Frequency doubling with KNbO(3) in an external cavity

Monolithic Saturable Absorber with Gallium Arsenide Nanowires Integrated on the Flexible Substrate for Optical Pulse Generation

In this work, we demonstrated a kind of flexibly monolithic saturable absorber (SA) with GaAs nanowires (NWs) on polyimide (PI) plastic substrate for broadband optical modulation at 1.0 and 1.5 µm, separately. The monolithic SA sample was prepared by the metalorganic vapor phase epitaxy (MOVPE) method. The crystal structure and element analysis were examined carefully by high-resolution scanning transmission electron microscopy (HRSTEM) and energy-dispersive X-ray spectroscopy (EDX). We observed a high-density distribution of NWs on the flexible substrate by scanning electron microscopy (SEM). In addition, linear and nonlinear optical properties of the sample were examined by testing the photoluminescence and absorption properties, which showed its potential application as an optical switch due to the pure semiconducting properties. After the characterizations, we experimentally demonstrated this monolithic SA for laser modulation at 1.0 and 1.5 µm, which yielded the minimum optical pulse widths of 1.531 and 6.232 µs, respectively. Our work demonstrated such a kind of monolithic flexible NW substrate-integrated device used for broadband optical modulation, which not only eased the integration process of NWs onto the fiber endface, but also proved the potential of easily integrating with more semiconducting nanomaterials (e.g., graphene, MoS2, …) to realize monolithic active flexible photonic systems, such as a microscale phase modulator, delay-line, and so on, paving an easy avenue for the development of both active and flexible photonic devices.

High-power, frequency-quadrupled UV laser source resonant with the 1S0-3P1 narrow intercombination transition of cadmium at 326.2 nm

We present a novel high-power, frequency-stabilized UV laser source at 326.2 nm, resonant with the Cd ¹S₀-³P₁ narrow intercombination transition. We achieve a maximum produced power of 1 W at 326.2 nm by two successive frequency doubling stages of a narrow-linewidth (<1 kHz) seed laser at 1304.8 nm. Approximately 3.4 W of optical power at 652.4 nm is produced by a visible Raman fiber amplifier (VRFA) that amplifies and generates the second harmonic of the infrared radiation. The visible light is subsequently frequency-doubled down to 326.2 nm in a nonlinear bow-tie cavity using a Brewster-cut beta-barium-borate (BBO) crystal, with a maximum conversion efficiency of approximately 40% for 2.5 W of coupled red power. Full characterization of the laser source, together with spectroscopy signals of all Cd isotopes, spanning more than 4 GHz in the UV, are shown.

High power continuous laser at 461 nm based on a compact and high-efficiency frequency-doubling linear cavity

A Watt-level continuous and single frequency blue laser at 461 nm is obtained by frequency-doubling an amplified diode laser operating at 922 nm via a LBO crystal in a resonant Fabry-Pérot cavity. We achieved a best optical conversion efficiency equal to 87% with more than 1 W output power in the blue, and limited by the available input power. The frequency-converted beam is characterized in terms of long term power stability, residual intensity noise, and geometrical shape. The blue beam has a linewidth of the order of 1 MHz, and we used it to magneto-optically trap ⁸⁸Sr atoms on the 5s^2 1S₀ - 5s5p ¹P₁ transition. The low-finesse, linear-cavity doubling system is very robust, maintains the lock for several days, and is compatible with a tenfold increase of the power levels which could be obtained with fully-fibered amplifiers and large mode area fibers.

Cavity-enhanced sum-frequency generation of blue light with near-unity conversion efficiency

