Compact resonantly intra-cavity pumped tunable Ho:Sc2SiO5 laser

A compact intra-cavity pumped low threshold continuous-wave Ho:Sc₂SiO₅ laser is reported. The characteristics of output wavelength tuning are investigated by use a intra-cavity briefringent (BF) filter. A wavelength tunable range of 140 nm from 2020 to 2160 nm is achieved. For the free-running mode, the laser slope efficiency is 24.8%, when the output central wavelength is 2110 nm. The laser threshold is about 820 mW of incident pump power. With the BF filter, a maximum output power of 870 mW is obtained at the incident pump power of 5 W, corresponding to a slope efficiency of 20.3%. The characteristics of output wavelength verse the crystal temperature are also investigated.     

Continuous-wave 560 nm light generated by intracavity SrWO4 Raman and KTP sum-frequency mixing

An LD end-pumped Nd:YAG/SrWO₄ continuous-wave 560 nm laser is presented based on intracavity sum-frequency mixing of the fundamental and first-Strokes light. The maximum output power of 330 mW at 559.6 nm was obtained for the diode pump power of 13.7 W and the conversion efficiency was about 2.5%. The intense blue emission was also observed in the SrWO₄ crystal when the Raman laser was operating above threshold. This blue emission is centered at 473 nm, which also happened to YVO₄.     

A 980 nm Yb-doped single-mode fiber laser pumped by a 946 nm Q-switched Nd:YAG laser

We demonstrate a 980 nm single-mode Yb-doped fiber laser with a 946 nm Q-switched Nd:YAG laser used as the pump source. The experimental arrangement exploited a 36.5 cm length of fiber and used the output from both ends of the cavity, providing a total average output power of 100 mW with a slope efficiency of 38%. In order to increase the coupling efficiency and the practicability of the fiber laser, another experimental setup with single ended output was studied, producing an average output power of 80 mW from a fiber length of 23.5 cm. The pulse duration is 10 ns at a repetition frequency of 16 kHz. The linewidth of the laser is 4 nm, ranging from 977 to 981 nm.     

High index contrast Er:Ta2O5 waveguide amplifier on oxidised silicon

We report a high index contrast erbium doped tantalum pentoxide waveguide amplifier. 2.3 cm long waveguides with erbium concentration of 2.7 × 10²⁰ cm^? 3 were fabricated by magnetron sputtering of Er-doped tantalum pentoxide on oxidised silicon substrates and Ar-ion milling with photolithographically defined mask. A net on-chip optical gain of ~ 2.25 dB/cm at 1531.5 nm was achieved with 20 mW of pump power at 977 nm launched into the waveguide. The pump threshold for transparency was 4.5 mW.     

Low-threshold, 12-MHz, multipass-cavity femtosecond Cr4+: Forsterite laser

We report on the development of an extended-cavity, low-threshold femtosecond Cr⁴⁺:forsterite laser operating near 1270 nm. The resonator was end-pumped by a continuous-wave Yb-fiber laser at 1060 nm. The 195-MHz short cavity could be operated with absorbed threshold pump powers as low as about 300 mW. To scale up the pulse energy, the cavity length was increased by using a q-preserving multipass cavity (MPC) consisting of a flat and a curved (R = 4 m), notched high-reflector. Kerr-lens mode locking was used to generate femtosecond pulses and double-chirped mirrors were included in the cavity for dispersion compensation. With an absorbed pump power of 1250 mW, the mode-locked laser produced 4 nJ of pulse energy at an average output power of only 47 mW. The corresponding repetition rate of the extended cavity was 11.7 MHz. The pulse-width was 90 fs and the spectral bandwidth was 23 nm, corresponding to a time-bandwidth product of 0.37.     

