High efficiency and high energy parametric wavelength conversion using a large aperture periodically poled MgO:LiNbO3

We have demonstrated an efficient high energy 2 μm laser generation with a 36 mm long large aperture 5 mol% MgO-doped periodically poled LiNbO₃ (PPMgLN) nonlinear optical crystal. A high power Q-switched Nd:YAG laser (1.064 μm) was used to pump the quasi-phase matched (QPM) optical parametric oscillator (OPO). A total output energy of 186 mJ with 58% slope efficiency was obtained in two separate beams at 2 μm.     

Tunable terahertz generation from one CO2 laser in a GaSe crystal

Coherent terahertz pulses have been generated at a range of 236.3-1104.5 μm (0.27-1.3 THz) by one CO₂ laser with dual-wavelength output based on collinearly phase-matched different frequency generation (DFG) in a GaSe crystal. This source has the advantages of compact and simplicity for tuning. The output power of the THz pulse and phase-matching conditions were investigated. The maximum single pulse energy of 11 nJ was generated at a frequency of 1.23 THz (243.6 μm), corresponding to a peak output power 182 mW.     

High repetition rate mid-infrared generation with singly resonant optical parametric oscillator using multi-grating periodically poled MgO:LiNbO3

A high repetition rate mid-infrared singly resonant optical parametric oscillator (OPO) using MgO-doped multi-grating periodically poled LiNbO₃ (MgO:PPLN) is demonstrated. A 1064 nm Q-switched Nd:YVO₄ laser at 10 kHz repetition rate and pulse width of 17.8 ns was used to pump the OPO. The period of the quasi-phase matched (QPM) grating in the multi-grating MgO:PPLN chip varied from 25.5 to 31.5 μm in steps of 0.5 μm. This corresponds to the generation of a signal beam from 1.37 to 1.64 μm and an idler beam from 3.0 to 4.8 μm, respectively. A maximum signal power of 250 mW and idler power of 140 mW has been obtained with an input pump beam of power 1.92 W, for a grating period of 30.5 μm. A maximum optic-optic conversion efficiency of 20% and 7.4% in the idler has been observed. It has been observed that the output power increases as the period of the grating increases.     

Pulse LDA-pumped single-frequency Nd:YVO4-KTP green laser using Brewster plate

A pulse laser-diode-array (LDA)-pumped, single-axial-mode, intracavity frequency-doubled Nd:YVO₄ laser has been demonstrated by using an birefringent filter consisting of a KTP crystal and two Brewster plates (BP). Up to 72.4 mW average output power is obtained for 800 mW pumping power with an optical-to-optical conversion efficiency of 9.1%. The maximum peak power of the single-frequency green laser is 22.3 W with the pulse width 162 μs.     

RF discharge slab CO laser operating in both fundamental and first-overtone bands

A compact sealed-off cryogenically cooled radio frequency (RF) discharge slab CO laser, operating in both first-overtone (FO) and fundamental band (FB), was launched. Repetitively pulsed and CW modes of RF discharge excitation were studied. Average FB output power was up to 12 W, with laser efficiency 14%. The multiline FB laser spectrum was observed within the wavelength range ∼5.1-5.4 μm. An optical scheme “frequency selective master oscillator - laser amplifier” was applied for getting FB tuning. Single line FB lasing with average power up to several tens of mW was observed on ∼100 FB vibrational-rotational transitions of CO molecule within the spectral range ∼5.0-6.5 μm. Multiline FO lasing was observed on ∼80 spectral lines within the spectral range ∼2.5-4.0 μm, with maximum single line average output power 12 mW. Total output power of the slab FO CO laser came up to 0.3 W, with maximum laser efficiency 0.5%. Results of parametric studies of the FB and FO slab CO laser including complicated time behavior for laser pulses on different FO vibrational-rotational transitions are discussed.     

Characteristics of a flowing He-SrCl2 vapor laser

An experimental investigation on the characteristics of a flowing He-SrCl₂ vapor laser is carried out. The output power as a function of the SrCl₂ vapor pressure is presented by calculating the radial temperature distribution of the discharge tube. The temporal dependences of the discharge current pulse on the laser pulses at 1 μm, ∼ 3 μm and 6.45 μm lines in strontium atom and ion, as well as the spot modes of the laser beam are measured and analyzed under different laser output power.     

Continuous-tunable 4.144-4.851 μm twin-MgO:PPLN cascaded optical parametric generator pumped by a 1.342 μm Nd:GdVO4 laser

An all-solid-state mid-infrared optical parametric generator with wide tunability by using multi-grating periodically poled 5 mol.-% MgO-doped lithium niobate (MgO:PPLN) is reported. The pump source is a diode-pumped Q-switched Nd:GdVO₄ laser operated at 1.342 μm with pulse width of 150 ns and repetition rate of 50 kHz. To extend the interaction length, two identical multi-grating MgO:PPLN crystals have been cascaded in the OPG system. When the incident pump average power is 10 W, the obtained maximum idler output power is 340 mW at 4.144 μm. Compared with only using one multi-grating MgO:PPLN crystal, the obtained idler output power increases by 20.1%. 4.144-4.851 μm continuous-tunable idler output is obtained with six grating periods from 29 to 31.5 μm and temperature from 40 to 200 °C. To our knowledge, this is the first time to use 1.342 μm laser as the pump source of OPG.     

