High-power diode-end-pumped Nd:YVO4 laser: thermally induced fracture versus pump-wavelength sensitivity

We report two kinds of compact and efficient diode-end-pumped TEM₀₀ lasers with output power >25 W at ≈50 W of incident pump power. One laser consists of a single 0.3 at. % Nd:YVO₄ crystal in a V-type cavity, the other laser includes two 0.5 at. % Nd:YVO₄ crystals in a linear cavity. Experimental results show that lowering Nd³⁺ concentration can be beneficial in extending the fracture-limited pump power but it also increases the sensitivity of the pump wavelength due to the overlapping efficiency. Received: 19 February 2000 / Revised version: 30 May 2000 / Published online: 20 September 2000     

500 W Nd:YAG zigzag slab MOPA laser

A MOPA Nd:YAG laser with end-pumped zigzag slab architecture has been developed. 277 W laser output is obtained from the master-oscillator stage, corresponding to the average slope efficiency of 35.9% and the optical conversion efficiency of 34.6%, which emits the maximum power of 402 with 1163 W of pump power. Furthermore, the amplifier stage produces 505 W with the slope efficiency of 24% and the extraction efficiency of 25%. The beam quality is estimated as M _x ² ≈ 10, M _y ² ≈ 50 in the orthogonal directions respectively.     

CW diode pumping and FM mode locking of a Nd: KGW laser

We have demonstrated cw diode end pumping of Nd: KGW, a novel solid-state gain medium, with up to 30% conversion efficiency into near-TEM₀₀ (M² < 1.05) output at = 1.067 µm for a pump level of 2.7 W. The slope efficiency was limited by intracavity reflections to 36%; however, direct comparison to a similar Nd:YAG laser indicates the same intrinsic slope efficiency of 60%. FM mode locking of this laser at 200 MHz has produced 12 ps pulses (compared to 16 ps for Nd: YAG), although an intracavity etalon was required. Considerable reduction in pulse width is possible (the line width limit is 0.5 ps) but different techniques may be necessary. Spatial hole burning was evident in both the 120 GHz free-running spectrum and the etalon-limited mode-locked spectrum.     

High efficiency continuous-wave single-frequency Nd:YVO<Subscript>4</Subscript> ring laser under diode pumping at 880 nm

An efficient single-frequency continuous-wave Nd:YVO₄ ring laser pumped at 880 nm is presented. With compact four-mirror ring cavity and optical isolator, we obtained an output power of 14.56 W at 1064 nm, corresponding to a slope efficiency of 61.7% and an optical-to-optical efficiency of 58.4% with respect to the absorbed pump power. The stability of the output power was better than ±0.5% over two hours. At the same time, a beam quality factor of M ²≈1.2 was measured and the line width of the longitudinal mode was about 25 MHz. To the best of our knowledge, this is the highest slope efficiency and optical-to-optical efficiency in single-frequency Nd:YVO₄ ring laser.     

All solid-state continuous-wave Nd:YAG laser at 1319 and 659.5 nm under direct 885 nm pumping

The continuous-wave high efficiency laser emission of Nd:YAG at the fundamental wavelength of 1319 nm and its 659.5-nm second harmonic obtained by intracavity frequency doubling with an LBO nonlinear crystal is investigated under pumping by diode laser at 885 nm (on the ⁴ F _3/2 → ⁴ I _13/2 transition). An end-pumped Nd:YAG crystal yielded 9.1 W at 1319 nm of continuous-wave output power for 18.2 W of absorbed pump power. The slope efficiency with respect to the absorbed pump power is 0.55. Furthermore, 5.2 W 659.5 nm red light is acquired by frequency doubling, resulting in an optical-to-optical efficiency with respect to the absorbed pump power of 0.286. Comparative results obtained for the pump with diode laser at 808 nm (on the ⁴ F _5/2 → ⁴ I _13/2 transition) are given in order to prove the advantages of the 885 nm wavelength pumping.     

Diode-pumped continuous-wave Nd:YLF laser at 1313 nm

We present an efficiency Nd:LiYF₄ (Nd:YLF) laser operating at 1313 nm pumped directly into the emitting level ⁴ F _3/2. At the incident pump power of 10.3 W, as high as 3.1 W of continuous-wave output power at 1313 nm is achieved. The slope efficiency with respect to the incident pump power was 36.1%. To the best of our knowledge, this is the first demonstration of such a laser system. Comparative results obtained for the pump with diode laser at 806 nm, into the highly absorbing ⁴ F _5/2 level, are given in order to prove the advantages of the 880 nm wavelength pumping.     

