Electrically tunable Lyot filter for fast wavelength switching of?diode-pumped solid-state disk lasers

A new setup for fast wavelength switching of an Yb:YAG disk laser uses a lithium niobate Lyot filter. It is modeled by the Jones matrix formalism and it is tested experimentally. Applying a high voltage to the Lyot filter leads to stepwise wavelength switching of the laser with a minimum step size of 91 pm determined by the intra-cavity etalon ensuring longitudinal single-mode operation. The maximum step size achieved with the current driving electronics amounts to 0.6 nm at 500 Hz switching frequency. This setup shows high spatial and temporal laser beam stabilities.     

Axial mode tuning of a single frequency Yb:YAG thin disk laser

We describe an arrangement for an Yb:YAG thin disk laser, which enables narrow bandwidth operation in single-frequency mode at freely selectable wavelengths within the broad tuning range of the laser. This is facilitated by a combination of a double-stage birefringent filter and an etalon inside the laser cavity. We investigate the wavelength selection characteristics of the single elements as well as their combination. A simple procedure is implemented for a computer-based automation of wavelength tuning. The reflectivity of the partially reflecting resonator mirror is optimised, and the laser pump power is adapted for best tuning performance. Single-frequency emission is achieved in a frequency range of 9.75 THz (wavelength range 1020 nm to 1055 nm). Each axial laser mode in this range can be selected individually. The axial mode separation of 0.47 GHz corresponds to wavelength steps of 1.7 pm at 1030 nm. PACS 42.55.Xi; 42.60.Fc; 42.60.Lh     

4.44 W of CW 515 nm green light generated by intracavity frequency doubling Yb:YAG thin disk laser with LBO

We demonstrate the generation of 515 nm green laser with diode-pumped Yb:YAG thin disk by intracavity frequency doubling of type-I phase-matched LiB₃O₅(LBO) in a V-type cavity at room temperature. A continuous-wave (CW) output power of 4.44 W at 515 nm was obtained. Optical-optical efficiency of 515 nm green laser is 14.6%. The fluctuation of green laser was 1.6% at the maximum output power in 0.5 h. Thermal lensing effects in Yb:YAG thin disk are investigated too.     

Role of optical resonator on the pointing stability of copper vapor laser beam

This paper presents a first comprehensive study on the pointing stability of copper vapor laser with an emphasis on bringing out the role of optical resonator. Long term (∼10 min), single pulse, far-field beam pointing stability of a 5.5 kHz repetition rate copper vapor laser (λ = 510 nm) with plane-plane, unstable and filtering resonators, is studied. It is established that the resonator optics largely decides the CVL pointing stability. Minimum beam pointing angle of 8 μrad from generalized diffraction filtered resonator (GDFR) is obtained in contrast to a maximum value of 120 μrad from the plane-plane resonator. The unstable resonators data is in between. The relative trends in CVL pointing stability are discussed in terms of wave-front distortions due to resonator mode build up from optical noise, thermal and mirror misalignment effects. The degree of optical resonator immunity to phase distortions dictates the net pointing stability achieved.     

A diode-pumped, frequency-doubled, tunable single-mode quasi-continuous-wave Yb:YAG laser emitting 70 W peak power at 515 nm

An efficient pumping scheme for a quasi-continuous-wave diode-pumped Yb:YAG laser is presented. Single-mode operation and fine wavelength tuning are assured by the use of a rubidium titanyl phosphate (RTP) Fabry–Perot étalon. When frequency doubled, the 200–420 μs duration pulses reach a peak power of 70 W at a wavelength of 515 nm. The TEM₀₀ beam is nearly diffraction limited with an M ² factor of 1.06 at full power. The tuning range spans from 512 to 520 nm and the pulse to pulse frequency stability is on the order of ±10 MHz. Laboratoire Aimé Cotton is associated with Université Paris Sud 11.     

Development of a Joule‐class Yb:YAG amplifier and its implementation in a CPA system generating 1 TW pulses

In this paper the development and implementation of a novel amplifier setup as an additional stage for the CPA pump laser of the Petawatt Field Synthesizer, currently developed at the Max‐Planck‐Institute of Quantum Optics, is presented. This amplifier design comprises 20 relay‐imaged passes through the active medium which are arranged in rotational symmetry. As the gain material, an in‐house‐developed Yb:YAG active‐mirror is used. With this setup, stretched 4 ns seed pulses are amplified to output energies exceeding 1 J with repetition rates of up to 2 Hz. Furthermore, a spectral bandwidth of 3.5 nm (FWHM) is maintained during amplification and the compression of the pulses down to their Fourier‐limit of 740 fs is achieved. To the best of our knowledge, this is the first demonstration of 1 TW pulses generated via CPA in diode‐pumped Yb:YAG.     

