Thermal Lens Effect Research Articles

大功率半导体激光器波导热透镜效应及对慢轴光束发散角的影响

大功率半导体激光器波导热透镜效应及对慢轴光束发散角的影响

Study of the field-sequential modulation of Nd:YVO4/MgO:PPLN based intra-cavity frequency doubling green laser

The field sequential modulation of a Nd:YVO4/MgO:PPLN intra-cavity, frequency doubling green laser was studied. The modulation frequency was set at 1 kHz and the duty cycle was changed from 20% to CW operation. It was shown that the quasi-phase matched (QPM) temperature decreases with an increase of the modulation duty cycle, and in turn causing the peak efficiency to rise. It was found that the temperature change in MgO:PPLN and the thermal lens effect in Nd:YVO4 crystal were the respective origins of these observed experimental phenomena.

Thermal lens effect and fluorescence of motor oil investigated by holographic method

This paper presents studies of the thermal lens effect in the volume of motor oil by holographic methods using excitation of 447[Formula: see text]nm laser wavelength. The possibility of using a hologram of initial object, as a diffractive element, for obtaining the spectral dependence of the fluorescence of the oil product was shown.

Exploiting birefringent thermal lensing effect to manipulate polarization states of an Nd:YVO_4 self-mode-locked laser

An Nd:YVO4 laser with a convex-plano cavity is systematically studied to demonstrate the manipulation of output polarization state by using the birefringent thermal lensing effect of the gain crystal. Based on the theoretical analysis of the cavity stability under the influence of thermal lens, the polarization state of output emission is experimentally confirmed that can be controlled to switch from pure π- to pure σ-polarization by simply varying the pump focus position from the tight-focusing to defocusing conditions. More importantly, it is found that there exists an adequate pump focus position within the switching region to lead the π- and σ-polarization to have balanced gain for achieving a stable self-mode-locked laser with orthogonally polarized components. Under the orthogonally polarized mode-locked operation, the pulse repetition rates are found to be 2.23 and 2.33 GHz for the π- and σ-polarization with pulse duration to be 16.1 and 15.1 ps, respectively.

Measurement of the Thermal Lens Effect of a Liquid Sample by Using a Michelson Interferometer

Measurement of the Thermal Lens Effect of a Liquid Sample by Using a Michelson Interferometer

Peak-power scaling of femtosecond Yb:Lu2O3 thin-disk lasers.

We present a high-peak-power SESAM-modelocked thin-disk laser (TDL) based on the gain material Yb-doped lutetia (Yb:Lu2O3), which exceeds a peak-power of 10 MW for the first time. We generate pulses as short as 534 fs with an average power of 90 W and a peak power of 10.1 MW, and in addition a peak power as high as 12.3 MW with 616-fs pulses and 82-W average power. The center lasing wavelength is 1033 nm and the pulse repetition rates are around 10 MHz. We discuss and explain the current limitations with numerical models, which show that the current peak power is limited in soliton modelocking by the interplay of the gain bandwidth and the induced absorption in the SESAM with subsequent thermal lensing effects. We use our numerical model which is validated by the current experimental results to discuss a possible road map to scale the peak power into the 100-MW regime and at the same time reduce the pulse duration further to sub-200 fs. We consider Yb:Lu2O3 as currently the most promising gain material for the combination of high peak power and short pulse duration in the thin-disk-laser geometry.

Stable solar-pumped TEM00-mode 1064 nm laser emission by a monolithic fused silica twisted light guide

