Periodically Poled MgO:LiNbO3 Research Articles

Optimization of frequency-doubled Er-doped fiber laser for miniature multiphoton endoscopy.

Frequency-doubled femtosecond Er-doped fiber laser is a low-cost and portable excitation source suitable for multiphoton endoscopy. The frequency-doubled wavelength at 780nm is used to excite the intrinsic fluorescence signal. The frequency-doubling with a periodically poled MgO : LiNbO3 (PPLN) is integrated in the distal end of the imaging head to achieve fiber connection. The imaging speed is further improved by optimizing the excitation laser source. A 0.3-mm length of PPLN crystal is selected and the Er-doped fiber laser is manipulated to match its bandwidth with the acceptance bandwidth of the PPLN. Through this optimization, a reduced pulsewidth of 80fs of the frequency-doubled pulse is achieved. All-fiber dispersion compensation and pulse compression by single mode fiber is conducted, which makes the fiber laser directly fiber-coupled to the imaging head. An imaging speed of 4 frames / s is demonstrated on ex vivo imaging of unstained biological tissues, which is 10 times faster than our previous study using a 1-mm-long PPLN. The results show that miniature multiphoton endoscopy using frequency-doubled Er-doped fiber laser has great potential for clinical applications.

A 100 kHz Narrow-Pulse-Width Mid-Infrared Optical Parametric Oscillator Based on PPMgLN Crystal

We report a narrow pulse width optical parametric oscillator based on periodically poled MgO:LiNbO3 (PPMgLN) with a high repetition rate under quasi-phase matched conditions. When the maximum pumping power of the 1,064-nm laser was 14.57 W, the acousto-optical (A-O) Q-switch repetition rate was 100 kHz, and the PPMgLN crystal grating period was 29.5 μm. A 1,474-nm signal light output power of 4.21 W and a 3,828 nm idler light output power of 1.547 W were obtained, corresponding to a pulse width of 9.52 ns and 9.65 ns, respectively. The overall optical–optical conversion efficiency was 39.5%. Additionally, by changing the temperature from 25°C to 150°C, a tunable signal wavelength of 1,474–1,499 nm and idler wavelength at 3,676–3,828 nm of the output laser were achieved.

High-repetition-rate narrow pulse width mid-infrared optical parametric oscillator based on PPMgLN crystal

This paper reports a narrow pulse width optical parametric oscillator (OPO) based on periodically poled MgO:LiNbO3 (PPMgLN). When the maximum pumping power of the 1064 nm laser was 26.07 W, the acousto-optical (AO) Q-switch repetition rate was 70 kHz and the PPMgLN crystal grating period was 29 μm; a 3840 nm mid-infrared light output power of 4.86 W was obtained at 150 °C, corresponding to a pulse width of 9.56 ns. The optical–optical conversion efficiency was about 18.6%. In addition, by changing the temperature between 25 °C to 200 °C, a tunable mid-infrared wavelength of 3765–3974 nm output laser was achieved.

2.1 μm four-mirror standing-wave optical parametric oscillator with high brightness and efficiency

We report a high-brightness and high-efficiency degenerate periodically poled MgO:LiNbO3 (PPMgLN) optical parametric oscillator (OPO), configured with a four-mirror standing-wave cavity and pumped by a Q-switched Nd:YVO4 laser. Attributed to the successful mode matching of four-mirror standing-wave cavity, we have obtained good beam qualities both in single-pass and double-pass geometry. The beam qualities of single-pass pump geometry are M2 ∼ 1.6 and 1.7 in the horizontal and vertical directions, and the beam qualities of double-pass pump geometry are M2 ∼ 1.8 and 1.9. Optical to optical conversion efficiencies of 38% and 55% are achieved, respectively. With a volume Bragg grating used as the output coupler, we achieved a narrow linewidth of less than 2 nm.

A highly efficient 3.2 μm optical parametric oscillator pumped by a passively Q-switched Nd:YVO4 laser

We describe a compact all-solid-state singly resonant optical parametric oscillator (SRO) based on a Cr4+: YAG Q-switched Nd:YVO4 laser. The SRO is based on periodically poled MgO:LiNbO3 (PPMgLN) as the nonlinear material. By exploiting a 35 mm PPMgLN crystal, we achieved the SRO operation threshold at a pump power of only 140 mW. At 1.78 W of pump laser with a pulse width of 10 ns and a repetition of 50 kHz, 360 mW average power at 3.2 μm and a mid-infrared conversion efficiency of 20% were achieved.

