Passive Mode Locking of a Diode-pumped Hybrid Nd:glass and Nd:YVO4 Lasers PDF Download

Author: Sukanya Tachatraiphop
Publisher:
ISBN:
Category : Mode-locked lasers
Languages : en
Pages : 324

View

Book Description

Author: Tanant Waritanant
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description
This work proposed to study Neodymium-doped laser crystals as an alternative for ultrashort pulse generation with medium output power level and high efficiency. The first section of this thesis focused on the thermal effect which is the main limitation in power scaling. The results showed that the thermal lensing effect is significantly reduced with in-band pumping at 914 nm. Aside from thermal lens effect investigation, discrete wavelength tuning and dual-wavelength operations were demonstrated with intracavity birefringent plates. Mode locking operations with SESAM as saturable absorber was demonstrated under 914 nm pump wavelength for the first time with the highest efficiency to date. The output in mode-locked regime was stable and self-starting with 16 ps pulse duration which can be extended to adjacent emission lines at 1073 nm and 1085 nm. Finally, two important candidates for low quantum defect pumping, Nd:CALYO and Nd:SYSO, were identified and tested for the first time.

Author: Louis McDonagh
Publisher: Cuvillier Verlag
ISBN: 3736930283
Category : Science
Languages : en
Pages : 180

View

Book Description
For the last decade, neodymium-doped orthovanadate has established itself as the active material of choice for commercial solid-state lasers emitting in the 1 µm range, with output powers from several hundred milliwatts to a few tens of watts, in continuous-wave, short nanosecond Q-switched, or picosecond modelocked pulsed regimes. Its main advantages over other Nd-doped hosts such as YAG are a large stimulated-emission cross section leading to a high gain, a strong pump absorption allowing the efficient mode-matching of tightly-focused pump light, and a natural birefringence resulting in a continuously polarized output. The main drawbacks, however, are rather poor mechanical characteristics and strong thermal lensing, effectively limiting the maximum applicable pump power before excessively strong and aberrated thermal lensing prevents an efficient operation in a diffraction-limited beam, and ultimately the crystal’s fracture. Put aside the power limitation, the association of vanadate with diode end pumping allows for the realization of highly efficient and reliable laser sources based on well-known technologies, which provides an advantage in terms of manufacturability and cost-effectiveness over other high-potential technologies such as disks and fibers. This thesis introduces a novel pumping technique for Nd:YVO4 that allows for the realization of significantly higher-power laser sources with a high optical-to-optical efficiency and diffraction-limited beam quality, while keeping the benefits of a well-established technology. It consists in pumping at a wavelength of 888 nm instead of the classic 808 nm, providing a low and isotropic absorption, which results in a smooth distribution of the absorbed pump light in long crystals, effectively limiting the deleterious effects of high inversion density such as crystal end-facet bulging, high crystal temperature, aberrated thermal lensing, and upconversion. After presenting vanadate’s spectroscopic and physical characteristics, a complete analysis of the heatgenerating effects is performed, allowing for side-by-side simulations of the thermal effects in practical 808 nm and 888 nm pumped systems, and for an evaluation of their respective thermal lensing behaviors. Continuous-wave operation was thoroughly investigated, first in a multi-transversal mode oscillator to assess the maximum optical efficiency with optimum pump-mode matching and the thermal lensing characteristics. A TEM00 resonator was then developed with a single crystal and one pump diode, providing 60 W of output power with an optical efficiency of 55% and a beam quality of M2 = 1.05. This resonator was symmetrically replicated to form a periodic resonator, providing 120 W of output with the same optical efficiency and beam quality. This two-crystal configuration was then modified to an oscillator-amplifier configuration, providing a single-pass extraction efficiency of 53% and a total oscillator-amplifier output of 117 W without any beam-quality degradation. Intracavity doubling of the one and two-crystal configurations was achieved by inserting a non-critically phase-matched LiB5O3 (LBO) non-linear crystal in the resonator, providing up to 62 W of diffraction-limited green light at 532 nm with low-noise characteristics thanks to a large number of oscillating modes, thus limiting the effects of the “green problem”. A strong industrial interest resides in Q-switched lasers emitting nanosecond pulses, particularly with a high average power, high pulse repetition rate, and pulse durations of a few to several tens of nanoseconds. Achieving high-frequency and short-pulse operation both require a high gain, which explains the domination of Nd:YVO4 over lower-gain materials such as Nd:YAG or Yb:YAG. Thus, an acousto-optically Q-switched oscillator was demonstrated with 50 W output power and 28 ns pulse duration at 50 kHz. Pulse duration, however, is inversely proportional to the pulse energy, so that an increase in repetition rate inevitably results in an almost linear increase in pulse width. A cavity-dumped Q-switched oscillator was built to circumvent this limitation, the pulse length being defined by the cavity roundtrip time and the electro-optic cell switching time. It provided a constant pulse duration of 6 ns up to a repetition rate of 100 kHz and a maximum output power of 47 W. Such short pulse durations are normally available with output powers of a few watts from Q-switched lasers, and conversely Q-switched lasers of similarly high output power deliver pulses of several tens to over 100 ns in duration. There exists another strong interest in high average power quasi-cw picosecond sources, which allow for the efficient generation of green and UV radiation, or even red-green-blue for laser video projection. Passive mode locking with a semiconductor saturable absorber mirror (SESAM) is the preferred technique employed for the stable and self-starting generation of picosecond pulse trains, yet a high gain is necessary for achieving high repetition rates while avoiding the Q-switched mode-locking regime. Thus SESAM mode locking was applied to an 888 nm pumped oscillator, achieving 57 W of output power at a repetition-rate of 110 MHz and a pulse duration of 33 ps. Its output was efficiently amplified in a single pass up to 111 W without any beam quality, temporal, or spectral degradation. The high peak power of 30 kW allowed for the generation of 87 W of second harmonic at 532 nm with an efficiency of 80%, and 35 W of 355 nm third harmonic with a conversion efficiency of 33% in LBO crystals. The wide range of high-power systems demonstrated in this work illustrate the benefits of the optimized pumping of Nd:YVO4 at 888 nm, maintaining its highly-desirable characteristics such as a high gain and a polarized output while extending its power capabilities far beyond regular 808 nm pumped systems. This improvement should allow Nd:YVO4 systems to compete with high-power technologies such as disks and fibers, which often struggle in the generation of short pulses because of their low gain and strong non-linear effects, respectively.