Abstract To improve TEM 00 -mode solar-pumped laser output power stability, a monolithic fused silica twisted light guide was firstly produced and then combined with both a 2D-CPC (Compound Parabolic Concentrator) and a 2 V-shaped cavity to achieve uniform pumping along a 3 mm diameter, 50 mm length, 1.0 at.% Nd 3+ :YAG rod through an heliostat-parabolic mirror system. Based on both refractive and total internal reflection principles, the light guide provided an effective solution to both guiding and redistributing highly concentrated solar radiations. A near-Gaussian profile focal spot was transformed into a uniform rectangular-shaped light column, facilitating further pump light coupling into the long and thin laser rod within the 2 V-shaped pump cavity. Optimum pumping parameters and solar laser output powers were found through both ZEMAX© non-sequential ray-tracing and LASCAD© laser cavity analysis codes. The light guide reduced considerably the thermal lensing effects of the solar laser. 2.7 W continuous-wave TEM 00 -mode (M 2 ≤ 1.05) 1064 nm solar laser emission with 2.3 W/m 2 collection efficiency and, more importantly, with 1.7% stability was finally achieved, being significantly more stable than the previous TEM 00 -mode solar lasers.

Flash-lamp-pumped 4 J, 50 Hz Nd:YAG nanosecond laser system for mobile and transportable equipment

A simplified flash-lamp pumped high-average-power Nd:YAG nanosecond laser system based on a master oscillator power amplifier platform was developed toward outside laser remote sensing. The performance of the laser system was demonstrated, obtaining 4 J output pulse energy with a 50 Hz operating frequency. Thermal lens effects were compensated for by using only simple image relays and up to 97% of the laser energy could be contained in the focal spot. The developed laser system was constructed using only components suitable for operation under outside conditions.

Optical Dispersion, Permittivity Spectrum and Thermal-Lensing Effect in Nickel-Doped Zinc Sulfide Nanoparticles

In this paper, Ni-doped ZnS (ZnS:Ni2+) nanoparticles (NPs) have been prepared through a chemical method. The average size of the particle is 45 nm. Thin films of the particles have been prepared by using the spin-coating method. The linear and nonlinear optical properties of Ni-doped ZnS thin films and the colloidal solution of them have been studied widely. Using a precise numerical method, the refractive index curve (dispersion curve), absorption coefficient and optical permittivity of Ni-doped ZnS film have been obtained. Using these values, the absorption coefficient of the colloidal solution of Ni-doped ZnS particles has been simulated and compared with experimental results. Finally, using the z-scan method at low laser irradiation, the thermo-optical effect has been studied and the nonlinear refractive index due to this effect has been reported.

Near-near-infrared thermal lens spectroscopy to assess overtones and combination bands of sulfentrazone pesticide

Thermal lens spectroscopy (TLS) in the near-near-infrared region was used to explore the absorptions of overtones and combination bands of sulfentrazone (SFZ) herbicide diluted in methanol. This spectroscopic region was chosen in order to guarantee that only thermal lens effect is noted during the experimental procedure. The results showed that it was possible to detect very low concentrations (~2ng/μL) of SFZ in methanol by determining its thermal diffusivity or the absorption coefficient due to the 3ν(NH)+1δ(CH) combination band. This minimum SFZ concentration is the limit observed by chromatography method. The findings demonstrated that the TLS can be used for precise and accurate assessment of pesticides in ecosystems. Besides, the 3ν(NH)+1δ(CH) combination band at 960nm can be used as a marker for SFZ in methanol.

Low-cost nonlinear optics experiment for undergraduate instructional laboratory and lecture demonstration

This paper presents a simple and affordable experiment on the thermal lens effect, suitable for an undergraduate educational laboratory or as a tabletop demonstration in a lecture on nonlinear optics. Such an experiment exploits the formation of a lens in an absorbing medium illuminated by a laser beam with a Gaussian intensity profile. As an absorber, we use a commercial soy sauce, which exhibits a strong thermal lensing effect. Additionally, we show how to measure the radius of a Gaussian beam using the knife-edge method, and how to estimate the focal length of the induced thermal lens.

A 526 mJ Subnanosecond Pulsed Hybrid-Pumped Nd:YAG Laser

A hybrid-pumped Nd:YAG pulse laser with a double-pass two-rod configuration is presented. The focal length of offset lens is particularly studied to compensate for the thermal lens effect and depolarization. For input pulse energy of 141 μJ with pulse duration of 754 ps, the pulse laser system delivers 526 mJ pulse energy and 728 ps pulse width output at 10 Hz with pulse profile shape preservation. The energy stability of the laser pulse is less than 3%, and the beam quality factor is less than 2.26.

