On the performance of short pulse Nd3+:LSB microchip lasers

Experimental results from studies of the laser characteristics of Nd:LSB crystals in both cw and passive Q-switching arrangements are presented. The dependence of the main laser parameters on the output coupling and saturable absorber transmission for two doping levels of Nd was investigated. It is demonstrated that due to its high absorption, low losses and intrinsic strong thermal lensing, even at pump powers of less than 200 mW, the Nd:LSB has excellent properties in terms of efficiency, beam quality and pulse duration. In addition, it exhibits high pulse-to-pulse and pulse width versus pump power stability. Received: 11 June 2001 / Revised version: 30 July 2001 / Published online: 15 October 2001     

Stable high-power continuous-wave Yb(3+)-doped silica fiber laser utilizing a point-by-point inscribed fiber Bragg grating

We report on a narrowband 5 W cw fiber laser incorporating a point-by-point fiber Bragg grating inscribed into the core of a Yb(3+)-doped double-clad fiber. The laser featured excellent long-term wavelength and power stability (0.3%), as well as a very narrow (15 pm) linewidth, when passive temperature stabilization of the grating was implemented.     

Efficient power scaling of laser radiation by spectral beam combining

The possibility of achieving multikilowatt laser radiation by spectrally combining beams using volume Bragg gratings (VBGs) is shown. The VBGs recorded in a photothermorefractive glass exhibit long-term stability of all its parameters in high-power laser beams with power density >1 MW/cm2 in the cw beam of total power on a kilowatt level. We consider an architecture-specific beam-combining scheme and address the cross-talk minimization problem based on optimal channel positioning. Five-channel high efficiency spectral beam combining resulted in a >750 W near-diffraction-limited cw beam has been demonstrated experimentally.     

Precise frequency transfer through a fiber network by use of 1.5-microm mode-locked sources

We report the precise transfer of radio-frequency signals by use of the pulse repetition frequency of mode-locked laser sources at 1.5 microm transmitting through a fiber network. The passive transfer instability through a 6.9-km fiber is below 3 x 10(-14) at 1 s, which is comparable with the optical carrier-frequency transfer of a narrow-linewidth cw laser. The instability of the measurement system is below 7 x 10(-15) at 1 s. It is noted that the pulsed mode of operation offers almost an order-of-magnitude improvement in stability at 1 s over that with a sinusoidal amplitude modulation on an optical carrier.     

New efficient laser dye for pulsed and CW operation in the UV

A new laser dye for pulsed and cw operation has been synthesized which can be tuned from 362 nm up to 412 nm. For pulsed excitation with a XeCl excimer laser an energy conversion of 18.5% has been measured at the tuning maximum of the dye; this is the highest efficiency for any known dye in the UV. For cw operation a low laser threshold and a goof efficiency have been observed. The range of tuned cw dye lasers is extended by 30 nm to shorter wavelengths. The dye shows high photochemical stability even at high pump laser power.     

A continuous wave SrMoO4 Raman laser

We demonstrate a cw, laser diode-pumped Nd:GdVO4/SrMoO4 crystalline Raman laser. First Stokes laser output at 1173.5?nm of 2.18?W was achieved with a diode-to-first Stokes efficiency of 8.7%. With intracavity frequency doubling in LiB3O5, 3.1?W of cw yellow emission at 586.8?nm was obtained with a 12.4% diode-to-yellow efficiency. The experimental results show that SrMoO4 is an excellent stimulated Raman scattering gain material for high-power cw near-IR Stokes and yellow lasers.     

Precision phase control of an ultrawide-bandwidth femtosecond laser: a network of ultrastable frequency marks across the visible spectrum

We demonstrate that the stability of the current optical frequency comb generated by a Kerr-lens mode-locked femtosecond laser is limited by the microwave reference used for phase locking the comb spacing. Hence we implement precision frequency/phase control of the entire comb to the fundamental and second-harmonic frequencies of a stable cw laser without any external microwave reference. The stability of a cw iodine-stabilized laser is transferred to millions of comb lines (with an instability of 3 x 10(-13)) covering more than one octave of the optical frequency spectrum. In addition, the mode spacing of the comb can be used as a stable microwave frequency derived directly from a stable optical oscillator.     