Efficient continuous-wave 908 nm Nd:YLF laser emission under direct 880 nm pumping

The quasi-three-level 908-nm continuous-wave laser emission under direct diode laser pumping at 880 nm into emitting level ⁴ F _3/2 of Nd:YLF have been demonstrated. An end-pumped Nd:YLF crystal yielded 4.7 W of output power for 11.8 W of absorbed pump power. The slope efficiency with respect to the absorbed pump power was 43.3%. Comparative results obtained for the pump with diode laser at 808 nm, into the highly-absorbing ⁴ F _5/2 level, are given in order to prove the advantages of the 880-nm wavelength pumping.     

Intracavity Raman laser generating a third stokes component at 1.5 μm

The lasing properties of an intracavity Nd:KGW Raman laser which converts the multimode radiation of an Nd:KGW laser operating on the ⁴ F _3/2–⁴ I _11/2 transition into the third Stokes component at a wavelength of 1.5 μm are studied. The energy in the third Stokes component is found to increase essentially linearly with the electrical energy delivered to the flashlamp. Lasing at the third Stokes component begins in the central portion of the Nd:KGW crystal and then propagates to its boundaries. Reducing the geometric aperture of the multimode pump beam in the Raman crystal lowers the divergence of the Stokes emission. For a source pump energy of 6 J, the intracavity Raman laser emits 14.7 mJ pulses of duration 3–4 nsec which are safe to the eyes. The divergence of the Raman laser beam at a level of 86% of the total energy is ≈ 9 mrad.     

Continuous-wave high-power Nd:YAG-KNbO3 laser at 473 nm

A continuous-wave high-power Nd:YAG laser operating on the ⁴F_3/2→⁴I_9/2 transition at 946 nm and intracavity frequency-doubled to 473 nm by a KNbO₃ nonlinear crystal at room temperature is reported. The Nd:YAG laser outputs a randomly polarized beam of 3.8 W maximum power (38% optical-to-optical efficiency and 44% slope efficiency with respect to the absorbed pump power) at the 946 nm fundamental wavelength. Intracavity frequency-doubling with a 2.0-mm thick KNbO₃ crystal in a linear resonator yielded 159-mW single-ended blue-output with 4.8% optical-to-optical conversion efficiency versus the absorbed pump power. The 473-nm maximum power of 418 mW with 11.6% optical-to-optical conversion efficiency in absorbed power was obtained from a V-type resonator; the overall optical-to-optical conversion efficiency was 6.7%, while the conversion of the available infrared power reached 50%.     

Efficient and compact intracavity-frequency-doubled Nd:GdVO4/KTP laser end-pumped by a fiber-coupled laser diode

A compact and efficient diode-pumped intracavity-frequency-doubled Nd:GdVO₄/KTP green laser is demonstrated with a flat–flat cavity design. With a 1.3 at. % Nd³⁺-doped GdVO₄ crystal and pumped at the weak-absorption peak of 806 nm, the second-harmonic output power at 532 nm was measured to be 1.95 W at an incident pump power of 8.4 W, corresponding to an optical conversion efficiency of 23.2%. The output characteristic at the fundamental wavelength of 1.063 μm was investigated with two different pump wavelengths. More than 4.5-W output power was generated when the laser was pumped at 806.2 nm. Received: 26 July 2000 / Revised version: 18 September 2000 / Published online: 7 February 2001     

Compact diode-side-pumped Nd:YVO<Subscript>4</Subscript> laser in grazing-incidence configuration

The analysis of compact CW diode-side-pumped grazing-incidence-geometry Nd:YVO₄ laser designs is presented. An output power of 5 W (λ=1064 nm) was produced at 17 W of diode pump (conversion efficiency of 30%) in single transverse TEM₀₀ mode operation at high laser beam quality (M_x ²≈1.05 and M_y ²≈1.01). The resonator geometry was analyzed by applying generalized 4×4 matrix modeling of the spatial mode size, including the impact on the laser operation of cavity astigmatism and a thermal lens in the laser slab. The simplicity and compactness of the laser cavities allow their use for technological applications. Received: 31 July 2002 / Published online: 22 January 2003 RID="*" ID="*"Corresponding author. Fax: +44-20/7594-7744, E-mail: m.damzen@ic.ac.uk     

High-efficiency flashlamp-pumped Nd:KGW laser

The laser performance of a Nd:KGW rod has been studied in a single flashlamp cavity in the free running as well as in the Q-switched mode of operation at input energies ranging from 1–25J. The results of Nd:KGW have been compared with Nd:YAG operated under identical experimental conditions. The laser extraction efficiency of the Nd:KGW rod was observed to be 2.5 times higher at a much lower threshold than that of the Nd:YAG rod. The intrinsic slope efficiency was determined to be 2.25% and 8.840% for Nd:YAG and Nd:KGW rods, respectively.     