Intermittent oscillation of 1064 nm and 1342 nm obtained in?a?diode-pumped doubly passively Q-switched Nd:YVO4 laser

The intermittent oscillation of 1064 nm and 1342 nm was demonstrated in a diode-pumped doubly passively Q-switched Nd:YVO₄/Cr⁴⁺:YAG/V³⁺:YAG laser for the first time to our best knowledge. By exploiting a three-mirror configuration and choosing appropriate reflectivity values for the two wavelengths on the output couplers, the dual-wavelength pulsed operation was obtained. The maximum dual-wavelength average output power was 428 mW, corresponding to an optical-to-optical conversion efficiency of 8.5%. The corresponding physical explanations for the intermittent oscillation as well as the related phenomena are also given in this paper.     

Folded diffractive laser resonators with user-defined fundamental mode

The adjustment effort required for the alignment of laser resonators with arbitrarily shaped end mirrors can be significantly reduced by folding the resonator path half-way between the two end mirrors and by slightly tilting the resonator axis. Thus the resulting resonator consists only of one diffractive mirror and a plane mirror, and the separate alignment of both diffractive end mirrors with respect to each other can be avoided. This principle is demonstrated by a Nd:YAG laser with super-Gaussian output beam. Furthermore, it is shown theoretically that the influence of phase quantization effects on the beam quality can be strongly reduced as a consequence of the tilted resonator axis.     

Collinear and non-collinear sum-frequency mixing inβ-BBO for a tunable 195–198 nm all-solid-state laser system

We attained tunable UV laser radiation between 195 and 198 nm by sum-frequency mixing two synchronized flashlamp-pumped solid-state Q-switch lasers, a Nd:YAG laser frequency quadrupled to 266 nm and a tunable (730–770 nm) alexandrite laser. UV pulse energies of 0.12 mJ with repetition rates of 10 Hz were attained in collinear, as well as non-collinear sum-frequency interaction in a-Barium Borate (BBO) crystal with a conversion efficiency of 2.5%. Theoretical models for the non-collinear phase-matching interaction were investigated at UV wavelengths below 200 nm.     

Single mode oscillation of TEA CO2 laser with an interference resonator

An effective single-longitudinal mode (SLM) pulse TEA CO₂ laser operation was demonstrated using a Michelson’s type resonator with a tilting Fabry-Perot etalon. A modified numerical model of the interference resonator was investigated for designing the laser. The experimentally measured values were found to have good agreement with the numerical model. A pulse width of about 90 ns and the maximum pulse energy of about 300 mJ were achieved at 10.59 μm in SLM and TEM₀₀ mode. The reliability of producing SLM pulses was 100% and there was no damage on the etalon. By turning the interference resonator, the SLM output was tuned 44 lines of the CO₂ spectrum.     

Noise characteristics of a high-power ytterbium-doped fibre amplifier at 1083 nm

Experimental results are reported for the noise characteristics of an Yb-doped fibre amplifier pumped at 975 nm, used as a booster of a low-noise narrow-linewidth single-frequency 1083-nm wavelength laser diode. The maximum output power of the amplifier is 1.2 W with a gain larger than 30 dB. An increase of the intensity-noise spectral density relative to the signal, by approximately 6.5 dB, is introduced by the amplification process, due to signal-amplified spontaneous-emission (ASE) beat noise. A remarkable increase of the noise level with decreasing frequency is observed below ≈35 kHz, probably due to technical noise of the amplifier pump diodes. The spectral broadening due to amplifier phase noise was measured to be less than 300 Hz with a 5-kHz-linewidth Nd:YAG laser and that for the 300-kHz-linewidth diode laser at 1083 nm is therefore expected to be in the same range. Received: 5 October 1999 / Revised version: 2 December 1999 / Published online: 24 March 2000     

High-beam-quality, 5.1 J, 108 Hz diode-pumped Nd:YAG rod oscillator-amplifier laser system

A high efficiency, high beam quality diode-pumped Nd:YAG master oscillator power-amplifier (MOPA) laser with six amplifier stages is demonstrated. The oscillator with two-rod birefringence compensation was designed as a thermally determined near hemispherical resonator, which presents a pulse energy of 223 mJ with a beam quality value of M² = 1.29 at a repetition rate of 108 Hz. The MOPA system delivers a pulse energy of 5.1 J with a pulse width of 230 μs, a M² factor of 3.6 and an optical-to-optical efficiency of 38.5%. To the best of our knowledge, this is the highest pulse energy for a diode-pumped Nd:YAG rod laser operation with a high beam quality and a pulse width of hundreds of microseconds at a repetition rate of over 100 Hz.     

