Wide wavelength tuning of an optical parametric oscillator through electro-optic shaping of the gain spectrum.

We present a novel technique for tuning an optical parametric oscillator (OPO) through electro-optically induced shape variations of the parametric gain spectrum in quasi-phase-matched lithium niobate (LN). The diode-pumped, triply resonant continuous-wave OPO is based on a 58-mm-long LN crystal that consists of three equally long sections, the outer sections being periodically poled with a 50% duty cycle. The center section is single-domain material and serves as a tunable phase shifter through the electro-optic effect. By application of a voltage of up to 1230 V, the OPO signal and idler wavelengths are tuned over 102 nm from 1560 to 1660 nm, in good agreement with theory.

Generation of sub-6-fs blue pulses by frequency doubling with quasi-phase-matching gratings.

We demonstrate the generation of sub-6-fs pulses centered at 405 nm by frequency doubling of 8.6-fs Ti:sapphire laser pulses. The frequency doubling is carried out in a nonlinearly chirped quasi-phase-matching grating fabricated in a lithium tantalate substrate. This device simultaneously provides frequency conversion and pulse compression of the positively prechirped fundamental pulses. The second-harmonic pulses are characterized in a cross-correlation setup, and their pulse shapes are retrieved by two iterative phase-reconstruction algorithms. The generated second-harmonic spectrum spans a bandwidth of 220 THz. To our knowledge, these are the shortest pulses ever generated in the blue spectral region.

Tuning characteristics of narrowband THz radiation generated via optical rectification in periodically poled lithium niobate.

The tuning properties of pulsed narrowband THz radiation generated via optical rectification in periodically poled lithium niobate have been investigated. Using a disk-shaped periodically poled crystal tuning was easily accomplished by rotating the crystal around its axis and observing the generated THz radiation in forward direction. In this way no beam deflection during tuning was observed. The total tuning range extended from 180 GHz up to 830 GHz and was limited by the poling period of 127 microm which determines the maximum THz frequency in forward direction.

Efficient second-harmonic generation at 384 nm in periodically poled lithium tantalate by use of a visible Yb--Er-seeded fiber source.

We generated 56 mW of average power at 384 nm in periodically poled lithium tantalate by use of a visible fiber source based on a variable-pulse format seeded Yb-Er amplifier and frequency upconversion in periodically poled KTP. The feasibility of high-average-power, wide ultraviolet wavelength-range fiber-based sources is evaluated.

Singly resonant continuous-wave optical parametric oscillator pumped by a diode laser.

We report on what is believed to be the first singly resonant cw optical parametric oscillator (SRO) that is directly pumped by a diode laser. The SRO consists of a 38-mm-long periodically poled LiNbO(3) crystal in a four-mirror signal-resonant ring cavity. Pumped by 2.5 W of 925-nm diode-laser radiation, the SRO generates 480 mW of single-frequency idler radiation at 2.1mum . The wavelengths of the signal and the idler output are tuned in the ranges of 1.55 to 1.70mum and 2.03 to 2.29mum, respectively, by tuning the wavelength of the diode laser from 924.0 to 925.4 nm.

Periodically poled potassium niobate for second-harmonic generation at 463 nm.

We report on the fabrication and characterization of quasi-phase-matched potassium niobate crystals for second-harmonic generation. Periodic 30-mum -pitch antiparallel ferroelectric domains are fabricated by means of poling in an electrical field. Both birefrigence and periodic phase shift of the generated second harmonic contribute to phase matching when the d(31) nonlinear optical tensor element is used. 3.8 mW of second-harmonic radiation at 463 nm is generated by frequency doubling of the output of master-oscillator power-amplifier diode laser in a 5-mm-long crystal. The measured effective nonlinear coefficient is 3.7pm/V. The measured spectral acceptance bandwidth of 0.25 nm corresponds to the theoretical value.

Single-frequency continuous-wave radiation from 0.77 to 1.73 microm generated by a green-pumped optical parametric oscillator with periodically poled LiTaO3.

We describe a cw optical parametric oscillator (OPO) with multigrating periodically poled LiTaO(3) . Pumped by a single-frequency 532-nm laser, the OPO emits single-frequency radiation at wavelengths from 0.77 to 1.73 microm with as much as 60 mW of output power. Mode-hop-free operation for as long as 50 min, a low frequency drift (<70 MHz/h), and as much as 700-MHz continuous frequency tuning of signal and idler are demonstrated.

