We demonstrated continuous-wave dual-wavelength operation of a Yb:YAP laser with intracavity birefringent element. The laser produced a wide range of wavelength pairs with spectral separation from 1 nm up to 35 nm. The average output power reached up to 800 mW. Dual-wavelength radiation was generated owing to the broad gain bandwidth of the Yb:YAP crystal and custom design of a birefringent filter.
Dual-wavelength operation of a diode-pumped Yb:YAP laser using a 1 mm-thick birefringent filter was demonstrated. Multiple wavelength pairs with wavelength separation ranging from 1.8 nm up to 11.3 nm could be generated. The gain balancing for oscillating wavelength pairs was based on the differential loss around a single transmission peak of the filter. In this regime of operation, separation of the wavelength pairs was not limited to the free-spectral range of the filter. This laser can be used to generate THz radiation using a photomixing technique.
We demonstrated continuous-wave dual-wavelength operation of a Nd:CALGO laser with intracavity conerefringent element. The laser produced conically refracted dual-wavelength radiation output with more than 100 mW of power. Dual-wavelength radiation was generated owing to the broad gain bandwidth of the Nd:CALGO crystal.
High power performance of diode-pumped Yb:YAP lasers with different crystal orientation (cuts) was investigated. The crystal samples exhibited similar pump absorption properties. In continuous-wave (CW) regime, the maximum output power of <7 W could be generated using the b-cut and c-cut Yb:YAP crystals with slope efficiency up to 70%, while the laser with the a-cut crystal was limited to 5.6 W of output power most likely due to the thermal lensing effect. Owing to the high thermal conductivity and broad emission bandwidth of Yb:YAP, this crystal is a suitable laser host for high power laser operation in CW and pulsed regimes.
Mode-locked lasers emitting ultrashort pulses in the 2-μm spectral range at high (100-MHz) repetition rates offer unique opportunities for time-resolved molecular spectroscopy and are interesting as pump/seed sources for parametric frequency down-conversion and as seeders of ultrafast regenerative laser amplifiers. Passively mode-locked lasers based on Tm3+- and Ho3+-doped bulk solid-state materials have been under development for about a decade. In 2009 we demonstrated the first steady-state operation of such a Tm:KLu(WO4)2 laser using a single-walled carbon nanotube (SWCNT) saturable absorber (SA), generating 10-ps pulses at 1.95 μm. In 2012 this laser produced 141-fs pulses at 2.037 μm. More recently, the study of numerous active media with different SAs resulted in the generation of sub-100-fs (sub-10-optical-cycle) pulses. Materials with broad and smooth spectral gain profile were selected, naturally emitting above 2 μm to avoid water vapor absorption/dispersion effects, including anisotropic materials, strong crystal-field distortion in hosts that do not contain rare-earths, crystals with structural or compositional (i.e. mixed compounds) disorder that exhibit inhomogeneous line broadening, mixed laser ceramics, and Tm,Ho-codoping of ordered and disordered crystals and ceramics. A broad absorption band in semiconducting SWCNTs spans from 1.6 to 2.1-μm whereas the absorption of graphene extends into the mid-IR and scales for multilayers, increasing the modulation depth. Compared to GaSb-based semiconductor SA mirrors (SESAMs), the carbon nanostructures exhibit broader spectral response and can be fabricated by simpler and inexpensive techniques. Chirped mirrors were implemented for groupvelocity dispersion compensation, to generate the shortest pulses, down to 52 fs at 2.015 μm.
High power performance of a continuous-wave Yb:YAP laser was investigated. The laser generated <7 W of output power with 22 W of pump power and slope efficiency of around 70% while maintaining high beam quality. The thermal lensing effect was observed at high pumping power. The combination of high thermal conductivity and broad gain bandwidth make this laser host a suitable candidate for high power CW and ultrashort pulse generation.