41 mW high average power picosecond 177.3 nm laser by second-harmonic generation in KBBF

We report on the generation of high average power, high repetition rate, and picosecond (ps) deep-ultraviolet (DUV) 177.3 nm laser. The DUV laser is produced by second-harmonic generation of a frequency-tripled mode-locked Nd: YVO₄ laser (<15 ps, 80 MHz) with KBBF nonlinear crystal. The influence of different fundamental beam diameters on DUV output power and KBBF-SHG conversion efficiency are investigated. Under the 355 nm pump power of 7.5 W with beam diameter of 145 μm, 41 mW DUV output at 177.3 nm is obtained. To our knowledge, this is the highest average power for the 177.3 nm laser. Our results provide a power scaling by three times with respect to previous best works.     

800 mW/1484 nm highly efficient two-cascaded phosphosilicate Raman fiber laser pumped by Nd:YVO4 solid-state laser

Using 1064 nm CW Nd:YVO₄ solid-state laser as a pump, 1-km phosphosilicate fiber and cascaded cavities with two pairs of fiber Bragg grating mirrors for 1239 and 1484 nm, we obtained a CW 800 mW/1484 nm Raman fiber laser (RFL) for an actual incident pump power of about 2 W (Nd:YVO₄ power of 6.90 W). The conversion efficiency is as high as 40%. To the best of our knowledge, this is the highest conversion efficiency of RFL pumped by solid-state laser. The output power instability at 1484 nm in half an hour is less than 3%. In addition, the numerical simulations are also performed. Good agreement between the results of numerical simulation and the results of the experiment has been demonstrated.     

Widely and continuously tunable optical parametric generator infrared laser

The experimental results of a high efficiency infrared laser are demonstrated on a quasi phase matched optical parametric generator in PPMgLN (5% MgO doping) pumped by a 1064 nm Nd:YAG laser. A broad continuous signal spectrum 1.56?C1.67 ??m are obtained by tuning the crystal temperature from 20°C to 200°C. When the average pump power is 1.82 W with about 70 ns pulse duration operating at a repetition rate of 10 kHz, the maximum total output power of the PPMgLN OPG is about 323.58 mW consisting of 210 mW of 1.639 ??m signal radiation and 113.58 mW of 3.02 ??m idler radiation.     

LD end-pumped intracavity frequency doubled Yb:YAG laser

A laser diode end-pumped 10 at.% doped Yb:YAG microchip crystal intracavity frequency doubled all solid-stated green laser is reported in this paper. Using one plano-concave resonator, with the pump power of 1.2 W, 44.2 mW TEM₀₀ continuous wave (CW) laser at 525 nm was obtained, the optical conversion efficiency was about 3.7%. When a Cr:YAG crystal with initial transmission of 95.5% inserted in the resonator, the maximum output power of 6.4 mW, pulse duration width of 49.1 ns, pulse repetition rate of 2.45 kHz, and peak power of 53.1 W at 515 nm were achieved when the pump power was 1.2 W. The wavelength changed from 525 nm to 515 nm and the threshold was only 725 mW.     

26.3-W continuous-wave, diode-double-end-pumped all-solid-state Nd:GdVO4 laser operating at 1.34 μm

A high-power continuous-wave (CW) all-solid-state Nd:GdVO₄ laser operating at 1.34 μm is reported here. The laser consists of a low doped level Nd:GdVO₄ crystal double-end-pumped by two high-power fiber-coupled diode lasers and a simple plane-parallel cavity. At an incident pump power of 88.8 W, a maximum CW output of 26.3 W at 1.34 μm is obtained with a slope efficiency of 33.7%. To the best of our knowledge, this is the highest output at 1.34 μm ever generated by diode-end-pumped all-solid-state lasers.     

Continuous-wave high-power multi-pass pumped thin-disc Nd:GdVO4 laser

A thin-disc Nd:GdVO₄ laser in multi-pass pumping scheme was developed. Continuous-wave output power of 13.9 W at 1.06 μm for an absorbed power at 808 nm of 22 W was demonstrated from a 250-μm thick, 0.5-at.% Nd:GdVO₄ in a 4-pass pumping; the slope efficiency in absorbed power was 0.65, or 0.47 in input power. Output performances were also investigated under diode laser pumping at 879 nm, directly into the emitting ⁴F_3/2 level: maximum power of 3.6 W was obtained at 6.2 W of absorbed power with 0.69 slope efficiency. Compared with pumping at 808 nm, into the highly absorbing ⁴F_5/2 level, improvements of laser parameter in absorbed power (increase of slope efficiency, decrease of threshold) were obtained, showing the advantages of the pumping into the emitting level. However, the laser performances expressed vs. the incident power were modest owing to the low absorption efficiency at 879 nm. Thus, increased number of passes of the medium would be necessary in order to match the performances in input power obtained under 808-nm pumping.     

