External Frequency Doubling Research Articles

All-Solid-State Q-Switched Laser Operating at 294.6 nm

We report a stable high-power all-solid-state Q-switched laser operating at 294.6 nm with a pulse width of 24 ns and a repetition rate of 20 kHz produced by intracavity sum-frequency generation and external frequency doubling in LiB3O5 and β-BaB2O4 crystals, respectively. Upon synchronizing the fundamental lasers, the maximum output power at 589 nm is 1.2 W, which is frequency doubled to produce up to 167.8 mW at 294.6 nm, thereby providing a conversion efficiency of 13.98%.

Experimental realization of high-efficiency blue light at 426 nm by external frequency doubling resonator

Second harmonic generation (SHG) is used to get continuous wave laser with a lot of applications, it is a major way to provide pump power for generating nonclassical states, especially for squeezed states and entanglement states. High-efficiency SHG resonant on atoms lines also provides laser sources for atomic entanglement generation, light-atom interaction and high-speed quantum memory. For the frequency-doubling process at 426 nm, the major challenge of increasing the conversion efficiency is the thermal effect caused by the absorption in crystal. The degradation of mode-match efficiency induced by the severely thermal effect limits the conversion efficiency of the second harmonic generator. Furthermore, the blue light induced infrared absorption (BLIIRA) in the nonlinear crystal intensifies the thermal effect, it makes the conversion efficiency of the frequency-doubling cavity and the stability of the output blue laser worse, and it is more serious at high input power. Based on the theoretical analysis of thermal lens, we find that the thermal lens should not be placed at the center of the crystal, the location of the equivalently thermals lens has a deviation from the center of the crystal. Follow the theoretical analysis of thermal lens, we design a ring cavity with a 10 mm-long periodically poled potassium titanyle phosphate (PPKTP) crystal to reduce the thermal lens effect induced mode-mismatch. The location of nonlinear crystal is adjusted precisely to reduce the mode-mismatch caused by the thermal lens under our theoretical analysis. Finally, we realized a high conversion efficiency blue laser at 426 nm with the conversion efficiency up to 83.1% with an output power of 428 mW after the adjustment of the crystal location, corresponding to our theoretical analysis well. The measured beam quality factors (<i>M</i><sup>2</sup> value) of the generated blue laser are <inline-formula><tex-math id="Z-20200217024354-1">\begin{document}$ M^2(x) = 1.05 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20191417_Z-20200217024354-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20191417_Z-20200217024354-1.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="Z-20200217024354-2">\begin{document}$ M^2(y) = 1.02 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20191417_Z-20200217024354-2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20191417_Z-20200217024354-2.png"/></alternatives></inline-formula>, respectively. The measured power stability of Generated Blue laser in 15 mins is 1.25%. The output power of the SHG is strong enough to provide pump power for the generation of the continuous variable squeezed vacuum state at 852 nm and the long-term stability of the output blue laser is also measured to be fine. To the best of our knowledge, the conversion efficiency is the highest-reported one at this wavelength. We believe that such high-performance frequency doubling system is a fundamental building block for quantum information science based non-classical states.

Highly efficient electro-optically Q-switched 473 nm blue laser

An external frequency doubling electro-optically Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) 473 nm blue laser was demonstrated. With absorbed pump energy of 48 mJ at 100 Hz repetition rate, about 2 mJ of 473 nm blue laser pulse energy was achieved by cascade frequency doubling. The second harmonic conversion efficiency was 64.5%, and overall optical-optical efficiency was 4.2%, respectively. The blue laser pulse width was less than 10 ns, and beam quality factor was less than 2.4.