We demonstrated continuous-wave dual-wavelength (DW) operation of a Nd:CALGO laser using a single birefringent filter (BRF) plate. Owing to a new mechanism of the BRF loss action, the equal lasing thresholds at two wavelengths could be provided by a single transmission peak of the filter and wavelength separation was not limited to the free-spectral range (FSR) of the filter. A wide range of DW pairs with wavelength separation from sub-nm up to ~4 nm with adjustable spectral intensity ratio was experimentally demonstrated using a single 2 mm-thick BRF plate.
Monoclinic rare-earth silicates, RE2SiO5, are the promising hosts for Nd3+ doping. We have studied Nd:(Gd,Y)2SiO5, Nd:(Lu,Y)2SiO5 and Nd:Lu2SiO5 crystals for their suitability for ~1.3 μm (4F3/2 → 4I13/2) lasers. The absorption and stimulated-emission cross-section spectra were determined. The continuous-wave laser operation was studied in a compact plano-plano cavity. A b-cut Nd:(Gd,Y)2SiO5 crystal generated up to 0.75 W of linearly polarized emission at 1360.7 nm with a slope efficiency η of 16.9%. For the same crystal operated at the 4F3/2 → 4I11/2 transition, the output power reached 3.84 W at 1077.4 nm with η = 54.5% with a threshold of only 80 mW.
In this paper we present a passively mode-locked laser oscillator based on Yb:LPS crystal with a single-mode laser diode as a pumping source. The pulsed operation was initiated with a semiconductor saturable absorber mirror. The pulses were as short as 90 fs, which, to the best of our knowledge, is the shortest pulse duration obtained from a Yb:LPS laser to date. The central emission wavelength was 1050.6 nm and it was 16.2 nm broad. The average power was equal to 82 mW corresponding to a peak power of 7.8 kW.
Tetragonal calcium rare-earth aluminates, CaLnAlO4, are attractive laser host crystals. The emission of Nd3+ ions at 1.3- 1.4 μm due to the 4F3/2 → 4I13/2 transition is of interest for medicine, fiber optics, and light conversion. We report on compact Nd:CaLnAlO4 lasers using a plane-plane cavity. With an a-cut 0.8 at.% Nd:CaYAlO4 crystal diode-pumped at 802 nm, a maximum continuous-wave output power of 365 mW was achieved at 1.365 & 1.390 μm corresponding to the σ-polarization. The 4F3/2 → 4I13/2 laser performance of the Nd:CaLnAlO4 crystals was compared to that from a monoclinic Nd:KGd(WO4)2. At the 4F3/2→ 4I11/2 transition (1.08 μm), a Nd:CaYAlO4 micro-laser generated multi-watt output (>4 W) with a slope efficiency of 39%.
Fluoride-type crystals (CaF2, SrF2) doped with neodymium Nd3+ present interesting alternative as a laser active media for the diode-pumped mode-locked laser systems mainly because of their broad emission spectra as well as longer fluorescence lifetime in comparison with well-known materials as Nd:YAG or Nd:YVO4. In comparison with Nd:glass active material, SrF2 and CaF2 have better thermal conductivity. In spite of the thermal conductivity decreases with doping concentration, these crystal might be interesting alternative for the Nd:glass mode-locked laser systems. In this contribution we present the first results of the Nd,Y:SrF2 mode-locked laser diode-pumped at 796nm. Mode-locking operation using SESAM was successfully achieved in the pulsed pumping regime (pulse-duration 1.5 ms, frequency 10 Hz) with the overall average output power of 2.3 mW (corresponding to the power amplitude of 153 mW) in one output beam at the wavelength of ~1055 nm. The actual pulse-duration was 87 ps.