High-power tunable Er,Yb ribbon fiber laser

A high-power Er,Yb double-clad ribbon fiber laser pumped by a 9-diode-bar pump module is reported. The laser yielded 102 W of continuous-wave output at 1566 nm for a launched pump power of 244 W, corresponding to a slope efficiency of ~ 44% with respect to launched pump power. Tunable operation was achieved using a simple external feedback cavity with a diffraction grating and the operating wavelength could be tuned from 1533 nm to 1567 nm. Temperature distribution in the ribbon fiber geometry and prospects of power scaling will be discussed.     

330 MHz,sub 50 fs Yb: Fiber ring laser

We demonstrate 330 MHz repetition rate operation in a ring cavity Yb:fiber laser with an innovative wavelength-division-multiplexing collimator to raise the repetition rate. The spectral bandwidth of the pulse is 30 nm and the dechirped pulse width is 48 fs. The output power is 70 mW with 600 mW, 975 nm pump laser diode.     

Spectroscopy and efficient laser emission of Yb3+: LuAG single crystal grown by μ-PD

A LuAG shaped rod crystal, doped with Yb³⁺, has been grown by μ-PD technique. The crystal diameter was about 3 mm and the length around 130 mm. A complete spectroscopic investigation in the temperature range 10–300 K is reported and data has been utilized to model the laser behavior. In the laser experiment the Yb:LuAG sample was placed in an X cavity and pumped longitudinally obtaining an efficient CW laser emission. The Yb:LuAG laser yielded a maximum output power of 23 mW with a slope efficiency of 32% and a threshold around 35 mW, at lasing wavelength of 1030 nm. No significant depolarization effects were observed, indicating a crystal growth with negligible stress. The output beam profile was investigated, yielding M² ≈ 1.0 in both directions, further confirming the good optical quality of the sample.     

2 μm passive Q-switched mode-locked Tm3+:YAP laser with single-walled carbon nanotube absorber

We report the first demonstration, to our knowledge, of passive Q-switched mode-locking in a Tm³⁺:YAP laser, operating in the 2 μm broadly spectral region formed with a compact Z-flod cavity. A transmission-type single-walled carbon nanotube saturable absorber (SWCNT–SA) is used for the initiation of the pulse generation. The repetition rate of the Q-switched envelope was 60 kHz at the pump power of 8.6 W. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of ～92 MHz. A maximum average output power of 761 mW was obtained. The dependence of the operational parameters on the pump power was also investigated experimentally.     

Laser diode end-pumped passively Q-switched Tm,Ho:YLF laser with Cr:ZnS as a saturable absorber

Output performance of a continuous-wave (CW) laser diode end-pumped passively Q-switched Tm,Ho:YLF laser is demonstrated with a Cr:ZnS crystal as the saturable absorber. We particularly investigate the influence of saturable absorber's position in the resonator when the Cr:ZnS crystal is placed close to and far from the laser beam waist. We compare the experimental results at the two different positions, and find that the laser shows unusual output characteristics when the Cr:ZnS saturable absorber is placed close to the beam waist. The pulse width and the pulse energy almost keep constant, measured about 1.25 μs and 4 μJ respectively, when the pump power is changed in the range of 1–1.9 W. Moreover, the pulse repetition frequency can be tuned between 1.3 kHz and 2.6 kHz by changing the pump power. The output wavelength of the passively Q-switched laser shifts to 2053 nm from 2067 nm in CW operation.     

Efficient cw violet-light generation in a ring cavity with a periodically poled KTP

In this work, we experimentally demonstrate an efficient cw second harmonic generation (SHG) at 780 nm wavelength with a first-order type-I phase matching periodically poled KTP (PPKTP) crystal in a ring cavity, the wavelength corresponds to the D₂ line of Rb atom transition. The fundamental laser used is a grating-stabilized external cavity diode laser and its frequency is precisely locked to Rb atom transition frequency using the saturated absorption technique. About maximal 6.9 mW UV radiation of 390 nm with a net conversion of 9.5% at an input mode-matched power of 73 mW is generated with one crystal, and about maximal 8.8 mW with the net conversion of 12% is obtained with another crystal; the powers in stable operation are about 1.7 mW and 3.4 mW, respectively. This is, to our best knowledge, the first SHG experiment at 780 nm wavelength with the PPKTP in a ring cavity.     

