the main reasons for this is that its underlying mechanism has not been elucidated. We developed a pulse laser thrombolysis system for treating cerebral blood vessels that consists of a diode-pumped solid-state neodymium-yttrium aluminum garnet laser, which has excellent stability and maintainability and is suitable for clinical applications coupled to a small-diameter optical fiber. Moreover, we analyzed the mechanisms that occur during pulsed laser irradiation of transparent glass tubes and gelatin phantoms. We found that bubbles form as a thermal effect in addition to ablation of the pulsed laser irradiation. Furthermore, we detected no shock waves or water jets associated with the bubbles. We analyzed the bubbles’ dynamics and growth rate, and their effect on a rabbit blood clot phantom. We concluded that the bubbles generated by the laser irradiation physically cut the thrombus and thereby had a thrombectomy effect. We believe that this study will clarify the mechanism of laser thrombolysis therapy and contribute greatly to the realization of its clinical application.

A 11.5 J at 40 ns output has been obtained from a diode-pumped cryo-cooled Yb:YAG ceramics active-mirror laser amplifier system. The system consists of two amplifier heads which has four Yb:YAG ceramic disks and two pump LD modules. The Yb:YAG ceramics are cooled by conventional cryostat from rear side and are pumped by LD modules from front-side. A pump pulse is delivered to Yb:YAG ceramics coaxially with a seed pulse to reduce damage risk at a dielectric coating of Yb:YAG ceramics due to simplified coating design. To realize this system design, a LD module has been developed to keep a rectangle pattern with side length of around 37 mm among imaging depth of about 10cm at working distance of about 410 mm. As an experimental result of two pass amplification, a 11.5 J pulse energy was obtained with input energy of 1.0 J and total pump energy of 90.2 J. Then, an optical-to-optical conversion efficiency was 11.6% and an extraction efficiency was estimated to be 42%. In our knowledge, this is the highest output energy with nano second pulse duration in cryo-cooled Yb:YAG active-mirror laser amplification scheme. A repetition rate of 0.05 Hz depends on a limitation of a repetition rate of the seed pulse. A dependence of small-signal-gain on pumping repetition rate of the active-mirror laser head was experimentally evaluated. From the experimental result, we have estimated a feasible repetition rate of over 5 Hz. A 10 Hz operation will be demonstrated to reduce a thermal resistance between Yb:YAG ceramics and cryostat. Finally, this laser amplifier system is installed to a 100-J class laser system as preamplifier.

A 100 J class diode-pumped solid-state laser system has been developed as a platform for acceleration of laser processing application. A 117 J output of pulse energy has been demonstrated with the main amplifier.

We demonstrated 117-J laser output in a nanosecond regime with a diode-pumped Yb:YAG ceramic laser amplifier. The repetition rate was 0.05 Hz, and the pulse duration was around 40 ns. 5-J input energy was amplified by two cryogenically cooled Yb:YAG ceramic laser heads. Six Yb:YAG ceramic disks in each laser head were cooled by cryogenic helium gas with a temperature of 175 K. The output energy of the first and second laser heads was about 28 and 117 J.

A 64J at 10 ns output was demonstrated by diode-pumped cryogenically cooled Yb:YAG ceramic laser amplifier. An extraction efficiency was evaluated 43.3% at stored energy of 148J with small-signal-gain of 20.4.

A compact 40kW at 10Hz output LD module has been developed for cryogenically cooled Yb:YAG ceramics active-mirror laser amplifiers for 10J at 10Hz output laser system. Pumping intensity is 2.5kW/cm2 and footprint of the LD module is 18cm × 77cm.

The authors have demonstrated an optical parametric chirped-pulse amplification (OPCPA)/Yb:YAG ceramic thin disk hybrid laser system having hundred mJ level pulse energy sub-picosecond pulse duration with high temporal contrast. At an input chirped-pulse energy of 3.8 mJ from an OPCPA preamplifier an output energy of 130 mJ has been generated from multipass diode-pumped Yb:YAG ceramic thin disk amplifier. A recompressed pulse duration of 450 fs with a contrast level of less than 7.2×10−9 at −150 ps before the main pulse has been obtained. The contrast level is the highest value achieved in Yb:YAG chirped-pulse amplification (CPA) laser system at 100 mJ level.

We report the highest energy broadband laser pulses at a center wavelength of 1030 nm based on optical parametric chirped-pulse amplification (OPCPA). We have demonstrated amplification of 1030 nm femtosecond laser pulses from a broadband Yb oscillator to over 6.5 mJ with a total gain of greater than 107 achieved in a single pass through only 56 mm of gain material at a 10 Hz repetition rate. The amplified spectral bandwidth of 10.8 nm affords recompression to a 230 fs pulse duration following amplification. As an alternative to the regenerative amplifier (RA) this system is one of the more promising candidates for realizing compact, high intensity, direct diode-pumped, high repetition rate femtosecond Yb:YAG chirped-pulse amplification (CPA) in laser systems.