In this contribution we present spectroscopic and laser properties of TGT (temperature gradient technique) grown
Nd,Y:SrF2 crystals with neodymium concentration of 0.4, 0.65 and 0.8 at.%. The absorption cross-section, fluorescence spectra and fluorescence decay time were measured. For the laser experiments, the noncoated crystal samples 3.5 or 5 mm thick were pumped by a 796 nm laser diode matching the Nd:SrF2 absorption peak. Several output couplers with
reflectivity ranging from 70 to 98 % at the generated wavelength were tested. In the pulsed pumping regime (pulseduration
2 ms, frequency 10 Hz), the maximum average output power of 75 mW was obtained with the slope efficiency
as high as 48 % and the optical-to-optical efficiency of 42 % with respect to the absorbed pump power. The output beam
spatial profile was nearly Gaussian in both axes, oscillations started at the wavelength of 1057 nm. At higher pumping
levels, the second emission line at 1050 nm appears corresponding to our fluorescence measurements. Wavelength
tuning using birefringent filter from 1048 to 1070 nm is probably given by crystal-field splitting of the 4F3/2 manifold in Nd3+. True-CW laser operation was also successfully obtained at lower pumping level with the maximum output power of 90 mW using output coupler reflectivity of 98 %.
The cross-orbit scanning is very important for Fresnel telescope synthetic aperture imaging ladar system. This paper presents a design of large-angle high speed scanner based on electro-optic crystal for the cross-orbit scanning in Fresnel telescope synthetic aperture imaging ladar system. The designed scanner is based on the space-charge-controlled EO effect in KTN. In the experiment the crystal temperature should be kept a little higher above Tc to obtain a large EO effect and the polarization of the laser beam should be parallel to the direction of the driving electric field. Compared with other conventional EO crystal scanner, the new scanner can greatly improve the scanner angle by several times when maintains high speed and accuracy, which will have a great potential for cross-orbit scanning applications in Fresnel telescope synthetic aperture imaging ladar system.
We present first experimental investigations on Ytterbium-doped Sc2SiO5 as a promising gain medium for thin-disk
lasers. This oxyorthosilicate laser material combines good thermo-mechanical properties and a broad emission
bandwidth suitable for high-power cw and mode-locked laser operation. The demonstrated average output powers of up
to 75 W with a not yet optimized thin-disk crystal confirm the power capability of this new material and preliminary tests
on passive mode-locking indicate the high potential for future ultrafast thin-disk laser oscillators.
Diode-pumped soliton and non-soliton mode-locked Yb:(Gd1-xYx) 2SiO5 (x=0.5) lasers have been demonstrated together
for the first time to the author's knowledge. For the non-soliton mode locking, output power could achieve ~1.2 W, and
pulse width was about 20ps. For the soliton mode-locked operation, the pulse width was 1.4ps at the wavelength of
1056nm and 375fs at the wavelength of 1042nm, with a pair of SF10 prisms as the negative dispersion elements. The
repetition rate was 48 MHz. The critical pulse energy in the soliton-mode locked operation against the Q-switched mode
locking was much lower than the value in non-soliton mode-locked operation.
We reports on a diode-pumped passively mode-locked Yb:SSO laser with a SESAM. Pulses
duration as short as ~2 ps with a repetition rate of 53 MHz were generated. The output power
achieved ~1.9 W at a pump power of 11.5 W.
A new alloyed crystal, Yb:LYSO, has been grown by the Czochralski method in our institute for the first time, and its
effective diode-pumped cw tunable laser action was demonstrated. The alloyed crystal retains excellent laser properties
of LSO with reduced growth cost, as well as the favorable growth properties of YSO. With a 5-at.% Yb:LYSO sample,
we achieved 2.84 W output power at 1085 nm and a slope efficiency of 63.5%. And its laser wavelength could be tuned
over a range broader than 80nm, from 1030nm to 1111 nm. This is the broadest tunable range achieved for Yb:LYSO
laser, as far as we know.