Nanosecond periodically poled lithium niobate optical parametric generator pumped at 532 nm by a single-frequency passively Q-switched Nd:YAG laser.

We report an efficient, visible, nanosecond optical parametric generator of periodically poled lithium niobate pumped at 532 nm by a frequency-doubled, diode-pumped, passively Q -switched, single-mode Nd:YAG laser with 90-muJ pulse energy. The signal radiation is tunable from 637 to 593 nm. The maximum signal-conversion efficiency is 23%. Optical parametric amplification of a He-Ne laser at 632.8 nm is also studied.

Self-injection-locking of a CW-OPO by intracavity frequency-doubling the idler wave.

We report on the observation of self-injection-locking of the signal wave of an optical parametric oscillator (OPO) with the intracavity frequency doubled idler wave. The two-mirror OPO is based on a periodically poled LiNbO3 (PPLN) crystal and pumped with a grating stabilized, continuous-wave (CW) single-frequency diode master-oscillator power-amplifier (MOPA) system. Simultaneous quasi-phase-matching (QPM) of OPO and second harmonic generation (SHG) is provided in the same crystal which carries two different domain gratings. The beat of the signal wave and the frequency-doubled idler wave is suppressed within a 500-kHz wide frequency range centered around zero as expected for self-injection- locking. The measurements prove the feasibility of optically phase-stabilized by-three-division of an optical frequency with CW-OPOs using cascaded nonlinearities.

Diode-pumped continuous-wave widely tunable optical parametric oscillator based on periodically poled lithium tantalate.

We report on a diode-laser pumped cw optical parametric oscillator (OPO) based on quasi-phase-matched periodically poled lithium tantalate. Pumped by the 2.3-W single-frequency, nearly diffraction-limited 925-nm output of an InGaAs diode master-oscillator power amplifier, the pump and signal resonant OPO generates a single-frequency idler wave with an output of as much as 244 mW. The wavelengths of the signal and idler waves are widely tunable in the range 1.55-2.3mum by use of different poling periods (27.3 to 27.9mum) and by variation of the crystal temperature in the range 70-190 degrees C.

Tunable ultraviolet radiation by second-harmonic generation in periodically poled lithium tantalate.

We describe electric-field poling of fine-pitch ferroelectric domain gratings in lithium tantalate and characterization of nonlinear-optical properties by single-pass quasi-phase-matched second-harmonic generation (QPM SHG). With a 7.5-microm-period grating, the observed effective nonlinear coefficient for first-order QPM SHG of 532-nm radiation is 9 pm/V, whereas for a grating with a 2.625-microm period, 2.6 pm/V was observed for second-order QPM SHG of 325-nm radiation. These values are 100% and 55% of the theoretically expected values, respectively. We derive a temperature-dependent Sellmeier equation for lithium tantalate that is valid deeper into the UV than currently available results, based on temperature-tuning experiments at different QPM grating periods combined with refractive-index data in the literature.

Passively Q-switched 180-ps Nd:LaSc(3)(BO(3))(4) microchip laser.

We passively Q switched a Nd:LaSc(3)(BO(3))(4) microchip laser with an antiresonant Fabry-Perot saturable absorber (A-FPSA) and achieved single-frequency, 180-ps pulses with 0.1 microJ of pulse energy at a repetition rate of 110 kHz. Because of the compactness and scaling possibilities offered by the A-FPSA, the pulse width can be varied from 180 ps to 30 ns and the repetition rate from 50 kHz to 7 MHz.

Intracavity frequency doubling of a continuous-wave, diode-laser-pumped neodymium lanthanum scandium borate laser.

Neodymium-doped lanthanum scandium borate [Nd:LaSc(3)(BO(3))(4)] is a new material for efficient and compact diode-pumped solid-state lasers. A simple plane-plane 3-mm-long resonator is formed by a coated Nd(10%):LaSc(3)(BO(3))(4) crystal and a coated potassium titanyl phosphate (KTP) crystal. The second-harmonic output power at 531 nm is 522 mW at 2.05-W incident pump power of the diode laser. The corresponding optical efficiency is 25%, and the conversion efficiency from the fundamental to the second harmonic is 55%. The wellknown chaotic power fluctuations of intracavity frequency-doubled lasers (green problem) are avoided by use of a short KTP crystal, between 0.5 and 2 mm in length.