Diode-pumped laser with Yb:YAG single-crystal fiber grown by the micro-pulling down technique

Laser emission obtained from an Yb:YAG single-crystal fiber directly grown by the micro-pulling down technique is demonstrated for the first time. We achieved 11.2 W of continuous wave (CW) output power at 1031 nm for 55 W of incident pump power at 940 nm. In the Q-switched regime, we obtained pulses as short as 17 ns, for an average power of 2.3 W at 2 kHz corresponding to an energy of 1.15  mJ. In both cases, the M ² factor was 2.5. This single-crystal fiber showed performance similar to a standard rod elaborated by the Czochralski method. The potential of Yb³⁺-doped single-crystal fibers is presented for scalable high-average and high-peak-power laser systems.     

Passively Q-switched Nd:YAG pumped UV lasers at 280 and 374 nm

Pulsed UV lasers at the wavelengths of 374 and 280 nm are realized by cascaded second harmonic generation (SHG) and sum frequency generation (SFG) processes using a Nd:YAG laser at 1123 nm. The Nd:YAG laser is longitudinally pumped and passively Q-switched, and it has a high peak power of 3.2 kW. The UV peak powers at 280 and 374 nm are 100 and 310 W, with pulse lengths of 6 and 8 ns, respectively. Spectral broadening of 374 nm laser by stimulated Raman scattering is studied in single mode pure silica core UV fiber. Realizations of UV lasers enabling compact design at 280 and 374 nm wavelengths are demonstrated.     

Intracavity frequency-doubled diode-pumped Nd : LaSc3(BO3)4 lasers

 An intracavity frequency-doubled 10%Nd : LaSc₃(BO₃)₄ (Nd : LSB) laser was investigated in different resonator configurations and in different operation modes under continuous wave (cw) and quasi-cw laser-diode pumping. With a Cr⁴⁺ : YAG passive modulator and a KTP crystal the second-harmonic output power at 531 nm amounted to 190 mW in Q-switched TEM₀₀ mode at 750 mW of pump power. In a sandwich resonator, when all the optical elements were in direct contact with each other, 0.8 W of green output power was obtained in cw mode under 2.7 W of pump power with a slope efficiency of 44%. In the same setup under fiber-coupled diode-laser array pumping (5.6 W of incident power), 1.2 W of green output power was achieved in cw mode and 1.4 W in quasi-cw mode. Received: 30 April 1996/Revised version: 1 July 1996     

Liquid-cooled ceramic Nd:YAG split-disk amplifier for high-average-power laser

A liquid-cooled ceramic Nd:YAG split-disk laser amplifier has been designed for a high-average-power laser system. The maximum average output power of 17.1 W (1.71 J at 10 Hz) and the beam size of far-field pattern with 1.5 times diffraction limit was obtained. The combination of liquid cooling for disk laser material and wavefront compensation with a phase conjugation mirror was demonstrated. The wavefront degradation by liquid cooling was observed and measured with Michelson interferometer and far-field patterns.     

Diode-end-pumped linear-polarized single-frequency Tm:YAG laser at room temperature

By using two solid uncoated etalons, we present a diode-pumped linear-polarized single-frequency Tm:YAG laser operating at 2 μm. Placing one 0.1 mm F-P etalon at nearly Brewster angle in the cavity, the linear-polarization laser is achieved. The other 1 mm F-P etalon was turned in the range of very small angle, single-longitudinal-mode (SLM) could be obtained. The maximum output power of linear-polarized single-frequency laser of 60 mW is achieved at the wavelength of 2013 nm. The degree of the polarization is over 30 dB. Long-term frequency stability was also investigated, with the results of wavelength fluctuation about 2.55 × 10⁻¹³ m within 3 min and frequency change about 18.86 MHz, corresponding to a frequency stability of 1.27 × 10⁻⁷.     

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.     

Spectral properties of a Tm:Ho:YAG laser in active mirror configuration

3+ :Ho³⁺:YAG laser is operated in active mirror configuration. This laser is characterised by a rather thin crystal (3 mm thickness in our experiment) and a very short resonator (about 3.2 mm). Therefore this laser is well suited for operation in a single longitudinal mode. Single-frequency operation is demonstrated with and without an intracavity etalon. It is further shown that single-frequency emission is reached with a stable cw emission. With a slight detuning of the outcoupling mirror, spiking can be achieved, resulting in an emission on different lines. The assignment of the observed laser lines to the known transitions between Stark sublevels of the ⁵I₇ and the ⁵I₈ level is discussed and compared with predictions in the literature. Received: 2 December 1997     

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