Microchip Lasers and Micro-Optics Technologies

Direct generation of higher-order Ince–Gaussian (IG) beams from laser-diode end-pumped Cr, Nd:YAG self-Q-switched microchip lasers was achieved with high efficiency and high repetition rate. An average output power of over 2 W was obtained at an absorbed pump power of 8.2 W; a corresponding optical-to-optical efficiency of 25% was achieved. Various IG modes with nanosecond pulse width and peak power of over 2 kW were obtained in laser-diode pumped Cr, Nd:YAG microchip lasers under different pump power levels by applying a tilted, large area pump beam. The effect of the inversion population distribution induced by the tilted pump beam and nonlinear absorption of Cr4+-ions for different pump power levels on the oscillation of higher-order IG modes in Cr, Nd:YAG microchip lasers is addressed. The higher-order IG mode oscillation has a great influence on the laser performance of Cr, Nd:YAG microchip lasers.

Highly efficient, laser-diode pumped Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers by bonding Yb:YAG crystal have been demonstrated for the first time to our best knowledge. The effect of transmission of output coupler (T(oc)) on the enhanced performance of Yb:YAG/Cr,Yb:YAG microchip lasers has been investigated and found that the best laser performance was achieved with T(oc) = 50%. Slope efficiency of over 38% was achieved. Average output power of 0.8 W was obtained at absorbed pump power of 2.5 W; corresponding optical-to-optical efficiency of 32% was obtained. Laser pulses with pulse width of 1.68 ns, pulse energy of 12.4 μJ, and peak power of 7.4 kW were obtained. The lasers oscillated in multi-longitudinal modes. The wide separation of longitudinal modes was attributed to the mode selection by combined etalon effect of Cr,Yb:YAG, Yb:YAG thin plates and output coupler. Stable periodical pulse trains at different pump power levels have been observed owing to the longitudinal modes coupling and competition.

Using a novel Q-Switching technique, we have produced 6-ns output pulses from a single-mode Nd:YAG microchip laser pumped with 120 mW of CW optical power. Rate-equation analysis indicates that with a pump power of 500 mW, Q-switched Nd:YAG microchip lasers having subnanosecond pulses and peak powers of several kilowatts are feasible. A small modification to the Q-switched microchip laser results in a polarization-switchable device. With such a device, we have switched the polarization of a microchip laser in under 5 μs, and theoretical modeling indicates that switching rates of several megahertz are possible.

>400W CW operation of a diode edge-pumped, composite all-ceramic Yb:YAG microchip (3mm- diameter core with a 200μm thickness) laser was successfully demonstrated. The M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> factor less than 7 up to 200 W CW was obtained.

414W CW operation of a diode edge-pumped, composite all-ceramic Yb:YAG microchip (a 3mm-diameter core with a 200µm thickness) laser was successfully demonstrated. The emission power density of 0.29MW/cm3 from the active volume is highest ever reported.

Here we report the characterization of the temporal jitter of a passively Q-switched Nd:YAG microchip laser. We experiment with different control schemes to reduce the observed jitter. Measurements were made for microchip laser temperatures from 10 degree(s) to 50 degree(s)C. The microchip laser was operated at various pulse rates from 500 Hz to 26 kHz.

Large topological charge optical vortex beams carrying orbital angular momentum have potential applications on optical trapping, optical communication with high capacity, quantum information processing. However, the beam quality is degraded in vortex beams generated with spiral phase plates or resonator mirrors with defect spots and optical conversion efficiency in solid-state lasers is sacrificed by controlling the loss of resonator. It is a big challenge for generating high beam quality, high-order cylindrical vector beams with large topological charge in compact solid-state lasers. Here, high-order cylindrical vector beams [Laguerre-Gaussian (LG) modes with zero degree and order of l, LG0,l] with tunable topological charges up to 14 have been generated in an annular beam pumped Yb:YAG microchip laser by manipulating the pump power-dependent population inversion distribution. Efficient performance with optical efficiency of 17.5% has been achieved. The output power is 1.36 W for a vector-vortex laser with 14 topological charges. The pump power dependent wavelength tunable and dual-wavelength laser oscillation in vector-vortex beams has been observed by controlling the reabsorption loss at 1030 nm. Wavelength tunable, dual-wavelength (1030 and 1050 nm) laser oscillation has been achieved for vector-vortex beams with topological charges of 8, 9, and 10. The laser beam quality factor M2 close to the theoretical value (l + 1) has been achieved for LG0,l vector-vortex beams with tunable topological charges up to 14. This work provides a new effective method for generating large topological charge high-order cylindrical vector beams in solid-state microchip lasers with high efficiency and high beam quality.