In this paper, the absorption and Fluorescence spectra of Cr4+,Nd3+:GGG (Cr,Nd:GGG) crystal, Nd:GGG crystal and Cr4+:GGG crystal are reported. In the absorption spectra there are big absorption bands at 400 and 520nm, which correspond to the 4A2→4T1 and 4A2→4T2 transitions. The luminescent spectra of Cr,Nd:GGG and Nd:GGG show that the luminescent center of Cr,Nd:GGG is at 1.062um, but the intensity is 6 times lower than that of Nd:GGG. The luminescent lifetimes of Cr,Nd:GGG is shorter than that of Nd:GGG. These may be caused by the existence of ground state absorption of Cr4+ which quenches the Nd3+ emission intensity. These Cr,Nd:GGG crystals may be potential materials for compact, efficient, high stability diode- laser-pumped passive Q-switched solid state laser.
Sapphire is widely used material for blue emitting diode, laser diode devices, visible-infrared window and radome applications. Although there is a large mismatch in the lattice constants and thermal expansion coefficient between nitride and sapphire, sapphire is still known as the most commonly used substrate in the GaN device for its physical robustness and high temperature stability. The ensuing component performance is highly dependent on the quality of the surface processing. In this work the effects of mechanical polishing, chemo-mechanical polishing (CMP) as well as CMP and subsequent chemical etching on the properties of sapphire substrate surfaces has been studied. The sapphire substrates have been investigated by means of polarizing microscopy, atomic force microscopy (AFM), X-ray diffraction rocking curves (XRCs) and micro-Raman spectroscopy. The results show that CMP with subsequent chemically etching yields the best quality sapphire substrate surfaces. The optimized conditions to realize good substrate and smoother surface morphology have been obtained.
We report on functional color centers and waveguide formed by using 800nm, 120fs, 200kHz pulse laser in alkali halide crystals such as KCl and LiF. These crystals are transparent in the wavelength ranging from 250-1000nm. After irradiated by the 800nm tightly focused femtosecond laser, the crystal changed to dark and color centers have been formed. Some of these color centers are useful and alkali halide crystal with these color centers is one type of laser crystal (color center laser crystal). And also photoinduced refractive index changes have been formed by focusing the laser beam.
Thin films of beta barium borate (β-BBO) have been prepared by liquid phase epitaxy on Sr2+-doped α-BBO (001) substrates. The thin films were characterized by X-ray diffraction and X-ray rocking curve. The results of X-ray diffraction indicate that the films show highly (00l) preferred orientation on (001)-oriented substrates. The full width at half-maximum of the rocking curve for the film is as low as 676.6 arcsec, which shows the high crystallinity of the thin film. The absorption edge of β-BBO on Sr2+-doped α-BBO substrate is 190 nm. The films show second harmonic generation of 400 nm light upon irradiation with 800 nm Ti: Sapphire femtosecond laser light. These results reveal the possibility of fabricating β-BBO (001) films on (001)-oriented Sr2+-doped α-BBO substrates by LPE.
The Mg-doped near stoichiometric LiNbO3 crystal of 30mm in diameter and 20mm in length was grown with top seed solution growth (TSSG) method from Li-rich melt doped with 1mol% MgO. Compared with nondoped congruent LiNbO3 crystal, fundamental absorption edge of the as-grown crystal shifted to shorter wavelength and position of the OH- infrared absorption peak also changed distinctly. All these results indicated that composition of the as-grown crystal was near-stoichiometric.
We investigated the operation of a diode-pumped Yb:YAG laser passively Q-switched, by Cr4+:YAG, Cr4+:LuAG, and Cr4+:GSGG saturable absorbers. The results presented here are focused towards the design of a passively Q-switched Yb:YAG microlaser. The free-running performance of both rod and a disk Yb:YAG is characterized, and experimental parameters such as gain and loss are evaluated. These values, together with the value of the stimulated emission cross section, e.g. (sigma) emequals3.3x10-20 cm2 were found to fit between our experimental results and an existing numerical model which relates the experimental and physical parameters to the minimal threshold pumping power. Q-switched pulses with maximum peak power of approximately equals 10.4-kW, and energy of approximately equals 0.5 mJ/pulse were extracted with 30% extraction efficiency.
