High-power, high repetition-rate, green-pumped, picosecond LBO optical parametric oscillator.

We report on a picosecond, green-pumped, lithium triborate optical parametric oscillator with record-high output power. It was synchronously pumped by a frequency-doubled (530 nm), pulse-compressed (4.4 ps), high-repetition-rate (230 MHz), fiber-amplified gain-switched laser diode. For a pump power of 17 W, a maximum signal and idler power of 3.7 W and 1.8 W was obtained from the optical parametric oscillator. A signal pulse duration of ~3.2 ps was measured and wide tunability from 651 nm to 1040 nm for the signal and from 1081 nm to 2851 nm for the idler was achieved.

High energy femtosecond fiber chirped pulse amplification system with adaptive phase control.

We demonstrate increased peak power from an Yb fiber CPA system operating with strong self-phase modulation by shaping the spectral-phase of the input pulses. An adaptive control loop used feedback from the output autocorrelation. We investigated pre-compensation of both SPM phase distortion at high energies, and residual dispersion from mismatched stretcher/compressor technologies at low energies. Phase shaping resulted in improved pulse quality. When using a bulk grating stretcher, shaping increased the autocorrelation peak by a factor of 2.9, and with a fiber stretcher, shaping increased the autocorrelation peak by a factor of 3.4. High-quality 800 fs, 65 microJ recompressed pulses were produced. This technique could benefit a wide variety of fiber amplifier systems and is self-optimising for operation at both low and high pulse energies.

High-power femtosecond fiber-feedback optical parametric oscillator based on periodically poled stoichiometric LiTaO3.

We demonstrate a synchronously pumped high-gain optical parametric oscillator with feedback through a fiber, using a passively mode-locked Yb:YAG thin-disk laser as a pump source. We obtain as much as 19-W average signal power at a wavelength of 1.45 microm in 840-fs pulses and 7.8 W of idler power at 3.57 microm. The repetition rate of the pulses is 56 MHz, and the transverse beam quality of the generated signal is M2 < 1.6.

Synchronously pumped CdSe optical parametric oscillator in the 9-10 microm region.

Continuous mode-locked operation of a singly resonant, synchronously pumped optical parametric oscillator (SPOPO) based on CdSe has produced idler output tuned over the range of 9.1-9.7 microm, the longest wavelength generated so far to our knowledge from a SPOPO. Average idler powers as high as approximately 70 mW are generated in the crystal. Tandem pumping with a diffraction-grating-tuned parametric oscillator in periodically poled lithium niobate provides a convenient and agile means of tuning the noncritically phase-matched CdSe device. The absence of any detrimental thermal effects in the CdSe crystal suggests that significant further power scaling should be possible, with idler tuning ranges extendable to cover 8-12 microm.

Synchronously pumped optical parametric oscillator driven by a femtosecond mode-locked fiber laser.

A femtosecond all-fiber laser source incorporating a cw mode-locked Yb-doped silica fiber oscillator and amplifier has been used to synchronously pump an optical parametric oscillator based on periodically poled lithium niobate. The signal output, consisting of 330-fs pulses at a 54-MHz repetition rate and average powers up to 90 mW, was tuned from 1.55 to 1.95microm , with a corresponding idler range of 2.30-3.31microm .

High-power cladding-pumped Tm-doped silica fiber laser with wavelength tuning from 1860 to 2090 nm.

A high-power double-clad Tm-doped silica fiber laser, pumped by two beam-shaped and polarization-coupled diode bars at 787 nm, was wavelength tuned by use of an external cavity containing a diffraction grating. The Tm fiber laser produced a maximum output power of 7 W at 1940 nm for 40 W of incident diode power and was tuned over a wavelength range of 230 nm from 1860 to 2090 nm, with >5-W output power over the range 1870-2040 nm. The prospects for further improvement in performance and extension of the tuning range are discussed.

Extended operation of synchronously pumped optical parametric oscillators to longer idler wavelengths.

A synchronously pumped optical parametric oscillator, based on periodically poled lithium niobate, has operated at idler wavelengths out to 7.3 microm . Directly measured idler output powers (average) are 4.2 mW at 6.1 microm, 0.5 mW at 7.0 microm, and 0.04 mW at 7.25 microm . Characterization of the idler output indicates essentially bandwidth-limited and diffraction-limited operation.