A theoretical model based on a quasi-four-level system is modified to investigate the effect of Yb concentration on performance of continuous-wave Yb:YAG microchip lasers by taking into account temperature-dependent thermal population distribution, temperature-dependent emission cross-section and concentration-dependent fluorescence lifetime, thermal loading, thermal conductivity, and thermal expansion coefficient. The local temperature rise in Yb:YAG crystal caused by the absorbed pump power plays an important role in the laser performance of Yb:YAG microchip lasers working at ambient temperature without actively cooling the sample. The output wavelengths dependent on output coupling, Yb concentration, and pump power level were analyzed quantitatively. The numerical simulation of Yb:YAG microchip lasers is in good agreement with experimental data. The optimized laser operation for Yb:YAG microchip lasers is proposed by varying the thickness and output coupling for different Yb concentrations. The effect of thermal lens, thermal deformation effect, and saturated inversion population distribution inside the Yb:YAG crystal on performance of heavy-doped Yb:YAG microchip lasers are also addressed.

Raman-gas filled HC-PCF has proved to be an outstanding Raman-convertor, as illustrated by the generation of more than 5 octaves wide Raman comb using a hydrogen-filled Kagome HC-PCF pumped with high power picosecond-laser, or the generation of multiline Raman-source in the UV-Vis using a very compact system pumped with micro-chip laser. Whilst these demonstrations are promising, a principal challenge for the industrialization of such a Raman source is its lifetime as the H2 diffusion through silica is high enough to leak out from the fiber within only a few months. Here, we report on a HC-PCF based Raman multiline source with a very long life-span. The system consists of hydrogen filled ultra-low loss HC-PCF contained in highly sealed box, coined CombBox, and pumped with a 532 nm micro-chip laser. This combination is a turnkey multiline Raman-source with a "shoe box" size. The CombBox is a robust and compact component that can be integrated and pumped with any common pulsed laser. When pumped with a 32 mW average power and 1 ns frequency-doubled Nd:Yag microchip laser, this Raman-source generates 24 lines spanning from 355 to 745 nm, and a peak power density per line of 260 mW/nm for the strongest lines. Both the output power and the spectrum remained constant over its monitoring duration of more than six months. The spectrum of this multiline laser superimposes with no less than 17 absorption peaks of fluorescent dyes from the Alexa Fluor family used as biological markers.

We have demonstrated a narrowband Littman configuration dye laser longitudinally pumped by the second harmonic of a 250 Hz pulse repetition frequency microchip laser with up to 50 microjoule pulse energies at 532 nm. Rhodamine 6Gd ye in methanol with a 5 cm cavity length produced 9 microjoule pulses with a slope efficiency of 20% at the peak intensity. The dye laser can be tuned from 550 to 575 nm. A 532 nm pump threshold below 4 microjoules was observed. Adding tunability to compact, economical microchip lasers with a spectrally narrow pulsed dye laser provides ideal characteristics for biotechnological applications.

High peak power, 355 nm ultraviolet (UV) short-pulse lasers are very useful for many applications, such as, materials processing and 3D printing. However, such applications are limited by the size and cost of UV lasers. We report the design and fabrication of a &lt; 6 MW peak power, very compact and cost-effective 355 nm UV microlaser. We used a specially designed Nd:YAG/ Cr4+:YAG microchip laser pumped through a fiber combiner. The in-house fabricated fiber combiner enabled a compact design using several low-cost/low-power, air-cooled laser diodes to pump the microchip laser, without sacrificing pump beam quality needed for end-pumping. The microchip laser used a [100]-cut Nd:YAG with an undoped YAG end-cap as the gain medium. This enabled high output power without depolarization, which is essential for high efficiency wavelength conversion. A low initial transmission Cr4+:YAG was used as the passive Q-switch to obtain high peak power. We achieved 11.3 mJ pulse energy, 935 ps pulse width, &lt;12 MW peak power with good beam quality at 1064 nm, without using a MOPA system. Third harmonic generation was performed by sum-frequency generation using Type I and Type II LBO crystals. We achieved 4.1 mJ pulse energy, 645 ps pulse width, resulting in 6.36 MW peak power at 355 nm. The conversion efficiency from 1064 nm to 355 nm was 52%. These are the highest pulse energy and peak powers achieved at 355 nm using a compact microchip laser. Our low-loss fiber combiner design for pumping is scalable, to further increase the output power.