Double-clade crystalline fiber waveguide (CFW) has been produced by using adhesive-free bond (AFB®) technology. The waveguide consists of a 1 at.% Yb:YAG core, un-doped YAG inner cladding and ceramic spinel outer cladding. It is a direct analog of the conventional double-clad glass fiber laser in the crystal domain. Signal gain of 45 or 16.5 dB has been measured in a preliminary master oscillator power amplifier (MOPA) experiment. Due to the high laser gain and the weak Fresnel reflection at the uncoated waveguide ends, the CFW even starts self-lasing above a certain pump power. Laser output power of 4 W in the backward propagation direction has been measured for input pump power of 44 W. After considering the same amount of forward propagated laser power, the laser efficiency to the absorbed pump power is estimated to be about 44%. In principle, CFW can have extremely large single mode area for high efficiency and high power laser applications. So far, Single mode area < 6700 μm2 has been demonstrated in Er:YAG CFWs.

We have developed high average power MOPA laser system with SHG unit on the table top size (3 × 1.5m). At the wavelength 1064nm has been obtained the max average output power of 715W. We have achieved the average power 180W at the wavelength 532nm, the pulse width of about 100ns, the frequency of 1kHz. And the power efficiency of the SHG from the wavelength of 1064nm to 532nm was obtained about 25.6%.

We have developed high average power MOPA with output power of 174W at the pulse width of about 100ns, the frequency of 1kHz, and the wavelength of 532nm.

We are developing a high-repetition and high-average-power Nd:YAG laser amplifier pumped by fiber coupled LDs in order to apply to laser machining of carbon composite materials such as CFRP (Carbon Fiber Reinforced Plastic). Final target is 1.5 kW output at wavelength of 1064 nm by 8 kW LD pumping. The amplifier consists of several Nd:YAG ceramic thin discs on a non-doped ceramic YAG block. At first, we measured wave-front distortion and small-signal gain of a prototype amplifier whose target is more than 500 W output.

We have demonstrated an optical parametric chirped pulse amplification (OPCPA)/Yb:YAG ceramic thin disk hybrid laser system having hundred mJ level pulse energy sub-picosecond pulse duration with high temporal contrast. At an input chirped-pulse energy of 3.8 mJ from an OPCPA preamplifer an output energy of 130 mJ has been generated from multipass laser diode-pumped Yb:YAG ceramic thin disk amplifier. A recompressed pulse duration of 450 fs with a contrast level of less than 7.2×10−9 at −150 ps before the main pulse has been obtained. The contrast level is the highest value achieved in Yb:YAG chirped pulse amplification (CPA) laser system with hundred mJ level.

Yb:YAG CPA have a potential to develop a compact, high peak power at high repetition rates. For high energy pulses of short duration Yb:YAG regenerative amplifiers have mainly been studied for which significant prepulse and amplified spontaneous emission (ASE). In laser proton acceleration studies it is very important to suppress the prepulse and ASE levels, because a preplasma is generated before the peak of the laser pulse, therefore the maximum proton energy is limited. To overcome this problem, the OPCPA can efficiently provide high gain for the main pulse while suppressing prepulse amplification. Here we have first demonstrated a hundred mJ level, femtosecond of an OPCPA/Yb:YAG hybrid laser system with a contrast level of 10−9 at −150 ps.

The broad absorption bandwidth of ytterbium (Yb) is well-suited to laser diode pumping at 940 nm. Because Yb is known for its low quantum defect, thermal loading is significantly reduced. Consequently, Yb doped crystals, especially Yb:YAG, show promise for developing compact, high peak power laser systems at high repetition rates. For high energy pulses of short duration Yb:YAG regenerative amplifiers have mainly been studied where the generation of significant prepulse and amplified spontaneous emission (ASE) is known. At higher intensities (for example ∼ 1018Wcm−2 and beyond) laser-matter interactions can require suppression of prepulse and ASE intensity in order to maintain or control the target state that a short or ultrashort main pulse would irradiate. In many cases it is therefore critical to avoid significant preplasma formation. To solve these problem, the optical parametric chirped pulse amplification (OPCPA) can efficiently provide high gain of the main pulse while suppressing prepulse amplification and reducing gain narrowing of the spectrum. We present in this conference the first Yb femtosecond oscillator based OPCPA demonstration at 1030 nm and with spectral bandwidth adequate for amplifying femtosecond pulses. Direct laser diode (LD) amplification of 1030 nm light makes this OPCPA a feasible preamplifier for a compact, high contrast, energetic, short pulse laser systems that can be considered for development of laser-driven proton accelerators.

A compact green-light source with 5.1 W at 531 nm and 0.31 overall optical-to-optical efficiency, based on an intracavity frequency-doubled Nd:GdVO4 micro-laser that is pumped by diode laser directly into the emitting level, is described.

A continuous-wave diode end-pumped Nd:GdVO4 laser intracavity frequency-doubled by LBO nonlinear crystal with 5.3 W green output power, 66% conversion of the available infrared power and 31% overall optical-to-optical conversion efficiency is reported.