Low-pump-threshold tunable optical parametric oscillator using periodically poled MgO:LiNbO3

We fabricated and characterized periodically poled MgO:LiNbO₃ device with five gratings in 0.5 μm increments from 29 μm to 31 μm for optical parametric oscillator (OPO). The OPO operation threshold is 30 μJ using this device with a 50 mm effective length. At 560 mW input pump power, we have achieved 300 mW of the total output power, and the conversion efficiency is 54%. Multi-periods and temperatures tuning of the OPO yields a signal wavelength range from 1.45 to 1.72 μm and an idler wavelength range from 2.8 to 4.05 μm in the mid infrared.     

Widely tunable, high-repetition-rate, dual signal-wave optical parametric oscillator by using two periodically poled crystals

This paper reports on a high-repetition-rate dual signal-wave (DSW) optical parametric oscillator (OPO) operating at the 1.5 μm band with tunable wavelength intervals from 2.5 nm to 69.1 nm. Two periodically poled crystals, a periodically poled lithium niobate (PPLN) with multiple gratings and a single grating MgO-doped PPLN (PPMgOLN), are cascaded in the same OPO cavity to generate dual signal-waves by using quasi-phase-matched (QPM) technique. The pump source was a Q-switched diode-pumped Nd:YVO₄ laser operating at 50 kHz. At an incident pump power of 3 W, an average output power of 169.6 mW at 1489.2 nm and 1558.3 nm has been achieved.     

Diode-pumped Nd:LuVO4-Nd:YLiF4 crystals blue laser at 489 nm by intracavity sum-frequency-mixing

We present a laser architecture to obtain continuous-wave blue radiation at 489 nm. An 809 nm diode-pumped the Nd:LuVO₄ crystal emitting at 916 nm. A part of the pump power was then absorbed by the Nd:LuVO₄ crystal. The remaining was used to pump the Nd:YLiF₄ (Nd:YLF) crystal emitting at 1047 nm. Intracavity sum-frequency mixing at 916 and 1047 nm was then realized in a LiB₃O₅ (LBO) crystal to reach the blue radiation. We obtained a continuous-wave output power of 425 mW at 489 nm with a pump laser diode emitting 18.4 W at 809 nm.     

High-power, continuous-wave Ti:sapphire laser pumped by fiber-laser green source at 532 nm

We report the first experimental demonstration of efficient and high-power operation of a Ti:sapphire laser pumped by a simple, compact, continuous-wave (cw) fiber-laser-based green source. The pump radiation is obtained by direct single-pass second-harmonic-generation (SHG) of a 33 W, cw Yb-fiber laser in a 30-mm-long MgO:sPPLT crystal, providing 11 W of single-frequency green power at 532 nm in TEM₀₀ spatial profile with power and frequency stability better than 3.3% and 32 MHz, respectively, over 1 h. The Ti:sapphire laser is continuously tunable across 743-970 nm and can deliver an output power up to 2.7 W with a slope efficiency as high as 32.8% under optimum output coupling of 20%. The laser output has a TEM₀₀ spatial profile with M²<1.44 across the tuning range and exhibits a peak-to-peak power fluctuation below 5.1% over 1 h.     

Diode-end-pumped composite Nd:YVO4 yellow laser based on intracavity frequency-doubled self-Raman laser

We report an intracavity frequency-doubled Q-switched self-Raman yellow laser at 587 nm. A composite Nd:YVO₄ crystal was utilized as self-Raman gain medium. The maximum average output power of yellow light obtained was 1.5 W at the incident pump power of 30 W and at a repetition rate of 50 kHz, corresponding to the optical conversion efficiency of 5%. The shortest pulse width, the maximum pulse energy and the highest peak power were measured to be 5.8 ns, 46.7 μJ and 5.9 kW, respectively.     

Graphene-based passively Q-switched 2 μm thulium-doped fiber laser

We demonstrated stable pulses generation at 2 μm in a passively Q-switched thulium-doped fiber laser using a few layer graphene thin film. The maximum output power was 4.5 mW and the single pulse energy was 85 nJ at 53 kHz repetition rate, and the pulse width was about 1.4 μs. The pulse width and the repetition rate of the Q-switched fiber laser can be changed along with the pump power. To the best of our knowledge, this is the first report of graphene saturable absorber for passively Q-switched 2 μm fiber lasers.     

High power room-temperature design of terahertz quantum cascade laser based on difference frequency generation

Terahertz (THz) quantum cascade lasers (QCLs) are key elements for high-power terahertz beam generation for integrated applications. In this study, we design a highly nonlinear THz-QCL active region in order to increase the output power of the device especially at lower THz frequencies based on difference frequency generation (DFG) process. It has been shown that the output power increases for a 3.2 THz structure up to 1.2 μW at room temperature in comparison with the reported power of P = 0.3 μW in [1]. The mid-IR wavelengths associated with this laser are λ₁ = 12.12 μm and λ₂ = 13.93 μm, which are mixed in a medium with high second-order nonlinearity. A similar approach has been used to design an active region with THz frequency of 1.8 THz. The output power of this structure reaches to 1 μW at room temperature where the mid-IR wavelengths are λ₁ = 12.05 μm, λ₂ = 12.99 μm.