Frequency-doubled green picosecond laser based on K3B6O10Br nonlinear optical crystal

We report a frequency-doubled green picosecond (ps) laser based on K3B6O10Br (KBB) nonlinear optical crystal with cutting angle of θ = 34.7° and φ = 30°. Through intracavity frequency doubling using a type I phase-matched KBB crystal with dimensions of 4 mm × 4 mm × 13.2 mm, the average output power of 185.00 mW green ps laser was obtained with a repetition rate of 80 MHz and pulse width of 25.0 ps. In addition, we present external frequency doubling using KBB crystal. The average output power of 3.00 W green ps laser was generated with a repetition rate of 10 kHz and pulse width of 38.1 ps, which corresponds to a pulse energy of 0.30 mJ and a peak power 7.89 MW, respectively. The experimental results show that KBB crystal is a promising nonlinear optical material.

2.4-watts second-harmonic generation in ppZnO:LN ridge waveguide for lithium laser cooling.

We present a simple all-solid-state laser source emitting 2.4 W of single-frequency light at 671 nm for laser cooling of lithium atoms. It is based on a diode-pumped solid-state laser, which is frequency doubled in a ppZnO:LN ridge waveguide with an internal doubling efficiency of 54%. We develop a simple theory for the thermal effects we observed at elevated fundamental powers, and compare the setup to a more efficient but more complex one with an external resonant frequency doubling cavity providing 5.2 W at 671 nm.

VECSEL systems for the generation and manipulation of trapped magnesium ions

Experiments in atomic, molecular, and optical (AMO) physics rely on lasers at many different wavelengths and with varying requirements on spectral linewidth, power, and intensity stability. Vertical external-cavity surface-emitting lasers (VECSELs), when combined with nonlinear frequency conversion, can potentially replace many of the laser systems currently in use. Here we present and characterize VECSEL systems that can perform all laser-based tasks for quantum information processing experiments with trapped magnesium ions. For photoionization of neutral magnesium, 570.6$\,$nm light is generated with an intracavity frequency-doubled VECSEL containing a lithium triborate (LBO) crystal for second harmonic generation. External frequency doubling produces 285.3$\,$nm light for resonant interaction with the $^{1}S_{0}\leftrightarrow$ $^{1}P_{1}$ transition of neutral Mg. Using an externally frequency-quadrupled VECSEL, we implement Doppler cooling of $^{25}$Mg$^{+}$ on the 279.6$\,$nm $^{2}S_{1/2}\leftrightarrow$ $^{2}P_{3/2}$ cycling transition, repumping on the 280.4$\,$nm $^{2}S_{1/2}\leftrightarrow$ $^{2}P_{1/2}$ transition, coherent state manipulation, and resolved sideband cooling close to the motional ground state. Our systems serve as prototypes for applications in AMO requiring single-frequency, power-scalable laser sources at multiple wavelengths.

Comparison of Molecular Iodine Spectral Properties at 514.7 and 532 nm Wavelengths

Abstract We present results of investigation and comparison of spectral properties of molecular iodine transitions in the spectral region of 514.7 nm that are suitable for laser frequency stabilization and metrology of length. Eight Doppler-broadened transitions that were not studied in detail before were investigated with the help of frequency doubled Yb-doped fiber laser, and three of the most promising lines were studied in detail with prospect of using them in frequency stabilization of new laser standards. The spectral properties of hyperfine components (linewidths, signal-to-noise ratio) were compared with transitions that are well known and traditionally used for stabilization of frequency doubled Nd:YAG laser at the 532 nm region with the same molecular iodine absorption. The external frequency doubling arrangement with waveguide crystal and the Yb-doped fiber laser is also briefly described together with the observed effect of laser aging.

High Conversion Efficiency and Power Stability of 532 nm Generation from an External Frequency Doubling Cavity

We present a high-efficiency 532 nm green light conversion from an external cavity-enhanced second harmonic generation (SHG) with a periodically poled KTP crystal (PPKTP). The cavity is a bow-tie ring configuration with a unitized structure. When the impedance matching is optimized, the coupling efficiency of the fundamental is as high as 95%. Taking into account both the high power output of the second harmonic and the stability of the system, we obtain over 500 mW green passing through the output cavity mirror, corresponding to a net conversion efficiency higher than 75.2%. Under these operating conditions, the power stability is better than ±0.25% during 5 h. It is the highest conversion efficiency and power stability ever produced in the bow-tie ring cavity with PPKTP for 532 nm generation.