Author: Mohammad Nadimi
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description
The main obstacle in power scaling of the well-known Nd-doped lasers such as Nd:YVO4 is the thermal lensing effect. One of the proposed solutions to effectively alleviate this problem was based on the reduction of heating within the laser crystal. This was extensively investigated with the Nd:YVO4 crystal by pumping the laser at 914 nm instead of the standard pumping at 808 nm wavelength. In context of high power applications, the crystal of Nd:GdVO4 is an interesting alternative to the Nd:YVO4 as it offers the benefits of good spectral features (similar to Nd:YVO4) and much higher thermal conductivity. However, there is only one proof-of-principle work on continuous-wave (CW) Nd:GdVO4 laser using this pumping approach in which an output power of 3.35 W was reported. The full power scaling potential of the Nd:GdVO4 laser crystal to produce high output power has not been demonstrated to date. In this PhD thesis, I addressed this issue and investigated the high power operation of Nd:GdVO4 lasers under a new pumping wavelength of 912 nm. First, the thermal lensing behaviour of a 1063 nm Nd:GdVO4 was studied, both experimentally and by finite element analysis (FEA) method. The thermal lensing strength in Nd:GdVO4 laser under 912 nm pumping was significantly reduced when compared to the Nd:GdVO4 laser with 808 nm pumping or even Nd:YVO4 laser with 914 nm pumping. The next step of this research was focused on high power operation of Nd:GdVO4 lasers where we achieved 19.8 W of output power at 1063 nm. As a side work in the CW regime of operation, the possibility of discrete wavelength tuning and dual-wavelength operation of the Nd:GdVO4 laser were examined by using an intracavity birefringent filter. Discrete wavelength operation at four different wavelengths was demonstrated. Furthermore, for the first time we were able to demonstrate a dual-wavelength operation of the Nd:GdVO4 laser as a 1063 and 1071 nm wavelength pair. The last aspect of this PhD thesis was concentrated on generation of picosecond pulses. We were able to report on the first semiconductor saturable absorber mirror (SESAM) mode-locked (ML) Nd:GdVO4 laser with 912 nm pumping. The laser generated 10.14 W of average output power with the pulse width of 16 ps at the repetition rate of 85.2 MHz. To the best of our knowledge this is the highest average output power ever obtained from any of the SESAM mode-locked Nd-doped solid-state lasers that were pumped around 912 nm.

Author:
Publisher:
ISBN:
Category : Electrooptics
Languages : en
Pages : 670

View

Book Description

Author: Colin E. Webb
Publisher: CRC Press
ISBN: 9780750309639
Category : Technology & Engineering
Languages : en
Pages : 1282

View

Book Description

Author: Colin E. Webb
Publisher: CRC Press
ISBN: 9780750309608
Category : Technology & Engineering
Languages : en
Pages : 1294

View

Book Description

Author: Sukanya Tachatraiphop
Publisher:
ISBN:
Category :
Languages : en
Pages : 122

View

Book Description

Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 784

View

Book Description

Author: Md. Zubaer Eibna Halim
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description
Solid-state lasers are capable of providing versatile output characteristics with greater flexibility compared to other popular laser systems. Lasing action has been achieved in many hundreds of solid-state media, but Nd-ion doped gain media are widely used to reach high power levels with short pulses. In this work, commercially available Nd:KGW crystal served as a gain medium to achieve pulsed operation at 1067 nm. This laser crystal offers large stimulated emission crosssection and gain bandwidth which facilitates generation of high peak power pulses in the picosecond regime. The KGW crystal is monoclinic and biaxial in structure, and anisotropic in its optical and thermal properties. Due to poor thermal conductivity, this crystal can be operated within a limited power range before crystal fracture takes place. To reduce the amount of heat deposited in the gain media, we introduced a new pumping wavelength of 910 nm which reduces the quantum defect by more than 45%. Continuous-wave laser operation was optimized to operate in mode-locked regime. In order to achieve short light pulses from the continuous-wave laser, one of the end mirrors was replaced by a semiconductor saturable absorber mirror (SESAM) to generate 2.4 ps pulses at a repetition rate of 83.8 MHz. An average output power of 87 mW was obtained at lasing wavelength of 1067 nm and the beam was nearly diffraction limited with M^2 1.18. The peak power of the generated pulses was 427 W and energy of each pulse was 1 nJ. Pumping the crystal at longer wavelength (910 nm) reduced the thermal lensing of the crystal by half when compared to conventional pumping at shorter wavelength (808 nm). To the best of our knowledge, this is the first time passive mode-locking of a Nd:KGW laser was explored using the pump wavelength at 910 nm.