Femtosecond fiber-feedback optical parametric oscillator.

We demonstrate what is to our knowledge the first synchronously pumped high-gain optical parametric oscillator (OPO) with feedback through a single-mode fiber. This device generates 2.3-2.7 W of signal power in 700-900-fs pulses tunable in a wavelength range from 1429 to 1473 nm. The necessary high gain was obtained from a periodically poled LiTaO(3) crystal pumped with as much as 8.2 W of power at 1030 nm from a passively mode-locked Yb:YAG laser with 600-fs pulse duration and a 35-MHz repetition rate. The fiber-feedback OPO setup is compact because most of the resonator feedback path consists of a standard telecom fiber. Because of the high parametric gain, the fiber-feedback OPO is highly insensitive to intracavity losses. For the same reason, the synchronization of the cavity with the pump laser is not critical, so active stabilization of the cavity length is not required.

Generation of femtosecond pulses from order-of-magnitude pulse compression in a synchronously pumped optical parametric oscillator based on periodically poled lithium niobate.

We demonstrate the generation of compressed, transform-limited 250-fs pulses, tunable in the near infrared, by means of synchronously pumped optical parametric oscillation in periodically poled lithium niobate. The almost 20-fold compression from the 4-ps pulse duration of the cw mode-locked Nd:YLF pump results in signal peak powers well in excess of the pump power.

Second-harmonic generation in a direct-bonded periodically poled LiNbO(3) buried waveguide.

We report the fabrication of a 12-mum -thick periodically poled LiNbO(3) planar waveguide buried in LiTaO(3) by direct bonding of precision-polished surfaces. Frequency doubling of the 1064-nm output of a cw diode-pumped Nd:YAG laser was performed in a 5.5-mm-long device with a 6.50-mum -period grating at an elevated temperature of 174 degrees C. The resultant green second-harmonic output exhibited fundamental-spatial-mode characteristics at a 4.3%W(-1) conversion efficiency.

Simple method for reducing the depolarization loss resulting from thermally induced birefringence in solid-state lasers.

A simple technique for reducing the loss that is due to depolarization resulting from thermally induced stress birefringence in solid-state lasers is reported. The technique uses a single intracavity quarter-wave plate with its fast or slow axis aligned parallel to the preferred plane of polarization, defined by an intracavity polarizer. This technique has been applied to a diode-bar-pumped Nd:YAG laser operating at 946 nm, resulting in a measured reduction in depolarization loss from approximately 1.7% to approximately 0.0006% and yielding a diffraction-limited, TEM(00) , linearly polarized output power of 2.9 W for an incident pump power of 14.3 W.

Parametric oscillator directly pumped by a 1.55-mum erbium-fiber laser.

We report what is believed to be the first demonstration of an optical parametric oscillator directly pumped by the 1.55-mum output of an erbium-doped fiber laser. The oscillator, based on periodically poled lithium niobate, produced 8-muJ idler output near 3.8 mum at a 500-Hz repetition rate when it was pumped with 100-muJ 60-ns pulses at 1.55 mum . Temperature tuning of the 50-mm-long PPLN crystal gave signal and idler ranges of 2.55 to 2.7 mum and 3.65 to 3.96 mum , respectively, limited by mirror reflectivity. A signal-tuning range of 40 nm was observed for 13.5 nm of pump tuning with a fixed grating period and temperature. The optical parameter oscillator could be operated at low temperature with no sign of photorefractive damage.

Observation of quadratic spatial solitons in periodically poled lithium niobate.

We report what are to our knowledge the first observation and characterization of quadratic spatial solitons in periodically poled lithium niobate (PPLN). Using a Nd:YAG (1064-nm) source, we observed self-trapped solitary-wave propagation over more than six diffraction lengths as a result of the cascaded quadratic nonlinear process. Low-threshold operation (5-kW peak power) was measured for the quasi-phase-matched PPLN structure designed for frequency doubling.

Efficient operation of a diode-bar-pumped Nd:YAG laser on the low-gain 1123-nm line.

