Efficient generation of 200 mJ nanosecond pulses at 100 Hz repetition rate from a cryogenic cooled Yb:YAG MOPA system

A diode-pumped Master Oscillator Power Amplifier (MOPA) laser system based on cryogenic cooled Yb:YAG has been designed, developed and its output performance characterised. The laser system consists of a fibre oscillator, an active mirror regenerative amplifier and a four pass main amplifier. 2.4 mJ, 10 ns, 100 Hz seed pulses from the fibre oscillator/regenerative amplifier arrangement were amplified up to pulse energies of over 200 mJ by using the four pass main amplifier arrangement. As a further study we have obtained an increased slope efficiency of 40% and an optical-to-optical efficiency of 30% using a pinhole vacuum spatial filter/image relay for laser mode control. With 1.8 mJ input seed pulses, output pulse energies of around 150 mJ were achieved.     

A 61-mJ, 1-kHz cryogenic Yb: YAG laser amplifier

We report a diode-pumped rod-type Yb:YAG laser amplifier operating at 1 kHz. Cryogenic cooling method was adopted to make the Yb:YAG crystal work with four-level behavior. A single-frequency fiber laser acts as the seed in an actively Q-switched Yb:YAG oscillator. The resonator delivers 5.75-mJ pulses at 1 kHz with a pulse duration of approximately 40 ns. The pulses were amplified to 61 mJ in a four-pass rod-type Yb:YAG amplifier with optical-to-optical efficiency of 24% in the main amplifier. The M² parameter of the output laser is <1.4.     

Demonstration of a compact 100 Hz, 0.1 J, diode-pumped picosecond laser

We have demonstrated an all-diode-pumped Yb:YAG chirped pulse amplification laser that produces 100 mJ pulses of 5 ps duration at 100 Hz repetition rate. The compact laser system combines a room-temperature Yb:YAG regenerative amplifier for increased bandwidth and a cryogenically cooled Yb:YAG four-pass amplifier for improved heat dissipation and increased efficiency. The optical efficiency of this amplifier is higher than that of other diode-pumped systems of comparable energy.     

Efficient femtosecond Yb:YAG laser pumped by a single-mode laser diode

Single-mode diodes enable a particularly simple, compact and effective pumping of solid-state laser devices for many specialized applications. We investigated a single-mode, 300-mW laser diode for pumping at 935 nm a Yb:YAG laser passively mode-locked by a semiconductor saturable absorber. Relatively short pulse generation (156 fs), tunable across 1033–1059 nm has been demonstrated. An optical-to-optical efficiency of about 28% has been obtained with 320 fs long pulses. Therefore, contrarily to what previously believed, compact diode-pumped ultrafast Yb:YAG oscillators can reliably and efficiently deliver pulses in the range of ≈ 100–200 fs with few tens of mW, which are very appealing for bio-diagnostics and amplifier seeding applications.     

Parametric Amplification of Phase‐Locked Few‐Cycle Pulses and Ultraviolet Harmonics Generation in Solids at High Repetition Rate

A high‐power femtosecond Yb:fiber system is seeded by a phase‐locked Er:fiber source and drives an ultra‐broadband optical parametric amplifier that operates at 10 MHz repetition rate. The resulting pulses display precise control of the carrier‐envelope phase. Their 8.3 fs temporal duration corresponds to 2.3 optical cycles of the 1100 nm carrier wavelength. Focusing 200 nJ of pulse energy into widegap materials generates optical harmonics up to fifth order. Even in a perturbative regime, strong effects of the carrier‐envelope phase on the emitted spectra are observed.     

Multi-millijoule, nonlinear preamplifier for high intensity femtosecond Yb:YAG chirped-pulse amplification lasers at 1030 nm

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.     

Fast wavelength-switching of a diode-pumped solid-state disk laser

The functionality of two experimental setups for fast wavelength-switching of an Yb:YAG disk laser is tested and characterized. The first setup consists of two resonators sharing one disk. Both resonators are alternately opened by a chopper disk. Each resonator is tuned independently by a set of a two-stage Lyot filter and an etalon. Up to 1500 Hz the setup can switch between two freely selectable wavelengths (linewidth (fwhm) ≪1 pm) within the complete Yb:YAG tuning range (from 1020 nm to 1055 nm) emitting a maximum average power of 105 mW. The power of both resonators differs by a factor of 0.7. Their pointing stability amounts to 20 μrad. The second setup consists of a single tunable resonator (two-stage Lyot filter, etalon) additionally equipped with an electro-optical device (Faraday rotator or Pockels cell) providing a high pointing stability of better than 1 μrad. The wavelength switches occur stepwise and are predetermined by the etalon (about 90 pm or multiples thereof). The Faraday rotator suffers from its high thermal load and operates for some few 10 s only at 0.5 Hz. The resonator with the Pockels cell provides long term stability at 1000 Hz, switching steps up to 1.1 nm and a power ratio of 0.83 for the selected wavelengths.     