We report on double-resonant highly efficient sum-frequency generation in the blue range. The system consists of a 10-mm-long periodically poled KTP crystal placed in a double-resonant bow-tie cavity and pumped by a fiber laser at 1064.5 nm and a Ti:sapphire laser at 849.2 nm. An optical power of 375 mW at 472.4 nm in a TEM₀₀ mode was generated with pump powers of 250 mW at 849.2 nm and 200 mW at 1064.5 nm coupled into the double-resonant ring resonator with 88% mode-matching. The resulting internal conversion efficiency of 95(±3)% of the photons mode-matched to the cavity constitutes, to the best of our knowledge, the highest overall achieved quantum conversion efficiency using continuous-wave pumping. Very high conversion efficiency is rendered possible due to very low intracavity loss on the level of 0.3% and high nonlinear conversion coefficient up to 0.045(0.015) W^-1. Power stability measurements performed over one hour show a stability of 0.8%. The generated blue light can be tuned within 5 nm around the center wavelength of 472.4 nm, limited by the phase-matching of our nonlinear crystal. This can however be expanded to cover the entire blue spectrum (420 nm to 510 nm) by proper choice of nonlinear crystals and pump lasers. Our experimental results agree very well with analytical and numerical simulations taking into account cavity impedance matching and depletion of the pump fields.

Realizing a high-efficiency 426nm laser with PPKTP by reducing mode-mismatch caused by the thermal effect

We report on a high conversion efficiency tunable laser at 426 nm by adopting an external frequency-doubling cavity pumped by a diode laser. For the frequency-doubling process at 426 nm, the major challenge of increasing the conversion efficiency is mode-match degradation originating from the severely thermal effect. Here, we find that the center of the equivalently thermal lens is not at the center of the nonlinear crystal. We minimize the variation of beam parameters of the Gaussian beam in the external cavity by optimizing the center of the thermal lens to beam waist. As a result, the mode-match degradation is reduced as the incident power is increased. Finally, a 405 mW blue light is obtained with the conversion efficiency of 81%.

Highly coherent, watt-level deep-UV radiation via a frequency-quadrupled Yb-fiber laser system

We demonstrate a 1.4 W continuous-wave (CW) laser at 243.1 nm. The radiation is generated through frequency quadrupling the output of a ytterbium-doped fiber amplifier system. which produces >10  W of CW power at 972.5 nm. We demonstrate absolute frequency control by locking the laser to an optical frequency comb and exciting the 1S-2S transition in atomic hydrogen. This frequency-stabilized, high-power deep-UV laser is of significant interest for precision spectroscopy of simple and exotic atoms, two-photon laser cooling of hydrogen, and Raman spectroscopy.

A highly stable monolithic enhancement cavity for second harmonic generation in the ultraviolet

We present a highly stable bow-tie power enhancement cavity for critical second harmonic generation (SHG) into the UV using a Brewster-cut β-BaB₂O₄ (BBO) nonlinear crystal. The cavity geometry is suitable for all UV wavelengths reachable with BBO and can be modified to accommodate anti-reflection coated crystals, extending its applicability to the entire wavelength range accessible with non-linear frequency conversion. The cavity is length-stabilized using a fast general purpose digital PI controller based on the open source STEMlab 125-14 (formerly Red Pitaya) system acting on a mirror mounted on a fast piezo actuator. We observe 130 h uninterrupted operation without decay in output power at 313 nm. The robustness of the system has been confirmed by exposing it to accelerations of up to 1 g with less than 10% in-lock output power variations. Furthermore, the cavity can withstand 30 min of acceleration exposure at a level of 3 g_rms without substantial change in the SHG output power, demonstrating that the design is suitable for transportable setups.

High-power continuous-wave narrow-linewidth 253.7 nm deep-ultraviolet laser

A 760 mW stable continuous-wave narrow-linewidth 253.7 nm deep-ultraviolet laser is developed for laser cooling of mercury atoms. It is based on a high-power 1014.8 nm room-temperature fiber laser amplifier and two cascaded efficient frequency-doubling stages. The saturated absorption spectrum of Hg202 on the 6S₀1-6P₁3 transition is demonstrated with a high signal-to-noise ratio. This deep-ultraviolet laser has significant applications in quantum optics and laser cooling of mercury atoms in 2D and 3D magneto-optical traps.

