Efficient green generation by intracavity frequency doubling of an optically pumped semiconductor disk laser

We report the use of bismuth borate for efficient intracavity frequency doubling of an optically pumped semiconductor disk laser. An output power of 220 mW at 529 nm at room temperature has been demonstrated, corresponding to 52% conversion efficiency with respect to the fundamental power. The results are compared to frequency doubling with a potassium titanyl phosphate nonlinear crystal. PACS 42.55.Px; 42.70.Mp; 42.72.Bj     

Intracavity frequency doubling of a diode-pumped 946-nm Nd:YAG laser with bulk periodically poled MgO LiNbO(3)

We report what we believe is the first cw quasi-phase-matched intracavity frequency doubling of a diode-pumped 946-nm Nd:YAG laser by use of bulk periodically poled MgO-LiNbO(3). A maximum second-harmonic power of 5.9 mW was obtained at a laser diode power of 500 mW. The blue beam profile showed a TEM(00) single spatial mode of low ellipticity (1:1) because there was no walk-off problem. Bulk periodic domain inversion was accomplished by a corona discharge method with a first-order modulation period of 4.75 microm for a wavelength of 946 nm over a 2-mm interaction length in Z-cut 0.4-mm-thick MgO-LiNbO(3).     

Generation of ultraviolet (335-nm) light by intracavity frequency doubling from active mode-locking action of an external-cavity AlGaInP diode laser

An intracavity frequency-doubling scheme was merged with an actively mode-locked AlGaInP laser diode with an external cavity to provide efficient generation of 335-nm ultraviolet light. Intense pulses of <16ps were successfully generated inside the cavity at subgigahertz repetition frequencies. We applied those pulses to intracavity second-harmonic generation from a 5-mm-long LiIO(3) crystal, which resulted in average ultraviolet power of 70muW for an average fundamental power of 73 mW.     

Efficient resonant frequency doubling of a cw Nd:YAG laser in bulk periodically poled KTiOPO(4)

A cw Nd:YAG laser was quasi-phase-matched frequency doubled by a bulk periodically poled flux-grown KTiOPO(4) crystal in an external resonant cavity. The conversion efficiency and the second-harmonic power with a pump of 225 mW were 55% and 123.5 mW, respectively. The loss of the 1-cm-long crystal, which operated near room temperature, was 1.3% and was dominated by scatter from the cleaved facets of the crystal. No damage, photorefractive or other, was observed at intensites of 370Wmm(-2) , but beam size had to be optimized to eliminate thermal-induced instabilities in the doubling cavity.     

Blue 489-nm picosecond pulses generated by intracavity frequency doubling in a passively mode-locked optically pumped semiconductor disk laser

We report the generation of blue 489-nm picosecond laser pulses by intracavity second-harmonic generation in a mode-locked optically pumped InGaAs vertical-external-cavity surface-emitting laser. Mode locking achieved by a semiconductor saturable absorber mirror generated 5.8-ps-long sech²-shaped pulses at an emission wavelength of 978 nm and a repetition rate of 1.88 GHz. Intracavity frequency doubling in a 5-mm-long lithium triborate crystal generated blue picosecond pulses with a spectral width of 0.15 nm and an average output power of up to 6 mW.     

456-nm deep-blue laser generation by intracavity frequency doubling of Nd:GdVO4 under 879-nm diode pumping

We report on a simple, compact continuous-wave 456-nm laser by intracavity frequency doubling of an end-pumped Nd:GdVO₄ laser on the ⁴ F _3/2 → ⁴ I _9/2 transition. A 5-mm-long, 0.2-at % Nd:GdVO₄ bulk crystal is employed as the gain medium and the Nd³⁺ ion is directly pumped into the emitting level (⁴ F _3/2) by a novel 879-nm laser diode. Intracavity frequency doubling with a 15-mm-long LBO crystal and a 10-mm-long BiBO crystal in a linear cavity yield 56- and 118-mW single-ended blue outputs at the absorbed pump power of 11.9 W, respectively. The corresponding values are scaled to 286 and 391 mW, respectively, in a V-type cavity, with optical conversion efficiencies of 2.4 and 3.3% versus the absorbed pump power. The fluctuations of the 456-nm output power for both cases are less than 3% at the maximum output level.     