During the last decade, Nd:YVO4 has been developed as a promising substitutes for Nd:YAG in diode-pumped lasers due to its high absorption and emission cross-sections. However, the applications of YVO4 are limited due to its poor physical- mechanical properties and growth difficulty etc. Now, in this present paper, we have developed the high-doped Nd:YAG(SUPER- Nd:YAG) crystals. It shows high absorption cross-section and has many advantages over Nd:YVO4: (1) Due to the cubic symmetry and high quality, Nd:YAG is easy to operate with TEM00 mode. (2) Nd:YAG can be Q-switched with Cr4+:YAG directly (sandwich). (3) Nd:YAG can produce blue laser with the frequency-doubling of 946 nm. (4) Nd:YAG can be operated in a very high power laser up to kW level.
In this paper, the absorption spectra characters of the (Cr, Yb): YAG, Cr:YAG and Yb:YAG crystals are reported. In the absorption spectra of the (Cr, Yb): YAG crystal, there are two absorption bands at 937 nm and 968 nm respectively, which are suitable for InGaAs diode laser pumping; and there is an absorption band of Cr4+ near 1030 nm, which is suitable for passive Q switch laser output at 1.03 micrometers . This Cr-Yb-codoped crystal may be a potential material for compact, efficient, high-stable diode laser pumped passive Q-switched solid-state laser.
We have successfully grown Yb:FAP(fluorapatite) crystal doped with 1 - 5 at% Yb by CZ technique. Crystalline boules which are colorless and transparent have the size of 22 mm in diameter and 45 mm in length. The optimal growth parameters are presented. During a Yb:FAP crystal growth run there exists a continuous loss of fluoride through evaporation, so 5% excess of calcium fluoride was usually added. To eliminate the defects, a post-annealing method has been developed where the boule is suspended above the melt surface for two days in a temperature zone that is about 400 degrees Celsius below the melting point. The defects of crystals were discussed, and the spectroscopy performances of Yb:FAP crystal were reported.
Different Raman spectra and lattice parameters of Mn5+-doped Ba3 (VO4) 2 and Ba3 (V1-xTax04) 2 (0 < x< 0.5) were described. The optical spectroscopy and lifetime of Mn5+ in Ba3 (V04) 2 and Ba3 (V1-xTax04) 2 were also presented and analyzed. It' s suggested that Mn5+ enters a relatively weaker field in Ba3 (V1-xTax04) 2.
In order to achieve large-sized and high-quality BaTiO3 crystals, a three-temperature-zone gradient transport technique has been developed. Samples of commercial BaTiO3 photorefractive crystals are routinely grown with dimensions of approximately 30 X 30 X 25 mm. Polished and poled cubes as large as 12 X 10 X 10 mm can be fabricated.
Cr3+:LiCaAlF6 single crystals were grown by vertical Bridgman method from stoichiometric composition melt on our growth apparatus which was simple and easily operated. Boules were grown unseedly firstly and then along [1010] at 1 mm/h in a following atmosphere of Ar. The micro-defects in Cr3+:LiCaAlF6 have been studied in detail with the help of x-ray diffraction, optical microscope, SEM, EDS and WDS. Heterogeneous micro-crystallites, inclusions of impurity particles and bubbles are found the main defects in the crystal. Traces of OH- are found in the boules by infrared spectroscopy. The absorption and emission spectra of Cr3+ in LiCaAlF6 are also presented.
Compared to other Nd3+ doped materials such as YAG:Nd3+, YAP:Nd3+, and YLF:Nd3+, crystal LaxNd1-xMgAl11O19 (LNA) has relatively much higher Nd concentration, long upper state lifetime, and large absorption bandwidths. LNA crystals have been pumped by laser diode arrays emitting around 800 nm. High-quality LNA crystals for this purpose have been grown.
The pulse width of a Q-switched diode laser pumped solid-state laser is compressed by the technique of gain switching for the first time. The experimental results are in agreement with the calculated values. Relations between pulse duration, peak power, and step jumping pump are discussed in detail.
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