Generation of high-power single-frequency 397.5 nm laser with long lifetime and perfect beam quality in an external enhancement-cavity with MgO-doped PPSLT

Continuous-wave single-frequency high power 397.5 nm laser with long lifetime and perfect beam quality is one of the essential resource to generate the squeezed and entanglement states of optical beams resonant with D₁ line of Rubidium atoms at 795 nm. In this paper, We present the experimental generation of single-frequency high power 397.5 nm ultra-violet (UV) laser with long lifetime and perfect beam quality by using periodically poled MgO-doped stoichiometric lithium tantalate (MgO:PPSLT) crystal as the frequency doubler in an external enhancement ring cavity. When the transmission of the input coupler is 5.5%, the maximal output power of single-frequency 397.5 nm UV laser of 407 mW is obtained under the incident pump power of 1.9 W with the corresponding conversion efficiency of 22.8%. When the output power is 290 mW, the measured power stability and the beam quality are lower than 0.28% and 1.02, respectively. Moreover, any damage is not observed in our experiment which lasts about 1 year.

Cavity-enhanced frequency doubling from 795nm to 397.5nm ultra-violet coherent radiation with PPKTP crystals in the low pump power regime

We demonstrate a simple, compact and cost-efficient diode laser pumped frequency doubling system at 795 nm in the low power regime. In two configurations, a bow-tie four-mirror ring enhancement cavity with a PPKTP crystal inside and a semi-monolithic PPKTP enhancement cavity, we obtain 397.5nm ultra-violet coherent radiation of 35mW and 47mW respectively with a mode-matched fundamental power of about 110mW, corresponding to a conversion efficiency of 32% and 41%. The low loss semi-monolithic cavity leads to the better results. The constructed ultra-violet coherent radiation has good power stability and beam quality, and the system has huge potential in quantum optics and cold atom physics.

Highly efficient second harmonic generation of a light carrying orbital angular momentum in an external cavity

Traditional methods for generating a light carrying orbital angular momentum (OAM) include the use of holographic diffraction gratings, vortex phase plates and spatial light modulators. Here we report a new method for highly efficient second-harmonic generation (SHG) of a light with OAM. By properly aligning an external cavity that contains a quasi-phase matching nonlinear crystal and pumping it with a light carrying OAM, mode matching between the pump light and the cavity's higher order Laguerre-Gaussian (LG) mode is achieved, SHG with a conversion efficiency of up to 10.3% is obtained. We have demonstrated for the first time that the cavity can stably operate at its higher order LG mode similar to that of a Gaussian mode. The second harmonic generated light has an OAM value that is double with respected to the OAM value of the pump light. The parameters that affect the beam quality and conversion efficiency are discussed in detail. Our work opens a brand new field in laser optics and makes the first step toward high efficiency processing using a light carrying OAM.

Efficient frequency doubling at 399 nm

We describe a reliable, high-power, and narrow-linewidth laser source at 399 nm, which is useful for cooling and trapping of ytterbium atoms. A continuous-wave titanium-sapphire laser at 798 nm is frequency doubled using a lithium triborate crystal in an enhancement cavity. Up to 1.0 W of light at 399 nm has been obtained from 1.3 W of infrared light, with an efficiency of 80%.

Observation of two-photon fluorescence for Rhodamine 6G in microbubble resonators

We report an observation of multi-photon excitation of organic chromophores in microbubble whispering gallery mode resonators. High-Q microbubble resonators were formed by heating a pressurized fused silica capillary to form a hollow bubble that was then filled with liquid. In this work, the microbubble was filled with a solution of Rhodamine 6G dye. The resonator and dye were excited by evanescently coupling continuous wave (CW) light from a 980 nm laser diode using a tapered optical fiber. The two-photon fluorescence of the dye can be seen with pump powers as low as 700 μW.

Generation of blue light at 426 nm by frequency doubling with a monolithic periodically poled KTiOPO4

Continuous-wave (cw) blue laser generation at 426 nm by frequency doubling with a monolithic periodically poled KTP (PPKTP) cavity is reported in this paper. Without any free mirrors, the standing-wave cavity solely consists of a monolithic PPKTP crystal, and both ends of which are spherically polished and mirror-coated. An output power of 158 mW is obtained when the pump power is 350 mW. The conversion efficiency is 45%. The dependence of the conversion efficiency on the temperature and the incident fundamental power has been discussed. Such a system is integrally stable and compact for long-time operation under temperature control. The system is much more stable than the usual servo lock system for external cavity doubling.