Visible upconversion lasers in praseodymium-ytterbium-doped fibers

We report on a ZBLAN-fiber-based praseodymium-ytterbium-doped upconversion fiber laser operating in the blue-green with diffraction-limited beam quality. cw output powers of more than 150 mW at 491 nm are achieved for several hours without degradation. The spectroscopic data of the active material and laser parameters including the amplitude noise are discussed. Received: 28 June 1999 / Revised version: 20 August 1999 / Published online: 20 October 1999     

High power cw dye lasers

The dependance of the output power of cw dye lasers on the pump power and the system-and stream parameters is calculated and experimentally tested. It was found that the pump power for a given system is limited to a critical value due to the influence of thermal inhomogeneities. This critical pump power is predominantly dependant on the dye solvent, the flow velocity, the focussing of the pump laser and the stability range of the dye laser system. Possibilities for the reduction of the thermal inhomogeneities are discussed and attainable output powers are calculated.     

Passively Mode-Locked Quasi-Three-Level Nd:LuVO4Laser with Semiconductor Saturable Absorber Mirror

We demonstrate a passively a Z-folded resonator. Using device, we achieve stable cw average output power under cw mode-locked Nd：LuVO4 laser operating on the quasi-three-level at 916nm with a semiconductor saturable absorber mirror （SESAM） as the passive mode-locking mode locking with 6.7ps pulse duration at repetition rate of 133 MHz and 88mW the pump power of 17.1 W.     

Laser performance and stability of fluorinated coumarin dyes

Several new coumarin derivatives are reported and their relative photochemical stability under flash and cw excitation is investigated. There seems to be no simple relation between the cw bleaching rate and the number of laser shots obtainable from any particular dye solution.     

High-power, continuous-wave, mid-infrared optical parametric oscillator based on MgO:sPPLT

We report a stable, high-power, cw, mid-IR optical parametric oscillator using MgO-doped stoichiometric periodically poled LiTaO? (MgO:sPPLT) pumped by a Yb fiber laser at 1064 nm. The singly resonant oscillator (SRO), based on a 30 mm long crystal, is tunable over 430 nm from 3032 to 3462 nm and can generate as much as 5.5 W of mid-IR output power, with >4 W of over 60% of the tuning range and under reduced thermal effects, enabling room temperature operation. Idler power scaling measurements at ~3.3 μm are compared with an MgO-doped periodically poled LiNbO? cw SRO, confirming that MgO:sPPLT is an attractive material for multiwatt mid-IR generation. The idler output at 3299 nm exhibits a peak-to-peak power stability better than 12.8% over 5 h and frequency stability of ~1 GHz, while operating close to room temperature, and has a linewidth of ~0.2 nm, limited by the resolution of the wavemeter. The corresponding signal linewidth at 1570 nm is ~21 MHz.     

Theory of active-passive mode-locking of solid-state lasers using a nonlinear mirror

The theory of active-passive mode-locked solid-state lasers is developed where the passive mode-locking is achieved by a nonlinear mirror. Steady-state cw numerical solutions are analyzed in detail for the case of a Nd: YAG laser. The steady-state pulse duration can be reduced by an order of magnitude as compared to the pure active mode-locking regime.On leave from Department of Quantum Electronics, Faculty of Physics, University of Sofia, BG-1126 Sofia, Bulgaria     

cw dual-wavelength operation of a diode-end-pumped Nd:YVO4 laser

A dual-wavelength continuous wave (cw) diode-end-pumped Nd:YVO₄ laser that generates simultaneous laser action at the wavelengths 1064 nm and 1342 nm is demonstrated. The optimum oscillation condition for the simultaneous dual-wavelength operation in a diode-end-pumped solid-state laser has been derived. The relationship between the laser cavity and the output stability is also studied. Experimental results show that the stability of the output power at the two wavelengths could be enhanced by use of a three-mirror cavity. Received: 26 August 1999 / Revised version: 11 October 1999 / Published online: 23 February 2000     