Diode-pumped orthogonally polarized self-mode-locked Nd:YLF lasers subject to gain competition and thermal lensing effect.

The stable condition for π-polarization emission in an a-cut Nd:YLF laser is numerical analyzed to find the critical pump power for generating the orthogonally polarized emission. With the numerical analysis, an orthogonally polarized SML lasers at wavelength of 1047 nm and 1053 nm is experimentally achieved in a simple concave-plano cavity without any additional optical element. It is experimentally observed that the polarization switching and coexistence was successfully demonstrated by introducing gain competition and anisotropic thermal lens effect. In the orthogonal polarization mode-locked operation, the pulse durations are found to be 19.1 and 18.8 ps for π- and σ-polarization with pulse repetition rates of 3.85 and 3.89 GHz, respectively.

Numerical Analysis of the Output Characteristics of an Intracavity Optical Parametric Oscillator with Thermal Lensing Effect

Numerical Analysis of the Output Characteristics of an Intracavity Optical Parametric Oscillator with Thermal Lensing Effect

Thermal lensing effects on lateral leakage in GaN-based vertical-cavity surface-emitting laser cavities.

Lateral leakage of light has been identified as a detrimental loss source in many suggested and experimentally realized GaN-based VCSELs. In the present work we include thermal effects to realistically account for the substantial Joule heating in these devices. In contrast to what could be expected from the previous results, the induced thermal lensing does not make antiguided cavities more positively guided, so that they approach the unguided regime with extremely high lateral leakage. Rather, thermal lensing strongly suppresses lateral leakage for both antiguided and guided cavities. This is explained in terms of lowered launch of power from the central part of the cavity and/or lower total internal reflection in the peripheral part; the former effect is active in all cavities whereas the latter only contributes to the very strongly reduced leakage in weakly antiguided cavities. Thermal lensing suppresses lateral leakage both for the fundamental and the first higher order mode, but a strong modal discrimination is still achieved for the antiguided cavities. Thus, strongly antiguided cavities could be used to achieve single-mode devices, but at the cost of slightly higher threshold gain and stronger temperature dependent performance characteristics.

Thermal Lens Temperature Scanning technique for evaluation of oxidative stability and time of transesterification during biodiesel synthesis

In this work, laser-induced Thermal Lens Temperature Scanning technique (TL-TS) is applied to evaluate oxidative stability and time of transesterification during biodiesel synthesis. Samples collected at different time intervals during the transesterification process of sunflower (SF) and soybean (SB) oils were submitted to fast oxidation through temperature scanning (between 22 and 190°C), and simultaneously measured with the TL-TS technique. Temperature dependence of Thermal Lens effect amplitude showed the occurrence of oxidation, with the onset (Tonset) changing with the transesterification stages from 149 to 169°C for sunflower and from 120 to 142°C for soybean samples. The characteristic evolution of Tonset with reaction duration was estimated to be ∼7min for sunflower and ∼10min for soybean samples. The thermal diffusivity values were shown to be sensitive to rapid changes at transition temperatures, which could be related to molecular ruptures. Additional measurements were performed with DSC, TG and FTIR, to validate the information obtained by the TL-TS technique. In conclusion, the results showed the TL-TS technique as a promising tool for oxidative stability evaluation and determination of both chosen working temperature and minimal time interval for the solution to reach an optimized transesterification stage, thus contributing for reduction of costs, quality control and consequently for certification of biodiesel fuels.