A simplified 461-nm laser system using blue laser diodes and a hollow cathode lamp for laser cooling of Sr

We develop a simplified light source at 461 nm for laser cooling of Sr without frequency-doubling crystals but with blue laser diodes. An anti-reflection coated blue laser diode in an external cavity (Littrow) configuration provides an output power of 40 mW at 461 nm. Another blue laser diode is used to amplify the laser power up to 110 mW by injection locking. For frequency stabilization, we demonstrate modulation-free polarization spectroscopy of Sr in a hollow cathode lamp. The simplification of the laser system achieved in this work is of great importance for the construction of transportable optical lattice clocks.

Pump-tunable continuous-wave singly resonant optical parametric oscillator from 2.5 to 4.4 microm

We report a continuous-wave singly resonant optical parametric oscillator pumped by a widely tunable titanium-doped sapphire ring laser. It produces up to 0.8 W of mid-infrared power. The wavelength can be tuned in a few seconds from 2.5 to 3.5 microm or from 3.4 to 4.4 microm and scanned up to 40 GHz without mode-hops by only changing the pump beam wavelength. Spectroscopic capability is demonstrated by measuring parts of the photoacoustic absorption spectrum of NH(3) near 3196 cm(-1).

Generation of quasi-continuous-wave vacuum-ultraviolet coherent light by fourth-harmonic of a Ti:sapphire laser with KBBF crystal

We report the generation of quasi-continuous-wave vacuum-ultraviolet (VUV) coherent light based on a Ti:sapphire laser with two successive frequency doubling stages. In the first stage, UV light at 399 nm with power of 1.1 W was obtained by exploiting an enhanced cavity. With a KBBF crystal as nonlinear material, quasi-continuous-wave VUV coherent light with power of about 25 mW at 199.5 nm and 4.7 mW at 193.5 nm were achieved through a single-pass SHG configuration, respectively, in the second stage.

750 mW continuous-wave solid-state deep ultraviolet laser source at the 253.7 nm transition in mercury

A high-power continuous-wave coherent light source at 253.7 nm is described. It is based on a solid-state Yb:YAG disk laser with two successive frequency doubling stages and is capable of generating stable output powers of up to 750 mW. Spectroscopy of the 6 (1)S(0)-6 (3)P(1) transition of mercury has been demonstrated.

A frequency comb in the extreme ultraviolet

Since 1998, the interaction of precision spectroscopy and ultrafast laser science has led to several notable accomplishments. Femtosecond laser optical frequency 'combs' (evenly spaced spectral lines) have revolutionized the measurement of optical frequencies and enabled optical atomic clocks. The same comb techniques have been used to control the waveform of ultrafast laser pulses, which permitted the generation of single attosecond pulses, and have been used in a recently demonstrated 'oscilloscope' for light waves. Here we demonstrate intra-cavity high harmonic generation in the extreme ultraviolet, which promises to lead to another joint frontier of precision spectroscopy and ultrafast science. We have generated coherent extreme ultraviolet radiation at a repetition frequency of more than 100 MHz, a 1,000-fold improvement over previous experiments. At such a repetition rate, the mode spacing of the frequency comb, which is expected to survive the high harmonic generation process, is large enough for high resolution spectroscopy. Additionally, there may be many other applications of such a quasi-continuous compact and coherent extreme ultraviolet source, including extreme ultraviolet holography, microscopy, nanolithography and X-ray atomic clocks.

Detailed study of an efficient blue laser source by second-harmonic generation in a semimonolithic cavity for the cooling of strontium atoms

We have constructed a blue laser source consisting of an amplified, grating tuned diode laser that is frequency doubled by a KNbO3 crystal in a compact standing wave cavity and produces as much as 200 mW of internal second-harmonic power. We have analyzed the unusual characteristics of this standing wave cavity to clarify the advantages and disadvantages of this configuration as an alternative to a ring cavity for second-harmonic generation. We emphasize its efficiency and stability and the fact that it has an inherent walk-off compensation, similar to twin crystal configurations. We demonstrate its utility for laser cooling and trapping of earth alkalis by stabilizing the laser to the 461-nm transition of strontium, using a heat pipe, and then forming a magneto-optic trap of strontium from a Zeeman-slowed atomic beam.