High-efficiency near-degenerate PPMgLN optical parametric oscillator with a volume Bragg grating

We demonstrate a high-efficiency near-degenerate periodically poled MgO:LiNbO(3) (PPMgLN) optical parametric oscillator (OPO) using a volume Bragg grating (VBG) output coupler (OC) pumped by a multilongitudinal Q-switched Nd:YVO(4) laser at 20 kHz repetition rate. A total parametric power of 4.3 W with a conversion efficiency of 60% is achieved in a double-pass pump configuration. The output power improvement over the case of a single-pass pump is nearly 60%. Both the signal and the idler bandwidths are less than 40 GHz and are confined within 170 GHz bandwidth at 2128.8 nm. Such efficiency is, to our knowledge, the highest ever achieved from a degenerate OPO using a VBG OC.

A robust method for frequency stabilization of 556-nm laser operating at the intercombination transition of ytterbium

A frequency-stabilized 556-nm laser is an essential tool for experimental studies associated with 1S0-3P1 intercombination transition of ytterbium (Yb) atoms. A 556-nm laser light using a single-pass second harmonic generation (SHG) is obtained in a periodically poled MgO:LiNbO3 (PPLN) crystal pumped by a fiber laser at 1111.6 nm. A robust frequency stabilization method which facilitates the control of laser frequency with an accuracy better than the natural linewidth (187 kHz) of the intercombination line is developed. The short-term frequency jitter is reduced to less than 100 kHz by locking the laser to a home-made reference cavity. A slow frequency drift is sensed by the 556-nm fluorescence signal of an Yb atomic beam excited by one probe beam and is reduced to less than 50-kHz by a computer-controlled servo system. The laser can be stably locked for more than 5 h. This frequency stabilization method can be extended to other alkaline-earth-like atoms with similar weak intercombination lines.

外腔式宽调谐被动调QNd:YVO4/PPMgLN光学参量振荡器

A wide-tunable, low-threshold, extra-cavity singly resonant optical parametric oscillator(OPO) has been reported, which is based on periodically poled MgO:LiNbO3 (PPMgLN). The OPO system, compact and simple, adopts a passively Q-switched Nd:YVO4 laser as the pump source and realizes quasi-phase-matched optical parametric oscillation at room temperature. The threshold value of the OPO system is only 0.27 W (single pulse energy of 4.5 μJ, pulse duration of 35 ns) at 1 064 nm. When the pump power is 1.35 W (pulse energy of 8.2 μJ, pulse duration of 35 ns), an idler output power of 161.9 mW at 3.202 μm, and a signal output power of 98.5 mW at 1.594 μm have been achieved, and this corresponds to a whole (idler+signal) optic-optic conversion efficiency of 19.3%. By shifting the PPMgLN crysta

Temperature tunable infrared optical parametric generation based on periodically poled MgO:LiNbO3 crystals

By using a short-pulse field, periodically poled grating (A = 29 μm) was successfully fabricated in a 1.0 mm-thick MgO:LiNbO3 (mole fraction of doped MgO is 5%). A high-repetition-rate optical parametric generation (OPG) based on periodically poled MgO:LiNbO3 (PPMgLN) was pumped by a 1.064 μm acousto-optically Q-switched Nd:YVO4 laser. With 3 W of input pump power, 44 mW of output signal power was obtained at a conversion efficiency of 1.5%. Tunable infrared (IR) output from 1.4538–1.4750 μm was also obtained by tuning the temperature of PPMgLN, which is 45°C–160°C.

Compact efficient optical parametric generator internal to a Q-switched Nd: YVO4 laser with periodically poled MgO:LiNbO3

This paper demonstrates a compact efficient optical parametric generator internal to a Q-switched diode-end-pumped Nd:YVO4 laser with periodically poled MgO:LiNbO3(PPMgLN). With the Q-switch set at a repetition rate of 25kHz and the PPMgLN crystal operated at room temperature (25°C), the intracavity optical parametric generator threshold was reached as a diode pump power of 0.9 W. A maximum signal output power of 0.34 W with a pulse width of 25 ns and a beam quality factor of 1.4 was obtained at an incident diode power of 3.4 W, leading to a conversion efficiency of 10% with a slope efficiency of 14.4%. By varying the crystal temperature from 25 to 200°C, the output signal wavelengths were tuned in range of 1506-1565 nm. Over a 30-minutes interval, the instability of the signal power was measured to be less than 1%. In addition, the threshold pump intensity for the intracavity optical parametric generator is theoretically investigated, and the obtained result is in good agreement with the experimental results.