Thermal, defects, mechanical and spectral properties of Nd-doped GdNbO4 laser crystal

A Nd-doped GdNbO4 crystal was grown successfully by Czochralski method. Its monoclinic structure was determined by X-ray diffraction; the unit-cell parameters are a = 5.38 A, b = 11.09 A, c = 5.11 A, and β = 94.56°. The morphological defects of Nd:GdNbO4 crystal were investigated using the chemical etching with the phosphoric acid etchant. For a new crystal, the physical properties are of great importance. The hardness and density of Nd:GdNbO4 were investigated first. Thermal properties of Nd:GdNbO4, including thermal expansion coefficient and specific heat, were measured along a-, b-, and c-crystalline axes. Thermal properties indicate that the Nd:GdNbO4 pumped along c-axis can reduce the thermal lensing effect effectively. The specific heat is 0.53 J g−1 K−1 at 300 K, indicating a relatively high damage threshold of Nd:GdNbO4. The transmission and emission spectrum of Nd:GdNbO4 were measured, and the absorption peaks were assigned. The strongest emission peak of Nd:GdNbO4 is located at 1065.3 nm in the spectral range of 850–1420 nm excited by 808 nm laser. The refractive index of Nd:GdNbO4 was calculated with the transmission spectrum and fitted with Sellmeier equation. All these obtained results is of great significance for the further research of Nd:GdNbO4.

Finite Element Analysis of Thermal Effects in Diode End-Pumped Solid-State Lasers

Thermal effects are the main obstacle to getting high power and good beam quality in diode end-pumped solid-state lasers. In this work, a theoretical investigation of thermal effects in single and dual end-pumped solid-state lasers is carried out using finite element analysis (FEA) for a selected number of widely used laser producing materials, namely, Nd:YAG, Yb:YAG, and Nd:KGW. Crystals with different dimensions are also investigated both in single and in dual end-pumped configuration. Finally, the effect of using composite crystals on thermal lensing is investigated. An experiment to measure the thermal focal length for two different crystals was carried out and a comparison with FEA computed focal length of the thermal lens is made. In all cases studied in this work, results show clear effects of thermal lensing with some differences depending on crystal type, pump power, and size.

Low power laser induced NLO properties and optical limiting of an anthraquinone dye using Z–scan technique

The nonlinear optical (NLO) properties and optical limiting of an anthraquinone (Reactive blue 4) dye is studied in the low power regime utilizing a continuous wave (CW) diode laser at 635 nm with total power of 5 mW. The NLO parameters such as nonlinear index of refraction (n2) and nonlinear absorption coefficient (β) were determined respectively from closed (S = 0.4) and open (S = 1) aperture Z–scan technique. Self-defocusing and reverse saturable absorption are the nonlinear mechanisms were observed in the dye sample. The real and imaginary parts of the third-order nonlinear susceptibility (χ3) were estimated to be Re (χ3) = −2.12 × 10−5 esu and Im (χ3) = 1.85 × 10−6 esu. The optical limiting behaviors of reactive blue 4 dye at different concentrations were performed under experimental condition. Variation of transmitted laser spot size as a function of sample position at far field was also observed. The diffraction ring patterns were recorded in the present dye sample due to thermal lensing effect. With these experimental results the authors believed that, the dye investigated here is a potential material for NLO applications.

CW and Q-switched GGG/Er:Pr:GGG/GGG composite crystal laser at 2.7 µm

We report the continuous-wave (CW) and passively Q-switched laser operations of a GGG/Er:Pr:GGG/GGG composite crystal at about 2.7 µm. Owing to the alleviation of the thermal lensing effect, the CW laser with a maximum output power of 463 mW was obtained with a slope efficiency of 15.5%. Based on the broadband saturable absorption property, a graphene saturable absorber (SA) mirror was fabricated and employed for realizing the Q-switched mid-infrared laser. Under an absorbed pump power of 2.47 W, an average output power of 186 mW was generated with a slope efficiency of 12.3%. The pulse width and the repetition rate of the laser were 360 ns and 120.5 kHz, respectively. These results indicate that the Er:Pr:GGG crystal, with the relatively lower upper-level lifetime, shows great promise for generating a short pulsed 2.7 µm mid-infrared laser using the graphene SA.