Efficient blue light generation by frequency doubling of a broad-area diode laser in a compact external cavity

An antireflection-coated broad-area laser diode is frequency stabilized in a compact unstable external cavity that was designed off-axis for transversal mode selection. The external cavity laser yielded up to 1 W near-diffraction-limited and tunable light centered around a wavelength of 970 nm. This light was frequency doubled by the use of periodically poled magnesium doped lithium niobate in a single-pass setup. With a 4-cm-long bulk crystal 57.5 mW of blue light could be generated out of 850 mW of infrared light resulting in a conversion efficiency of 6.7%. By using a 1.2-cm waveguide crystal it was possible to couple up to 64% of the infrared light into a 3.5 μm×5 μm channel and 142 mW of blue light at 488 nm could be obtained. An internal conversion efficiency of 44.1% and a wall-plug efficiency of 5.9% were achieved. Furthermore, the blue light was tunable over more than 5 nm. PACS 42.55.-f; 42.55.Px; 42.60.Da     

Efficient frequency doubling of a vertical-extended-cavity surface-emitting laser diode by use of a periodically poled KTP crystal

Blue light with a cw power in excess of 42 mW is generated from a frequency-doubled, extended-cavity InGaAs/GaAs 980-nm surface-emitting laser by use of a periodically poled KTP crystal.     

Tunable blue laser based on intracavity frequency doubling with a fan-structured periodically poled LiTaO(3) crystal

We introduce a new concept for a wavelength-tunable frequency-doubled laser diode with a single control parameter. The concept is based on intracavity frequency doubling in an external resonator geometry with spatial separation of the spectral components. The use of a fan-structured periodically poled LiTaO(3) crystal permits tuning of both the fundamental and the second harmonic simultaneously with one aperture. We demonstrate tunability over more than 10 nm in the blue (480.4 to 490.6 nm) with output powers of the order of 50 nW.     

Efficient generation of blue light by intracavity frequency doubling of a cw Nd:YAG laser with LBO

We report on the efficient room-temperature operation of ⁴F_3/2–⁴I_9/2 transition in a diode pumped Nd:YAG laser operating at 946 nm. An output power of 5.1 W and a slope efficiency of 23.6% at 946 nm have been obtained. Different LBO crystals of length 3×3×10 mm³, 3×3×15 mm³, 3×3×18 mm³ were selected as frequency doubling material for comparison. A maximum single-ended output power of 1.3 W at 473 nm was achieved by frequency doubling with an optical conversion efficiency of 5%. When the Nd:YAG rod was replaced by the one with high reflectivity coating at 473 nm on the pump side, the output power of blue light was almost twice that without high reflectivity coating for 473 nm at the same pump power level. Moreover, the theoretical optimum length of LBO crystal for intracavity frequency doubling was discussed, and the experimental results made a good agreement with it.     

High-efficiency blue generation by frequency doubling of femtosecond pulses in a thick nonlinear crystal

We have demonstrated highly efficient frequency doubling of femtosecond pulses in a thick, noncritically phase-matched KNbO(3) crystal under conditions of large group-velocity mismatch. At low power we observed a slope efficiency of ~300% nJ (-1) for harmonic conversion, and at higher powers we generated 170 mW of second-harmonic blue output for 300 mW of input light. Furthermore, we have shown that the focusing dependence for our conditions of large group-velocity mismatch is considerably different from that obtained for frequency doubling of continuous-wave light. We have also demonstrated that one can tune the spectral width of the generated blue light by varying the focusing conditions.     

120-nm,10-GHz supercontinuum generation in a dispersion-shifted fiber pumped by a three-stage compressed gain-switched DFB laser

The supercontinuum (SC) generation in conventional dispersion-shifted fiber (DSF) at the repetition rate of 10 GHz with a three-stage compressed gain-switched distributed feedback (DFB) laser as pump source was demonstrated. A novel SC pulse source with a bandwidth up to 120 nm was obtained. At the same time, the stable, narrow pulses with pulsewidth of 9.2 ps and time-bandwidth product of 0.46 were filtered out across the whole SC bandwidth.     

Efficient frequency doubling of a pulsed laser diode by use of a periodically poled KTP waveguide crystal with Bragg gratings

Blue light with an average power of as much as 7.5 mW in picosecond pulses has been generated at 486, 488, and 491 nm from a frequency-doubled, nonresonant injection seeded, gain-switched InGaAs/GaAs diode laser by use of a periodically poled KTP waveguide crystal that incorporates a Bragg grating section.     

