250 mW of coherent blue 460-nm light generated by single-pass frequency doubling of the output of a mode-locked high-power diode laser in periodically poled KTP.

We report on the generation of 250mW of coherent 460-nm light by single-pass frequency doubling of the mode-locked picosecond pulses emitted by an InGaAs diode master oscillator power amplifier in periodically poled KTP.

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.

Wavelength tuning and spectral properties of distributed feedback diode lasers with a short external optical cavity.

We report on the wavelength tuning and spectral properties of distributed feedback (DFB) diode lasers operated with a plane external cavity (XC) mirror positioned as close as possible to the diode-laser front facet. These lasers generate single-frequency near IR radiation at wavelengths of 1392, 1580, 1602, and 1653 nm. A piezoelectric variation of the XC length provided continuous single-frequency tuning to as high as 19 GHz. A further benefit of XC DFB lasers is a residual amplitude modulation per gigahertz tuning of less than 10(-3). The XC feedback also suppresses residual side-mode oscillations to less than 60 dB. The laser's total intensity noise is close to the shot noise limit. The laser linewidth (measured in a beat note experiment) is less than 90 kHz within an acquisition time of 40 ms. The advantageous properties of XC DFB lasers for molecular spectroscopy are demonstrated by recording R(3) 2nu(3) overtone spectra of methane by single-scan single-pass absorption or frequency-modulation spectroscopy.

Origin of magnetic field enhancement in the generation of terahertz radiation from semiconductor surfaces.

We present a theory of the magnetic field enhancement of terahertz (THz) emission from photogenerated carriers in the surface depletion region of a semiconductor. A combination of the Drude-Lorentz model for the carrier dynamics with an appropriate solution of the radiation problem is sufficient to explain the strong B -field enhancement in THz radiation that has been observed experimentally. The effect arises primarily from the increased radiation efficiency of transient currents flowing in the plane of the surface. The model provides quantitative agreement with experiment for the pronounced angular dependence of the enhancement and predicts the correct trend for the enhancement in a variety of materials.

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.

Diode-pumped singly resonant continuous-wave optical parametric oscillator with wide continuous tuning of the near-infrared idler wave.

We demonstrate wide, continuous tuning of the single-frequency idler wave of a cw singly resonant optical parametric oscillator (SRO). The SRO consists of a periodically poled LiNbO(3) crystal for quasi-phase matching in a four-mirror signal-resonant ring cavity. The SRO, excited by 2.25 W of 924-nm radiation from an InGaAs diode laser, generates as much as 200 mW of single-frequency 2.1-mum idler radiation. We tune the idler frequency continuously within a range as large as 56 GHz by changing the wavelength of the diode pump laser. The versatility of this continuously tunable single-frequency infrared source is demonstrated by recording of N(2)O rovibrational absorption lines near 2.1 mum.

2.5-GHz repetition-rate singly resonant optical parametric oscillator synchronously pumped by a mode-locked diode oscillator amplifier system.

We report on an optical parametric oscillator (OPO) that is synchronously pumped directly by a diode laser. This laser is an actively mode-locked master-oscillator power-amplifier system that produces 20-ps pulses at 927 nm with a repetition rate of 2.5 GHz and an average power of 0.9 W. The OPO, which is a singly resonant device based on periodically poled lithium niobate, generates 7.8-ps pulses. The OPO threshold is 300 mW of average pump power, and the maximum average idler output power is 78 mW at a wavelength of 2100 nm. By changing the crystal temperature we can wavelength tune the output in the ranges 1530-1737 nm (signal) and 1986-2348 nm (idler). Rapid wavelength tuning of the OPO over 46 nm (signal) and 74 nm (idler) is achieved through tuning the cavity length over 28 microm by use of a piezoelectric transducer.

Nanosecond optical parametric oscillator based on large-aperture periodically poled RbTiOAsO(4).