LD side-pumped 41 W high beam quality acousto-optical Q-switched single-rod Nd:YAG laser

We report a LD side-pumped high beam quality (M 2 = 1.20 and M 2 = 1.19) acousto-optic (AO) Q-switched single-rod Nd:YAG laser with a TEM00-mode dynamic stable cavity. At the pump power of 600 W, 41 W TEM00-mode 1064 nm laser was achieved with electro-optical conversion efficiency of 7%. The repetition rate and pulse width were 30 kHz and 102 ns, respectively with pulse energy of 1.4 mJ and peak power of 13 kW. Up to 24 W of 532 nm green laser was generated by external frequency doubling, corresponding to 59% optical conversion efficiency.

Passively mode-locked Yb:YAG thin-disk laser with pulse energies exceeding 13 μJ by use of an active multipass geometry

We demonstrate the generation of high-energy picosecond pulses directly from a thin-disk laser oscillator by employing a self-imaging active multipass geometry. Stable single-pulse operation has been obtained with an average output power in excess of 50 W, excluding a cw background of 8%, at a repetition rate of 3.8 MHz. Self-starting passive mode locking was accomplished using a semiconductor saturable absorber mirror. The maximum pulse energy was 13.4 microJ at a pulse duration of 1.36 ps with a time-bandwidth product of 0.34. Single-pass external frequency doubling with a conversion efficiency of 60% yielded >28 W of average power at 515 nm.

Frequency-stabilized Nd:YVO4 thin-disk laser

We have developed a Nd:YVO4 thin-disk laser at 914 nm with single-frequency operation and active frequency stabilization to a low-finesse reference cavity. The spectral density of laser frequency noise is analysed by means of noise measurements at the error point of the frequency control loop. To address the 31S0→33P1 magnesium intercombination line at 457 nm, we use an external frequency doubling stage based on periodically poled KTiOPO4 for the generation of more than 150-mW output power at 457 nm. Optical beat signal measurements at 457 nm with a frequency-stable dye laser show a short-time line width of the thin-disk laser of less than 100 kHz.

4W continuous-wave narrow-linewidth tunable solid-state laser source at 546nm by externally frequency doubling a ytterbium-doped single-mode fiber laser system

A high-power continuous-wave coherent light source at 545.5nm is described. We use 8.3W from a solid-state ytterbium-doped single-mode fiber oscillator/amplifier system as input into an external frequency doubling stage. This system produces up to 4.1W of stable green single-frequency laser radiation. We characterize the light source by performing absorption spectroscopy on iodine across the full tuning range of the fiber laser and saturation spectroscopy on one strong iodine line of the doppler-broadened spectrum.

Nanosecond pulse generation in a passively Q-switched Yb-doped fiber laser by Cr/sup 4+/:YAG saturable absorber

We explored efficient nanosecond pulse generation in a passively Q-switched cladding-pumped Yb-doped fiber laser by use of an external-cavity configuration containing a Cr/sup 4+/:YAG saturable absorber crystal. By exploiting passive Q-switched regime and stimulated Brillouin scattering, pulses of durations as short as 2.7 ns, corresponding to a peak power of /spl sim/9 kW, have been achieved. The laser was tunable over 70 nm and green output power generation was obtained by external frequency doubling in a KTP crystal.

Focus on Lasers and Optics

Focus on Lasers and Optics

Configuration to improve second-harmonic-generation conversion efficiency.

The dependence of second-harmonic-generation (SHG) conversion efficiency on the intercrystal phase shift between two nonlinear crystals is analyzed with heuristic theory, and a novel scheme for SHG with two cascaded nonlinear crystals and a polarization modulator is proposed. More than 30 W output power is obtained experimentally at 532 nm with 70% external doubling efficiency. To the best of our knowledge, this is the highest conversion efficiency obtained with LiB3O5 crystal external frequency doubling. This scheme provides a simple and effective method for improving second-harmonic conversion efficiency.