Intracavity generation of second harmonics and sum frequences in LiIO3 crystal in an infrared He-Ne laser

Several second harmonics and sum frequencies were generated in a phase-matched LiIO₃ crystal placed within an optical cavity of a high-power He-Ne infrared laser operated at 1.15m.     

Violet light generation by frequency doubling of GaAlAs diode laser using a metallo-organic complex crystal ZnCd(SCN)4

Violet 404-nm radiation is generated by type-I single-pass frequency doubling of the output of an GaAlAs diode laser in critically phase-matched ZnCd(SCN)₄ (ZCTC) crystal, a metallo-organic complex crystal. In this paper, its refractive index and second-harmonic generation phase-matching angles are reported. Using a 3-mm-long ZCTC crystal, a diode laser power of 473 mW generated 390 μW of second-harmonic radiation. More recently, 380-nm, 20 μW ultraviolet (UV) radiation is also realized by frequency doubling of the 100 mW output of a continuous-wave Ti:sapphire laser at 760 nm. ZCTC is a promising UV nonlinear optical candidate material for frequency doubling of diode lasers.     

Yellow light generation by frequency doubling of a diode-pumped Nd:YAG laser

We demonstrate the generation of TEM₀₀ mode yellow light in critically type II phase-matched KTiOPO₄ (KTP) with intracavity frequency doubling of a diode-pumped Nd:YAG laser at room temperature. After a 150 μm thick etalon have been inserted into the cavity, the stability and beam quality of the second harmonic generation (SHG) is enhanced. A continuous wave (CW) TEM₀₀ mode output power of 1.67 W at 556 nm is obtained at a pump level of 16 W. The total optical to optical conversion efficiency is about 10.44%. To the best of our knowledge, this is the first Watt-level yellow light generation by frequency doubling of Nd:YAG laser.     

Efficient quasi-phase-matched frequency doubling with phase compensation by a wedged crystal in a standing-wave external cavity

In standing-wave enhancement cavities for frequency doubling, second-harmonic fields are generated in both directions of propagation. To add the fields coherently, one should compensate for the phase shifts introduced by dispersive elements in the cavity. We experimentally demonstrate phase compensation in a compact standing-wave frequency-doubling cavity by use of a wedged periodically poled KTP crystal. The highest conversion efficiency and second-harmonic power obtained by pumping with a 1064-nm cw Nd:YAG laser were 69.4% and 268 mW, respectively.     

Ultraviolet generation by first-order frequency doubling in periodically poled KTiOPO(4)

First-order quasi-phase-matched frequency doubling at 780 nm in a 1-mm-thick periodically poled KTiOPO(4) crystal with an inverted-domain period of 2.95 microm has been demonstrated for the first time to the authors' knowledge. A normalized conversion efficiency of 1.1%W(-1) cm(-1) has been obtained in cw mode. Experiments show that group-velocity walk-off prevents efficient frequency doubling of femtosecond pulses in KTiOPO(4) in the UV spectral range. However, because of the large optical nonlinearity, periodically poled structures can be efficiently used for frequency doubling of cw and pulsed lasers with pulse lengths as short as ~1 ps .     

Room-temperature, continuous-wave 1-W green power by single-pass frequency doubling in a bulk periodically poled MgO:LiNbO3 crystal

Continuous-wave high-power green light generation at room temperature is reported in a single-pass frequency-doubling configuration with bulk periodically poled MgO:LiNbO3 crystal placed outside a diode end-pumped Nd:GdVO4 laser. The MgO:LiNbO3 samples of 6.95-microm domain period, uniform periodicity, and 50% duty cycle along the entire crystal length are fabricated by use of a high-voltage multipulse poling method. A maximum power of 1.18 W at 531 nm with 16.8% conversion efficiency is obtained from a 2-mm-thick, 25-mm-long MgO:LiNbO3 crystal; the corresponding internal green power and conversion efficiency are 1.38 W and 19.6%, respectively, whereas the normalized conversion efficiency is 3.3%/W.     

An all-solid-state tunable 214.5-nm continuous-wave light source by using two-stage frequency doubling of a diode laser

3 and β-BaB₂O₄ crystals. The power of the generated 214.5-nm light amounts to more than 100 μW. This light source will be used for laser cooling of Cd⁺ ions. Received: 4 August 1997/Revised version: 28 October 1997