Nanosecond-pulsed erbium-doped fiber lasers with graphene saturable absorber

We demonstrate graphene mode-locked nanosecond erbium-doped fiber laser in an all-fiber ring cavity. The clean and robust pulse train was generated at 27 mW pump power. Resultant central wavelength, repetition rate and pulse width was 1560 nm, 388 kHz and 6 ns, respectively. With two stage fiber amplifier, the output power was 553 mW, corresponding to single pulse energy of 1.4 μJ. In addition, the pulse-width can be varied ranging from 3 ns to 20 ns at repetition rate between 200 kHz and 1.54 MHz by changing the length of the laser cavity.     

Generation of tunable and narrow linewidth continuous-wave yellow laser by sum–frequency mixing of diode-pumped solid-state Nd:YAG ring lasers

We report a tunable, narrow linewidth and high beam quality continuous-wave (CW) yellow laser system at 589 nm. The system is an all solid-state design employing single-pass sum–frequency generation in a KTP crystal by mixing the 1064 nm with 1319 nm lines of two side-pumped Nd:YAG enforcing unidirectional ring lasers. With this method, a CW yellow laser at 589.159 nm with an output power of 0.8 W, a linewidth less than 1.5 GHz and a beam quality M² = 1.29 is obtained. The wavelength of the laser also can be precisely tuned from 589.112 to 589.181 nm in step-length of about 0.22 pm.     

Femtosecond single-mode diode-pumped Cr:LiSAF laser mode-locked with single-walled carbon nanotubes

A low threshold Cr:LiSAF laser pumped with an inexpensive single-mode laser diode emitting 120 mW was passively mode-locked with a novel ultrafast saturable absorber mirror based on single-walled carbon nanotubes (SWCNT-SAM). Pulses as short as 122 fs were achieved, tunable across 14 nm. A second pump diode coupled in polarization allowed to shorten the pulse duration to 106 fs, with up to 24-mW output power.     

Low-cost low-threshold diode end-pumped Tm:YAG laser at 2.016?μm

We report a low-threshold continuous-wave Tm:YAG laser that can be excited near 785?nm with low-cost, single-mode AlGaAs laser diodes. Low-threshold operation was achieved using a tightly focused, astigmatically compensated x-cavity containing a 2-mm-thick Tm:YAG crystal with 5?% Tm³⁺ concentration. Two linearly polarized single-mode diodes operating at 785.8?nm were polarization coupled to end pump the resonator. With a 6?% output coupler, as high as 32?mW of output power could be obtained at 2016?nm with 184?mW of incident pump power. The output could be further tuned in the 1935?C2035?nm range. Slope efficiency measurements indicated that cross-relaxation was very effective at this doping level. With a 2?% output coupler, lasing could be obtained with as low as 32.3?mW of pump power. In the limit of vanishing output coupling, the incident threshold pump power could be reduced to as low as 25?mW. To our knowledge, this is among the lowest lasing thresholds reported to date for continuous-wave, room-temperature thulium lasers.     

Cascaded continuous-wave singly resonant optical parametric oscillator pumped by a single-frequency fiber laser

We present a cascaded continuous-wave singly resonant optical parametric oscillator (SRO) delivering idler output in mid-IR and terahertz frequency range. The SRO was pumped by an ytterbium-doped fiber laser with 27 W linear polarization pump powers, and based on periodically poled MgO:LiNbO₃ crystal (PPMgLN) in two-mirror linear cavity. The PPMgLN is 50 mm long with 29.5 μm period. The idler power output at 3811 nm was obtained 2.6 W. The additional spectral components that have been attributed to cascaded optical parametric processes are described at increasing pump levels. Besides the initial signal component at about 1476.8 nm, further generated wavelengths with frequency shifts about 47 cm^?1, 94 cm^?1 and 104 cm^?1 were observed. It was speculated that the idler waves lie in the terahertz (THz) domain from the observed results.     