High‐Efficiency Intracavity Continuous‐Wave Green‐Light Generation by Quasiphase Matching in a Bulk Periodically Poled MgO:LiNbO3 Crystal

908 mW of green light at 532 nm were generated by intracavity quasiphase matching in a bulk periodically poled MgO:LiNbO3 (PPMgLN) crystal. A maximum optical‐to‐optical conversion efficiency of 33.5% was obtained from a 0.5 mm thick, 10 mm long, and 5 mol% MgO:LiNbO3 crystal with an end‐pump power of 2.7 W at 808 nm. The temperature bandwidth between the intracavity and single‐pass frequency doubling was found to be different for the PPMgLN. Reliability and stability of the green laser were evaluated. It was found that for continuous operation of 100 hours, the output stability was better than 97.5% and no optical damage was observed.

Effect of MgO doping of periodically poled lithium niobate on second-harmonic generation of femtosecond laser pulses

We theoretically analyze type-I broadband second-harmonic generation (SHG) of femtosecond laser pulses based on a quasi-phase-matching configuration in periodically poled congruent LiNbO3 (LN) andperiodically poled MgO:LiNbO3 (PPMgLN) (5% and 7%). Group-velocity matching (GVM) can be achieved at the fundamental waves of 1.59, 1.56, and 1.55 microm for SHG when the three types of crystals have grating periods of 22.31, 20.07, and 23.45 microm, respectively. It is found that the central wavelength of the fundamental wave for GVM will increase with the decrease of MgO doping in LN. It is concluded that the shift of the GVM central wavelength is due to the difference of MgO doping, which changes the dispersion of the crystal. Therefore, tunable and high efficiency broadband SHG of femtosecond laser pulses in a long crystal can be realized by selecting different doping rates of PPMgLN.

Visible Micro Solid-State Lasers

We review the recent trends of visible light sources based on nonlinear frequency conversion from the Nd3+-doped micro-lasers. In order to evaluate the emission properties of 1.3, 1.0, and 0.9 in Nd3+-ion doped materials, the spectroscopic parameters were summarized. Recently appeared Nd: GdV4O has the large absorption and emission cross-sections with high thermal conductivity, as high as YAG. After the demonstration of near quantum limit highly efficient operation in Nd: GdVO4, the intra-cavity frequency doubled micro-laser was reviewed as a high power compact green laser. On the other hand, we have demonstrated the high power stable green and deep blue laser under extra-cavity frequency doubling with periodically-poled MgO: LiNbO3 (PPMgLN) for quasi-phase matched second harmonic generation (QPM-SHG). Finally, edge pumped Yb: YAG microchip laser was discussed for the high-power visible microchip lasers.

Continuous-wave ultraviolet generation at 354nm in a periodically poled MgO:LiNbO3 by frequency tripling of a diode end-pumped Nd:GdVO4 microlaser

Continuous-wave UV radiation at 354nm, the third harmonic of a Nd:GdVO4 laser operating at 1063nm, is reported from single-pass cascaded, first-order periodically poled MgO:LiNbO3 (PPMgLN) crystals. A high-voltage multipulse poling method was used in order to realize PPMgLN with uniform domain period (Λ) of micron-order width and 50% duty cycle along the entire crystal length. Initially, second-harmonic generation of the 1063nm Nd:GdVO4 laser at 2.1%∕W conversion efficiency, producing 1.15W at 531nm, is obtained from a 10-mm-long PPMgLN with Λ=6.95μm. Sum frequency mixing of this 531nm light with the residual 1063nm fundamental radiation in a 3.6-mm-long PPMgLN with Λ=1.78μm produces 47mW of UV with 3.9%∕W∕cm normalized conversion efficiency.

High-power continuous-wave ultraviolet generation by singlepass frequency doubling in periodically poled MgO:LiNbO 3

Perfect first-order quasi-phase matching for singlepass ultraviolet (UV) second-harmonic generation in a periodically poled MgO:LiNbO3 (PPMgLN) is reported. At room temperature, continuous-wave UV light power of 71.7 mW at 372 nm was achieved with an effective nonlinear coefficient over 20 pm/V (nearly equal to the ideal for PPMgLN).