Generation of 5-W deep-UV continuous-wave radiation at 266 nm by an external cavity with a CsLiB6O10 crystal

A Brewster-cut CsLiB6O10 crystal is employed as an external resonant frequency doubler to generate cw deep-UV radiation at 266 nm. We have generated 5.0 W of usable cw output power, which is 6.1 W in the crystal, for an incident green power of 9.6 W, corresponding to an internal conversion efficiency of 61.8%. The power obtained is, to our knowledge, three times higher than previously reported for cw 266-nm generation.

Efficient frequency doubling by a phase-compensated crystal in a semimonolithic cavity

In multiple-pass nonlinear frequency conversion devices, interacting waves may accumulate different phases, owing to dispersive elements in the system. Phase compensation is therefore necessary for efficient frequency conversion. We experimentally demonstrate phase compensation in a compact semimonolithic frequency-doubling cavity by using a periodically poled KTP crystal. The conversion efficiency of the crystal was found to decrease at high pump powers, owing to power-dependent thermal lensing. This experimental observation was supported by a theoretical calculation of the conversion efficiency in a cavity, considering the mismatch between the mode's thermally loaded and unloaded cavities. A design procedure was also presented to compensate for the thermal lensing effect. The highest conversion efficiency of 56.5%, corresponding to a second-harmonic power of 117.5 mW at 532 nm, was achieved with a cw Nd:YAG pump power of 208 mW.

High-power 457-nm light source by frequency doubling of an amplified diode laser

We demonstrate the generation of 150-mW blue coherent single-mode radiation at 457 nm in a compact and inexpensive setup. The light is generated by frequency doubling the radiation of a master oscillator power amplifier (MOPA) system in an enhancement cavity with a potassium niobate (KNbO3) crystal. The MOPA consists of a 914-nm single-mode diode laser and a broad-area diode laser (BAL) as the amplifier. The BAL is a multimode laser with a specified wavelength of 938 nm. Sufficient gain at 914 nm is obtained by antireflection coating the BAL front surface and by cooling it to -10 degrees C.

Stable 120-mW green output tunable over 2 THz by a second-harmonic generation process in a KTP crystal at room temperature

We report on 120-mW directly measured cw power at 532 nm from a tunable alpha -distributed-feedback laser diode near 1.064 microm frequency doubled in a KTP crystal operating room temperature inside a ring cavity. Our experimental setup allows us to scan frequencies up to 2 THz in the green-light domain and thus is extremely useful for iodine spectroscopy. We show good agreement between experimental results and theoretical predictions for the second-harmonic generation process.

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.

Unconditional quantum teleportation

Quantum teleportation of optical coherent states was demonstrated experimentally using squeezed-state entanglement. The quantum nature of the achieved teleportation was verified by the experimentally determined fidelity Fexp = 0.58 +/- 0.02, which describes the match between input and output states. A fidelity greater than 0.5 is not possible for coherent states without the use of entanglement. This is the first realization of unconditional quantum teleportation where every state entering the device is actually teleported.

Bichromatic frequency conversion in potassium niobate

Two frequency components of an IR laser beam near 980 nm are simultaneously coupled into two adjacent longitudinal modes of a passive ring resonator. A potassium niobate crystal inside the resonator converts the circulating IR light into coherent blue radiation. The total conversion efficiency is enhanced by a factor of 1.4 compared with that of conventional single-mode intracavity second-harmonic generation with the same circulating total power, and we obtain a total output power of 560 mW from 780-mW IR light incident upon the cavity. The spectra of the generated blue radiation and the circulating IR light contain a number of equidistant frequency components that are due to consecutive sum- and difference-frequency mixing.

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.

Frequency-tunable 500-mW continuous-wave all-solid-state single-frequency source in the blue spectral region

A compact source of stable cw single-frequency radiation at 473 nm has been realized by second-harmonic generation of a diode-pumped miniature Nd:YAG ring laser operating on the (4)F(3/2) - (4)I(9/2) laser transition. By use of potassium niobate (KNbO(3)), single-longitudinal-mode output powers of 500 mW cw with high stability and maximum optical-to-optical conversion efficiencies >81% are achieved. An external semimonolithic cavity permits mode-hop-free frequency tuning of blue radiation over as much as 20 GHz.