High energy Yb:YAG active mirror laser system for transform limited pulses bridging the picosecond gap

A diode‐pumped Yb:YAG MOPA‐System for the unprecedented generation of transform limited pulses with variable pulse duration in the range between 10 ps and 100 ps is presented. First applications relying on unique pulse parameters as modulation free spectrum, tunability and coherence length, namely the direct laser interference patterning (DLIP) and laser cooling of stored relativistic ion beams are highlighted. Pulses are generated by a mode‐locked fs‐oscillator while the spectral bandwidth is narrowed in the subsequent regenerative amplifier by an intra‐cavity grating monochromator. Two alternative booster amplifiers were added to increase the pulse energy to 100 μJ and 10 mJ, respectively.

     

Generation of 287 W, 5.5 ps pulses at 78 MHz repetition rate from a cryogenically cooled Yb:YAG amplifier seeded by a fiber chirped-pulse amplification system

We generate linearly polarized, 287 W average-power, 5.5 ps pulses using a cryogenically cooled Yb:YAG amplifier at a repetition rate of 78 MHz. An optical-to-optical efficiency of 41% is obtained at 700 W pump power. A 6 W, 0.4 nm bandwidth picosecond seed source at 1029 nm wavelength is constructed using a chirped-pulse fiber amplification chain based on chirped volume Bragg gratings. The combination of a fiber amplifier system and a cryogenically cooled Yb:YAG amplifier results in good spatial beam quality at large average power. Low nonlinear phase accumulation as small as 5.1 x 10(-3) rad in the bulk Yb:YAG amplifier supports power scalability to a > 10 kW level without being affected by self-phase modulation. This amplification system is well suited for pumping high-power high-repetition-rate optical parametric chirped-pulse amplifiers.     

High energy femtosecond OPA pumped by 1030 nm Yb:KGW laser.

We present a traveling-wave-type optical parametric amplifier (OPA) pumped at 1.03 μm by a Yb:KGW laser that produces tunable high-energy pulses of 6.5–4 μJ in the mid-infrared (mid-IR) region from 3.6 to 7 μm. Pumping with negatively chirped pulses generates nearly transform-limited (TL) mid-IR pulses of 300–330 fs length. Pumping with TL pulses of 200 fs not only decreases the output energy by a factor of 1.5, but also decreases the mid-IR pulse-length to 160 fs after additional compression. The compact and simple OPA setup is ideal for femtosecond infrared experiments in the fingerprint region.     

Sub-kHz cryogenic Yb:YAG regenerative amplifier by using a total-reflection active mirror

The first pulse operation using a total-reflection active mirror (TRAM) with a cryogenic Yb:YAG/YAG monolithic composite ceramics was demonstrated in a regenerative amplifier scheme. More than 5.0 mJ of output pulse energy was obtained for repetition rates between 10 and 450 Hz. A high energy fluence of 3.5 J/cm² on the active media was realized by separating input and output surfaces of the TRAM.     

Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG

A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps. The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG.     

Direct amplification of ultrashort pulses in μ-pulling-down Yb:YAG single crystal fibers

We demonstrated that Yb:YAG single crystal fibers have a strong potential for the amplification of femtosecond pulses. Seeded by 230?fs pulses with an average power of 400?mW at 30?MHz delivered by a passively mode-locked Yb:KYW oscillator, the system produced 330?fs pulses with an average power of 12?W. This is the shortest pulse duration ever produced by an Yb:YAG amplifier. The gain in the single crystal fiber reached a value as high as 30 in a simple double-pass configuration.     

Hundred mJ, sub-picoseconds, high temporal contrast OPCPA/Yb:YAG ceramic thin disk hybrid laser system

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.     