We developed a tunable intracavity frequency-doubled Yb:YAG microchip laser and applied this tunable green laser to wavelength-multiplexed holographic memory. The tunable Yb:YAG green laser output a maximum power of 520 mW and a tuning range of 22.4 nm with single frequency. Moreover, we improved tuning range of fundamental oscillation and maximum tuning range of 84.5 nm (λ =1024.1~1108.6 nm) was obtained. Additionally, we investigate edge-pumped YbrYAG microchip lasers to achieve high power and brightness laser performances.

A diode-pumped Tm,Ho:KLu(WO4)2 microchip laser passively Q-switched with a Cr:ZnS saturable absorber generated an average output power of 131 mW at 2063.6 nm with a slope efficiency of 11% and a Q-switching conversion efficiency of 58%. The pulse characteristics were 14 ns/9 μJ at a pulse repetition frequency of 14.5 kHz. With higher modulation depth of the saturable absorber, 9 ns/10.4 μJ/8.2 kHz pulses were generated at 2061.1 nm, corresponding to a record peak power extracted from a passively Q-switched Tm,Ho laser of 1.15 kW. A theoretical model is presented, predicting the pulse energy and duration. The simulations are in good agreement with the experimental results.

Summary form only given. A point laser model for the simulation of generation of hybridly Q-switched solid-state microchip lasers with continuous diode pumping is proposed, taking into account the Stark splitting of the lasing levels into sublevels, excited state absorption in the passive Q-switches, the finite lifetimes of the both working laser levels and of the excited level of Cr/sup 4+/:YAG, fluctuations of spontaneous emission and pumping power, orientation of crystallographic axes of the saturable absorber in respect to the resonator partial polariser and so on.

All-fiber passively Q-switched fiber lasers have been demonstrated by using graphene oxide (GO) Q-switcher for possible applications in telecommunication, laser processing, fiber sensing and medical community. The GO material was obtained through a modified Hummers method from expanded acid washed graphite flakes and it was embedded into a polyvinyl alcohol (PVA) film to form a saturable absorber (SA) device. The Q-switched pulse operates at 1563.3 nm with a repetition rate that can be tuned from 44.33 kHz to 61.77 kHz as the pump power changes from 39 mW to 96 mW. The highest repetition rate of 61.77 kHz is achieved at a pump power of 96 mW and it is observed that the Q-switched pulse produced maximum pulse energy of 0.054 nJ and pulse width of 5.57 ?s at 96 mW pump power. Full Text: PDF ReferencesJ. Zayhowski and C. Dill, "Coupled-cavity electro-optically Q-switched Nd:YVO4 microchip lasers", Optics letters 20, 716 (1995). CrossRef C.-x. Gao, W. Zhao, Y.-s. Wang, S.-l. Zhu, G.-f. Chen, and Y.-g. Wang, "Passive Q-switched fiber laser with SESAM in ytterbium-doped double-clad fiber", 27th International congress on High-Speed Photography and Photonics, 62794G (2007). CrossRef M. Ahmed, N. Ali, Z. Salleh, A. Rahman, S. Harun, M. Manaf, "Q-switched erbium doped fiber laser based on single and multiple walled carbon nanotubes embedded in polyethylene oxide film as saturable absorber", Optics &amp; Laser Technology 65, 25 (2015). CrossRef S. Harun, M. Ismail, F. Ahmad, M. Ismail, R. Nor, N. Zulkepely, et al., "A Q-switched erbium-doped fiber laser with a carbon nanotube based saturable absorber", Chinese Physics Letters 29, 114202 (2012). CrossRef A. Martinez and Z. Sun, "Nanotube and graphene saturable absorbers for fibre lasers", Nat Photon 7, 842 (2013). CrossRef J. Boguslawski, J. Sotor, G. Sobon, R. Kozinski, K. Librant, M. Aksienionek, et al., "Graphene oxide paper as a saturable absorber for Er- and Tm-doped fiber lasers", Photonics Research 3, 119 (2015). CrossRef H. Ahmad, F. D. Muhammad, M. Z. Zulkifli, and S. W. Harun, "Q-switched pulse generation from an all-f iber distributed Bragg reflector laser using graphene as saturable absorber", Chinese Optics Letters 11, 071401 (2013). CrossRef