Frequency and Output Power Stabilization Using Novel Voice-Coil-Motor Actuator.

Novel voice-coil-motors (VCM) are applied to an injection-locked Nd: YAG laser and a frequency quadrupled continuous-wave Nd: YAG laser. The injection locked laser is developed for TAMA300 interferometric gravitational wave detection. Using multi-rod laser design and the injection-locking technique, we achieved 10 W output power and single frequency lasing simultaneously. This laser is frequency-stabilized to a highfinesse Fabry-Perot cavity. We have achieved long term reliability, low noise output and stable locking in external resonant frequency doubling of a beta-Barium Borate (BBO) cavity by the use of a novel VCM actuator and high quality Czochralski-grown BBO.

11-W single-frequency 532-nm radiation by second-harmonic generation of a miniature Nd:YAG ring laser

A compact and efficient source of cw single-frequency radiation at 532 nm with excellent long-term stability has been realized by external frequency doubling of a diode-pumped miniature Nd:YAG ring laser. With a semimonolithic MgO:LiNbO(3) resonator an optical-to-optical conversion efficiency of 89% from 1064 to 532 nm at an output power of 1.1 W was achieved, with a wall plug efficiency of 9%. This system represents an ideal pump source for narrow-linewidth cw optical parametric oscillators with good frequency stability.

Visible picosecond pulse generation in a frequency doubled optical parametric oscillator based on LiB 3O 5

We report the attainment of transform-limited pulses across the entire tuning range of a high-repetition-rate, synchronously-pumped picosecond optical parametric oscillator (SPOPO) based on LiB 3O 5, by the inclusion of dispersion compensation in the positive dispersive regime of the crystal. This system which is synchronously pumped by 1.1 ps pump pulses from a self-mode-locked Ti:sapphire laser at 81 MHz, generated transform-limited signal pulses with durations of 1–1.2 ps and idler pulses with durations of 2–2.2 ps over the continuous wavelength range of 1.16–2.26 μm at average powers of 580 mW. By external frequency doubling output signal pulses from the SPOPO in noncritically phase-matched, temperature-tuned LiB 3O 5, we have produced transform-limited picosecond pulses in the visible range from 584 to 771 nm at average powers of up to 68 mW. Second harmonic pulses with durations between 840 and 880 fs have been obtained for signal durations of 1–1.2 ps.

On the measurement of dipole moments in different electronic states of aromatic molecules: 1-fluoronaphthalene as an example

This work presents studies on the influence of homogenous and static electric fields upon the 000 vibrational band in the A 1A′ ← X 1A′ electronic transition of the free asymmetric 1-fluoronaphthalene molecule. Narrow-band laser radiation at 313.8 nm was generated by means of external frequency doubling of the output of a cw ring dye laser system. The jet-cooled molecules were excited between two capacitor plates. Shifts and splittings of certain rovibronic transitions due to the Stark effect could be measured and evaluated. These data yielded accurate values for all dipole moment components involved in the vibronic transition. Then, field-dependent intensities could be calculated and, accordingly, complete Stark spectra were simulated.

Stark effect and fluorescence quenching in the S1 ← S0 000 rovibronic spectrum of pyrazine

We report high resolution Stark effect measurements on the rotational spectrum of the S1 ← S0 000 vibronic transition of free, jet-cooled pyrazine at 323.9 nm. Tunable, narrowband UV laser radiation was generated within an external frequency doubling unit fed by the output of a cw ring dye laser. As pyrazine is a nonpolar molecule, application of very strong electric fields up to 100kV/cm was essential to induce an appreciable dipole moment. The measurements showed an unexpected, dramatic decrease in the overall fluorescence from the upper rotational states. The excitation intensities monotonically decline with increasing electric field without any other structure arising. The components of the P(1) band were studied in detail, exhibiting individual behaviour of both decrease in intensity and Stark shift. The latter gives rise to certain estimations concerning the molecular polarizability. It seems likely that interaction with a large density of high energetic rovibronic states of the T1 system is responsible for the fluorescence quenching.