Sum-frequency generation of continuous-wave light at 194 nm

Over 2 mW of continuous-wave tunable 194-nm light is produced by sum-frequency mixing approximately 500 mW of 792-nm and 500 mW of 257-nm radiation in beta-barium borate (BBO). The powers in both fundamental beams are enhanced in separate ring cavities whose optical paths overlap in the Brewster-cut BBO crystal. Due to the higher circulating fundamental powers, the sum-frequency-generated power is nearly 2 orders of magnitude greater than previously reported values.

Bright tunable ultraviolet squeezed light

We have produced bright tunable squeezed light by second-harmonic generation in a singly resonant cavity. We have investigated the effect of input coupling and fundamental power on the squeezing. Up to 400 mW of continuous-wave mode-locked tunable squeezed light was produced at wavelengths as short as 389 nm, and more than 1.5 dB of squeezing was inferred.

Characterization of KNbO(3) crystal for frequency doubling of a tunable pulsed near-infrared laser

Using KNbO(3) crystals for second-harmonic generation in the blue spectral range, we have obtained conversion efficiencies as high as 53.7%. To our knowledge this value is the highest reported for a pulsed laser. A gainswitched nanosecond Ti:sapphire oscillator, amplified by a Cr:LiSrAlF(6) multipass amplifier, was used as the fundamental light source. The maximum energy obtained at the harmonic wavelength of 430 nm was 38 mJ for a bandwidth of 230 MHz.

Generation of 90-mW continuous-wave tunable laser light at 280 nm by frequency doubling in a KDP crystal

Laser light at a wavelength of 560 nm from a commercial ring dye laser has been frequency doubled in an external enhancement cavity with a KDP crystal. The cavity employs a new design consisting of only three mirrors, permitting a shorter cavity length as well as compensation for astigmatism and coma. With an input power of ~950 mW of green light, ~90 mW of UV light has been produced. The wavelength of the UV light can be tuned corresponding to +/-3 nm by angle tuning of the crystal, and the optical frequency can be scanned electronically up to +/-10 GHz.

Efficient operation of a room-temperature Nd:YAG 946-nm laser pumped with multiple diode arrays

Efficient pulsed room-temperature laser operation at 946 nm is reported for Nd:YAG pumped with multiple diode array bars. We achieved high pump brightness by collimating the outputs from individual bars and focusing them onto the end of a short 3-mm-diameter rod. An average power of 470 mW at 100 Hz was obtained with an optical slope efficiency of 15% based on incident pump power, and greater than 1 W of output was obtained at 300 Hz. Intracavity frequency doubling with KNbO(3) resulted in 40-70-mW output at 473 nm. Q-switched operation is also reported.

Efficient intracavity sum-frequency generation of 490-nm radiation by use of potassium niobate

Efficient sum-frequency generation of 910-nm radiation from a Ti:A1(2)O(3) laser and the circulating 1064-nm light inside a diode-pumped Nd:YVO(4) laser cavity has been achieved by use of b-axis KNbO(3). Blue-green output of 20 mW was generated with 100 mW of mixing power (910 nm) and a Nd:YVO(4) laser pumped by a 400-mW laser diode.

High-power second-harmonic generation with picosecond and hundreds-of-picosecond pulses of a cw mode-locked Ti:sapphire laser

A cw mode-locked Ti:sapphire laser was efficiently frequency doubled with a lithium triborate crystal in an external enhancement cavity. Second-harmonic output powers of 1.28 W and 860 mW have been generated at 399 nm with fundamental pulse widths of 1.5 and 320 ps, respectively. At the 1.5-ps pulse width the conversion efficiency was 75%. The spectral width of the 320-ps pulses, produced by modification of a laser cavity, is as narrow as the bandwidth of a normal cw, multimode, narrow-bandwidth Ti:sapphire laser. The frequency-doubled output can be thus used as a high-power, narrow-bandwidth light source in the UV region.

85% efficiency for cw frequency doubling from 1.08 to 0.54 ,microm

Conversion efficiency of 85% has been achieved in cw second-harmonic generation from 1.08 to 0.54 microm with a potassium titanyl phosphate crystal inside an external ring cavity. An absolute comparison between the experimental data and a simple theory is made and shows good agreement.