Cr4+:YAG passively Q-switched c-cut Nd:YVO4 self-Raman laser at 1168.6 nm

We demonstrate the first Cr⁴⁺:YAG passively Q-switched c-cut Nd:YVO₄ self-Raman laser at 1168.6 nm based on the Stokes shift of 816 cm⁻¹. At the pump power of 4.7 W, the maximum output power of the Stokes line at 1168.6 nm is 270.5 mW, corresponding to an optical conversion efficiency of 5.8%. The pulse width, pulse repetition rate, pulse energy and peak power are 8.8 ns, 35.8 kHz, 7.6 μJ and 0.86 kW, respectively. At the pump of 5.0 W, the Stokes line at 1097.2 nm based on Raman shift of 259 cm⁻¹ also appears.     

Influences of geometry parameter on mode suppression ratio of fiber grating external cavity semiconductor laser

According to equivalent external cavity approximation model, after taking into account the joint contribution of semiconductor laser, external cavity and fiber grating (FG) to the phase condition, the mode distribution of the fiber grating external cavity semiconductor laser (FGESL) can be determined. As a result, the effect of the FG external cavity length (L) on the side mode suppression ratio (SMSR) of the FGESL is investigated theoretically. The results show that with the injected current and the coupling efficiency increase of the SMSR has taken on rise at all. For strong feedback (R₂ = 10^?4), the SMSR become more flattened with more than 40 dB, but, for weak feedback condition, The SMSR have lesser than 35 dB by an oscillation during rising course. Under the condition of short external cavity, the SMSR is in deep relation to the external cavity length, but the SMSR of longer external cavity is smaller than the SMSR of shorter external cavity on the whole and for 8–11 mm of the external cavity length, the SMSR of the FGESL has better (SMSR > 40.8 dB), and the SMSR become more flattened.     

Switchable different operation states in an erbium-doped fiber laser cavity with normal dispersion

We demonstrate different operation states which can be switched by the polarization control in an erbium-doped fiber laser cavity with normal dispersion, including passive single-pulse and multiple-pulse mode-locking, coherent pulse pattern, and passive Q-switching. The mode-locked single pulse has a smooth and broad rectangular-shaped spectrum. With increasing pump power, multiple pulses appear and finally six pulses are observed, where the pulses have no interaction with each other. Keeping the pump power at 407 mW and adjusting the polarization state, we observe the coherent pulse pattern with the pulse numbers from 2 to 5. It is the first time five coherent pulses in the 1.55 μm normal dispersion cavity have been observed, to our knowledge. The mode-locked spectra are highly modulated and the largest pulse separation of 31.9 ps is observed for the two-pulse case. When the pump power exceeds 180 mW, the mode-locked operation can be switched to the passively Q-switched operation by controlling the polarization state. The repetition rate and pulse width can be changed by pump power variation, and the spectrum is tunable in the range of 8.45 nm.     

Modeling of laser-diode side-pumped continuous wave Nd:YAG/KTP green laser

By reasonably assuming the distribution of the pump light in laser medium, the equations about the absorption and the gain for the end-pumped lasers are applied to the side-pumped ones, and a theoretical model for laser-diode side-pumped continuous wave intracavity-frequency-doubling lasers is given, in which the thermally induced diffraction loss and the variation of the fundamental wave radii with the pump power are considered. By using a Z-type cavity, a laser-diode side-pumped continuous wave Nd:YAG/KTP green laser is realized. The threshold pump power is 15 W, and the highest output power of the green laser is 3.75 W at the pump power of 160 W, corresponding to an optical–optical slope efficiency 2.6%. The experimental results are consistent with the numerical solutions.