Generation of 220 mJ nanosecond pulses at a 10 Hz repetition rate with excellent beam quality in a diode-pumped Yb:YAG MOPA system

A novel all-diode-pumped master oscillator power amplifier system based on Yb:YAG crystal rods has been developed. It consists of a Q-switched oscillator delivering 3 mJ, 6.4 ns pulses at a 10 Hz repetition rate and an additional four-pass amplifier, which boosts the output energy to 220 mJ, while a close to TEM(00) beam quality could be observed. Additionally a simulation of the amplification was written that allows for further scaling considerations.     

Highly efficient cryogenically-cooled Yb:YAG laser

A MOPA laser system for high pulse energy and high average power has been developed by using a cryogenic Yb:YAG. In the regenerative amplifier with our original TRAM architecture, the high pulse energies of 6.5 and 1.5 mJ were obtained at the repetition rate of 200 Hz and 1 kHz, respectively. An optical efficiency was as high as η_o-o = 9.3% with an excellent beam quality of M ² < 1.1, which ensured that a cryogenic Yb:YAG TRAM had a high thermal strength. The following four pass power amplifier with a cryogenic Yb:YAG rod showed 140 mJ at 100 Hz. Both a high optical efficiency of η_o-o = 30% and a high slope efficiency of η_s = 44% showed that an efficient laser operation could be realized for a power amplification with both a high pulse energy and a high average power by using a cryogenic Yb:YAG.     

High-energy Q-switched operation of a fiber-laser-pumped Er:YAG laser

A high-energy Q-switched Er:YAG laser in-band pumped by an Er,Yb co-doped fiber laser is reported. A simple two-mirror multi-mode resonator incorporating an electro-optic Q-switch and a multi-Brewster-plate polarizer was employed, together with a simple compensation scheme to reduce the depolarization loss due to thermally induced stress birefringence in the Er:YAG crystal at high pump powers. The laser yielded Q-switched pulses at 1617 nm with 30.5-mJ pulse energy and <20-ns pulse duration (FWHM) at 20-Hz repetition rate, corresponding to a peak power of >1.5 MW for 55 W of pump power at 1532 nm. The prospects for further improvement in Q-switched performance are discussed.     

Laser-diode-pumped Yb:YAG laser as a new pump source and its application to an Er3+, Yb3+-codoped high-output-power fiber amplifier

We propose a laser-diode-pumped Yb:YAG laser as a novel practical fiber amplifier pump source, and describe its first successful application of high-output-power operation (850 mW=+29.3 dB m) of an Er³⁺,Yb³⁺-codoped fiber amplifier at 1.55 μm. We have developed both bulk and microchip Yb:YAG lasers and obtained 3.3 W and 2.7 W, respectively, in the cw mode at room temperature. Laser-diode-pumped Yb:YAG lasers are shown to have a potential applicability to such fiber amplifiers as Pr³⁺-doped amplifiers and Tm³⁺-doped amplifiers, as well as Er³⁺,Yb³⁺-codoped fiber amplifiers. Received: 12 August 1999 / Revised version: 3 September 1999 / Published online: 20 October 1999     

Picosecond pulse contrast enhancement by use of polarization rotation in crystals with the second-order nonlinearity

We report on the implementation of intensity-dependent filter for picosecond pulse temporal cleaning based on an effect of pulse polarization rotation during the unbalanced phase matched second harmonic generation. The pulse contrast enhancement by more than two orders of magnitude and filter transmission of ∼25% has been demonstrated at pulse intensities of <1 GW/cm². A simple and reliable all-solid-state filter scheme was integrated in a two-stage picosecond Nd:YAG regenerative amplifier seeded with pJ-energy femtosecond pulses of the Yb:KGW oscillator, and allowed us to reduce the ASE intensity level down to 1.5×10⁻⁸ with reference to the intensity of main 100 ps and 100 μJ pulse.     

High-efficiency 10 J diode pumped cryogenic gas cooled Yb:YAG multislab amplifier

We report on the first demonstration of a diode-pumped, gas cooled, cryogenic multislab Yb:YAG amplifier. The performance was characterized over a temperature range from 88 to 175 K. A maximum small-signal single-pass longitudinal gain of 11.0 was measured at 88 K. When amplifying nanosecond pulses, recorded output energies were 10.1 J at 1 Hz in a four-pass extraction geometry and 6.4 J at 10 Hz in a three-pass setup, corresponding to optical to optical conversion efficiencies of 21% and 16%, respectively. To our knowledge, this represents the highest pulse energy so far obtained from a cryo-cooled Yb-laser and the highest efficiency from a multijoule diode pumped solid-state laser system.