We report on optical parametric oscillators (OPO's) based on periodically poled RbTiOAsO(4) (PP RTA), which are pumped by Q -switched solid-state lasers. With a diode-pumped Nd:YVO(4) laser (pulse energy, 800microJ ; pulse duration, 5.5 ns; repetition rate, 1 kHz) the PP RTA OPO generated 1.58-microm signal and 3.26-microm idler radiation with a signal pulse energy of 45microJ . The large aperture of 3 mmx3 mm of the PP RTA crystal also permitted OPO operation with pump pulse energies as high as 65 mJ, provided by a flash-lamp-pumped Q -switched Nd:YAG laser (pulse duration, 20 ns; repetition rate, 10 Hz). With this pump source the OPO generated signal pulse energies as high as 17 mJ, corresponding to an efficiency of 26%. The performance of this OPO shows that large-aperture PP RTA crystals are well suited for pulsed nanosecond OPO operation with pump pulse energies of tens of millijoules.

1 W of blue 465-nm radiation generated by frequency doubling of the output of a high-power diode laser in critically phase-matched LiB3O5.

Blue 465-nm radiation is generated by frequency doubling of the output of an InGaAs diode-laser oscillator-amplifier system in critically phase-matched LiB(3)O(5) (LBO). The diode-laser system emitted 4 W of single-frequency 930-nm radiation in a near-diffraction-limited beam (M(2)<1.2) . The laser power is enhanced to values of up to 150 W in a resonant external ring cavity. The LBO crystal is placed at a resonator internal focus. The frequency doubling in the LBO crystal generates blue radiation at 465 nm with a power of 1 W. The spectral width of the blue radiation is less than 3 MHz, and the value of the M(2) beam parameter is less than 1.2.

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.

Continuous-wave quasi-phase-matched generation of 60 mW at 465 nm by single-pass frequency doubling of a laser diode in backswitch-poled lithium niobate.

We report continuous-wave single-pass second-harmonic generation (SHG) in 4-mum -period 0.5-mm-thick backswitch-poled lithium niobate. Pump sources at 920-930 nm include both Ti:sapphire and diode-oscillator-amplifier lasers. SHG of a Ti:sapphire laser at 6.1%/W efficiency, producing 61 mW of power at 460 nm, is demonstrated in 50-mm-long periodically poled lithium niobate samples with a nonlinear coefficient d(eff) approximately 9pm/V, and 60 mW at 465 nm and 2.8%/W efficiency is obtained by SHG of a laser-diode source.

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.

Frequency-stable operation of a diode-pumped continuous-wave RbTiOAsO(4) optical parametric oscillator.

Frequency-stable operation of a diode-pumped continuous-wave optical parametric oscillator (OPO) of RbTiOAsO(4) is demonstrated. Piezoelectric and fast electro-optic control of the optical length of the two-mirror OPO cavity (resonant for the pump and the idler waves) compensates for thermal changes in the refractive index of the OPO crystal (induced by absorption of pump light) and acoustic perturbations of the cavity length. Pumped by 405mW of the 810-nm output of a GaAlAs masterf-oscillator-tapered-amplifier diode laser system, the OPO generates a power-stable single-frequency signal wave at 1.24microm with an output of 84mW and a spectral bandwidth of less than 10MHz.

Single-mode continuous-wave Cr(3+):LiSAF ring laser pumped by an injection-locked 670-nm broad-area diode laser.

We report on an efficient continuous-wave Cr(3+):LiSrAlF(6) ring laser pumped by the near-diffraction-limited output of an injection-locked 665-nm broad-area diode laser. With an absorbed pump power of 120 mW the ring laser generates 22 mW of single-mode 855-nm radiation with a spectral linewidth of less than 10 MHz. Unidirectional operation and longitudinal-mode control of this ring laser is achieved by injection of 855-nm diode-laser radiation into the ring cavity. Optical feedback of ring-laser radiation into the diode laser narrows the diode laser's linewidth and locks its frequency to a resonance of the ring resonator.

Coherent 70.9-nm radiation generated in neon by frequency tripling the fifth harmonic of a Nd:YAG laser.

We have produced coherent radiation in the XUV region at 70.9 nm by frequency tripling the fifth harmonic of Nd:YAG laser radiation in neon. BaB(2)O(4) was used to generate the fifth harmonic at 212.8 nm with an output pulse energy of 20 mJ and a pulse width of 5 nsec. Subsequent frequency tripling in neon gas generated 10 W of peak power at 70.9 nm.