LD end-pumped c-Cut Nd:YVO<Subscript>4</Subscript>/KTP self-Raman laser at 560 nm

Intra-cavity sum frequency generation (SFG) of c-cut Nd:YVO₄ self-Raman laser was investigated for the first time. A 4 × 4 × 10 mm³ KTP crystal with a type-II phase-matching cutting angle (θ = 83.4°, φ = 0°) was used for SFG between the fundamental light at 1066 nm and first-Stokes light at 1178 nm. The laser system with different curvature radii of output couplers and different pulse repetition frequencies were investigated. At a pump power of 14 W and pulse repetition frequency of 20 kHz, the average output power of yellow-green laser at 560 nm up to 840 mW was achieved, corresponding to a slope efficiency of 7.6% and a conversion efficiency of 6% with respect to diode pump power.     

885 nm pumped,high efficiency single-frequency Nd:YAG ring laser

We report an efficient single-frequency ring laser pumped directly into emitting level by a fiber-coupled laser diode (FCLD) at 885 nm for the first time. 4.8 W laser at 1064 nm was obtained in a 0.7 at % Nd:YAG with 63% slope efficiency and 51.7% light-light efficiency in absorbed pump power. At the same time, the line width of the longitudinal mode was about 50 MHz, and the beam was nearly diffraction-limited with M2 ≈ 1.07.     

Efficient diode-pumped Nd:GGG laser operation at 933.6 and 937.3 nm

CW laser emission on the quasi 3-level (⁴F_3/2→⁴I_9/2) transition in Nd:GGG is reported for different pump focusing and resonator dimensions. A nearly hemispherical plano-concave resonator led at 937.3 nm to a maximum output power of 4.1 W for an incident pump power of 21.7 W, thus corresponding to a slope efficiency of about 23.5%. Laser operation was also obtained for the first time around 933.6 nm by using a glass etalon for frequency selection with a maximum output power of 2.3 W and a slope efficiency of 16% with respect to the incident pump power. Dual-wavelength operation (around 933.6 and 937.3 nm), which offers a potential source to generate THz radiation, is also reported.     

High power diode single-end-pumped Nd:YVO4 laser

A fiber-coupled diode-single-end-pumped Nd:YVO₄ laser with an Nd:YVO₄ crystal of 0.3 at% doping concentration and 3×3×10 mm³ dimensions was reported. 14.850 W of continuous-wave output power in an M² factor of 1.12 was obtained under pump power of 27.365 W, with an optical conversion efficiency of 60.49%, and a slope efficiency of 64.5%.     

Comparative laser study of Nd:KGW and Nd:YAG near 1.3 μm

A comparative study of Nd:KGW and Nd:YAG laser crystals pumped by flashlamp has been conducted near 1.3 μm with output energy up to 1 J and at a repetition rate up to 50 Hz. An average power of 23 W for KGW in free-running mode was achieved with a total efficiency better than 2.8 % for the Nd:KGW and 1.8 % for the Nd:YAG. Received: 9 December 1996 / Revised version: 10 February 1997     

High-power diode-pumped Tm:YLF slab laser

A 2% Tm³⁺-doped LiYF₄(Tm:YLF) slab is double-end-pumped by two laser diode stacks. The pumped volume has a rectangular cross section. The Tm:YLF laser produced 148 W of continuos-wave output at 1912 nm in a beam with M _x ²≈199 and M _y ²≈1.7 for 554 W of incident pump power. The slope efficiency with respect to the incident pump power was 32.6%, and the optical-to-optical efficiency was 26.7%.     

Diode-pumped continuous-wave Nd:YVO<Subscript>4</Subscript> laser with self-frequency Raman conversion

Continuous-wave operation of a diode-pumped Nd:YVO₄ laser with self-frequency Raman conversion is demonstrated. The threshold of Raman generation was measured to be 1.3 W of laser diode power. The maximum output power of Stokes radiation at the wavelength of 1177 nm was up to 50 mW at a laser diode pump power of 2.3 W, corresponding to the slope efficiency of 5%. The beam quality M² of the Stokes radiation was about 1.4. The fluctuations of the Stokes power were minimised down to 4%. PACS 42.55.Ye; 42.60.Pk; 42.65.Dr     

Theoretical and experimental investigations of a diode-pumped high-power continuous-wave 912 nm Nd:GdVO4 laser operation at room temperature

Based on the rate equation of Nd³⁺-doped quasi-three-level lasers, a theoretical model of diode-end-pumped continuous-wave 912 nm Nd:GdVO₄ laser is presented. Lasing threshold and slope efficiency considering reabsorption effect are calculated and analyzed. It is found that the output performance of 912 nm laser operating at room temperature is influenced remarkably by the reabsorption loss and spatial distribution of the pump beam and laser beam. In experiments, the output power and average slope efficiency of 912 nm laser were investigated under different conditions. After optimization at the parameters of laser medium, working temperature and spatial distribution of the pump beam, up to 16.2 W continuous-wave 912 nm laser output was obtained at incident pump power of 67.0 W, with an average slope efficiency of 41.7%, to the best of our knowledge, this is the highest output power of diode-pumped 912 nm Nd:GdVO₄ laser by far.