Passive mode locking of lasers by crossed-polarization gain modulation

We report on a novel approach for inducing passive mode locking of lasers without using any saturable absorber but exploiting the polarization degree of freedom of light. In our scheme, passive mode locking is achieved by crossed-polarization gain modulation caused by the reinjection of a polarization-rotated replica of the laser output after a time delay. The reinjection time delay defines resonance tongues that correspond to mode-locking operation. Numerical continuation reveals that the cw solution is destabilized through a Hopf bifurcation that defines the onset of multimode operation which evolves sharply into a mode-locked solution. Our approach can be applied to a large variety of laser systems. For vertical-cavity surface-emitting lasers, we demonstrate stable mode-locked pulses at repetition rates in the GHz range and pulse widths of few tens of picoseconds.     

Continuous oscillation of a (Sc,Nd) pentaphosphate laser with 4 milliwatts pump threshold

We report on room temperature cw oscillation of a scandium neodymium pentaphosphate (Sc: NdP₅O₁₄) laser pumped with an argon laser. The threshold pump power is, to our knowledge, the lowest obtained so far at room temperature with any laser material.     

Multicrystal, continuous-wave, single-pass second-harmonic generation with 56% efficiency

We report a simple and compact implementation for single-pass second-harmonic-generation (SP-SHG) of cw laser radiation, based on a cascaded multicrystal (MC) scheme, that can provide the highest conversion efficiency at any given fundamental power. By deploying a suitable number of identical 30-mm-long MgO:sPPLT crystals in a cascade and a 30W cw Yb-fiber laser at 1064nm as the fundamental source, we demonstrate SP-SHG into the green with a conversion efficiency as high as 56% in the low-power as well as the high-power regime, providing 5.6W of green output for 10W and 13W of green output for 25.1W of input pump power. The MC scheme permits substantial increase in cw SP-SHG efficiency compared to the conventional single-crystal scheme without compromising performance with regard to power stability and beam quality.     

High-power self-mode-locked Yb:Y(2)O(3) ceramic laser

We have experimentally demonstrated a high-power self-mode-locked Yb:Y(2)O(3) ceramic laser. Without any additional active or passive element in the cavity, self-started cw mode-locking was achieved. The maximum output power was as high as 2.7 W with a pulse duration of 1.1 ps. Numerical studies show that the diffraction loss induced by thermal lens aberration, in combination with the Kerr self-focusing effect in the gain medium, results in the mode locking of the laser. To our knowledge, this is the first self-mode-locked ceramic laser.     

Stochastic analysis of synchroscan operations of a streak camera

This paper deals with a theoretical and experimental study of the picosecond synchronization of a streak camera used in conjunction with a cw actively mode-locked laser system. The temporal resolution of two synchronization set-ups, a passive device (sweep obtained directly from the mode-locker oscillator) and an active arrangement (deflection derived from the recurrent laser pulses through a photodiode and a tunnel diode) has been examined. On the basis of the stochastic analysis it has been possible to interpret the experimental results for both configurations: in particular, it has been demonstrated that even in the presence of phase noise in the laser signal, perfect synchronization can be achieved.     

New efficient and stable laser dyes for cw operation in the blue and violet spectral region

Sulphonated bis-styryles and triazinyl-stilbenes have been investigated for cw dye laser operation. These promising new classes of laser dyes have proven to be superior to the known coumarins with respect to threshold, slope efficiency and photochemical stability. They shift the short wavelength tuning limit of the cw dye laser down to 403 nm. Broad tuning ranges of more than 4500 cm^-1 and efficiencies up to 20% were found. In contrast to the coumarins these new dyes showed no photochemical degradation even at high pump power levels.