Efficient operation of a Nd:YAG laser on the low-gain 1123-nm transition by end pumping with the reshaped output from a 7-W diode bar is reported. Using a simple standing-wave laser configuration and pumping with 5.6 W of incident power yielded a laser output power of 1.7 W in a near-diffraction-limited TEM00 mode with a beam quality factor of M2 < or approximately equal to 1.1. A unidirectional single-frequency ring laser was also constructed, yielding 180 mW of single-frequency output. The prospects for further increase in power by optimization of the resonator design are discussed.

Highly efficient second-harmonic and sum-frequency generation of nanosecond pulses in a cascaded erbium-doped fiber:periodically poled lithium niobate source.

By combining erbium-doped fiber sources based on a large mode-area design and periodically poled lithium niobate, we have obtained single-pass conversion efficiencies of as much as 83% (energy efficiency) for second-harmonic generation into the near IR (768 nm) and of 34% for sum-frequency generation into the green (512 nm) for nanosecond pulses, using first-order quasi-phase matching. Pulse energies in excess of 80microJ of second harmonic have been obtained from systems pumped by a single laser diode.

Generation of high-power blue light in periodically poled LiNbO(3).

We report the generation of 450-mW average blue (473-nm) power by frequency doubling of a diode-pumped 946-nm Nd:YAG laser. We achieved pulsed operation at a high repetition rate (~160kHz) by driving the relaxation oscillations of the laser. A 40% conversion efficiency to the second harmonic was obtained in a single-pass, extracavity, first-order, quasi-phase-matched process in which periodically poled lithium niobate (period 4.5microm , thickness 0.5mm , and length 15mm) at 140 degrees C was used. The resulting high-power blue beam was circular in profile and nearly diffraction limited, indicating that photorefractive effects do not appear to limit device performance.

Ring-doped cladding-pumped single-mode three-level fiber laser.

We propose and theoretically analyze three-level cladding-pumped fiber lasers in which the laser-active dopant is placed in a ring around a single-mode core. A ring-doped laser can work efficiently at wavelengths with strong small-signal absorption. This is otherwise difficult in a cladding-pumped fiber. Moreover, ring doping makes the laser less sensitive to quenching of the laser-active dopant and to excited-state absorption of the lasing field. In simulations of a Yb(3+) -doped fiber laser, ring doping increased the slope efficiency to 62%, up from 13% for a conventional core-doped fiber.

Optical parametric oscillation in periodically poled lithium niobate driven by a diode-pumped Q-switched erbium fiber laser.

We describe what is to our knowledge the first nanosecond periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO) driven by a fiber laser. The source was frequency doubled by a PPLN sample before pumping a second, 20-mm-long, PPLN crystal. The OPO threshold was <10muJ, with pump depletions of as much as 45% and a tunable signal range of 945-1450 nm (1690-4450-nm idler range). We demonstrated 130-nm signal tuning by varying the pump wavelength and doubling crystal's temperature. Also, we achieved 15-nm tuning with all crystals at a constant temperature. The results demonstrate the potential of the fiber laser:PPLN combination for practical, versatile, and tunable sources.

Diode-bar end-pumped high-power Nd:Y(3)Al(5)O(12) planar waveguide laser.

A compact high-power planar waveguide laser end pumped by a diode-bar is reported. The waveguide was fabricated by liquid-phase epitaxy and had an 80-microm-thick, 1.5-at. % Nd:Y(3)Al(5)O(12) core on a Y(3)Al(5)O(12) substrate. A maximum output power of 6.2 W was obtained at 1.064 microm when the device was pumped with a 20-W diode bar operating near 807 nm, giving an overall optical-to-optical conversion efficiency of 31%. The total device length was 5 cm.

High-power diode-bar end-pumped Nd:YLF laser at 1.053 microm.

We describe efficient cw operation of a Nd:YLF laser end pumped by two beam-shaped 20-W diode bars on the 1.053-microm transition. Fundamental transverse-mode operation with output power of 11.1 W for ~29.5 W of incident pump power was demonstrated. In Q-switched operation 8.4 W of average power at a pulse repetition frequency of 40 kHz and ~2.6-mJ pulse energy at a pulse repetition frequency of 1 kHz were achieved.