LD-pumped Novel All-solid-state Ultrafast Lasers Based On Ytterbium-doped Gain Media

The width of ultrafast laser ranges from picosecond (10-12s) to femtosecond (10-15s) level.Ultrashort pulsed lasers are widely used in commercially available systems of many fields,ranging from industrial processing, optical storage to medical and biological information andcommunication, which can be attributed to advantages of ultrashort pulse duration, high peakintensity, and broad spectrum and so on. With the improvement of laser diode (LD), LDpumped solid-state mode-locked lasers have become one of ideal ways to obtain ultrafastlasers. Gain medium is an indispensable component for laser generation, and its explorationcan be an opportunity for the development of solid-state mode-locked lasers. Yb3+doped lasercrystals, which are suitable for being LD pumped, have become one of the main media toobtain ultrashort pulses. Substrates of Yb3+doped laser crystals mainly include borate, silicate,garnet crystals and fluoride. From the perspective of experimental condition and researchvalue of the crystal, we selected Yb:Y2SiO5、Yb:CaF2–SrF2and Yb,Y:CaF2crystals withrepresentative and excellent properties and studied their performances of LD pumped ultrafastlasers. The following is the main content of this article:1. We reviewed the advantages and developments of all solid state lasers, ultrafast lasersand ytterbium doped lasers. We analyzed the basic principle and technique of passivemode-locking, and briefly described several saturable absorbers used in the experiment.2. Based on graphene oxide saturable absorber, the performances of LD-pumpedfemtosecond mode-locked Yb:Y2SiO5laser were studied. We briefly introduced thefabrication and characteristics of graphene oxide saturable absorber, and demonstrated theYb:Y2SiO5femtosecond laser with it for the first time. With inserting SF10prisms fornegative dispersion component, the laser produced stable trains with pulse duration of763fs at1059nm.Theaverageoutputpowerachieved700mW.3. With graphene saturable absorber, the performances of LD-pumped ultrafastmode-locked Yb:Y2SiO5laser were studied. We introduced the fabrication and characteristicsof graphene-SA with sandwich structure; using graphene absorber with high quality, weobtained the Yb:Y2SiO5mode-locked laser for the first time. Without dispersion element, theshortest pulse duration was~883fs at1042.6nm with an output power of1.013W. It is worthmentioning that without dispersion compensating element, this is the shortest Yb:Y2SiO5laser pulse.4. We demonstrated LD-pumped femtosecond mode-locked Yb:Y2SiO5laser. Withinserting SF10prisms, the Yb:CaF2–SrF2mode-locked laser was obtained using SESAM asabsorber. The shortest pulse duration was~634fs. This is the shortest pulse laser based onYb:CaF2–SrF2mixed crystal.5. The continuous wave (CW) and mode locked (ML) laser operations of Yb,Y:CaF2crystals were studied. We analyzed spectroscopic properties of several different dopedconcentration of Yb,Y:CaF2crystals. For the first time to our knowledge, the continuous waveoperation was obtained with the average output power of1.48W, corresponding to the opticalslope efficiency of31.3%. A passively mode locked laser based on a5at.%Yb,5at.%Y:CaF2crystal was demonstrated. The shortest pulse with duration of1.3ps was obtained usingSESAM at1051nm. The average output power achieved514mW under the absorbed pumppower of6.43W. The repetition frequency was60MHz.6. Using graphene as a saturable absorber, we realized the Yb,Y:CaF2crystalmode-locked laser for the first time. The laser produced stable trains with pulse duration of4.8psat1051nm.Theaverageoutputpowerwas370mW.