Exploring light-emitting diode pumped luminescent concentrators in solid-state laser applications.

In the past, there were limited efforts to use light-emitting diodes (LEDs) for pumping solid-state lasers. However, these attempts were overshadowed by the introduction of laser diodes, which offered more favourable pumping conditions. Nevertheless, recent advancements in high-power LEDs, coupled with the utilization of luminescent concentrators (LC), have paved the way for a novel approach to pump solid-state lasers. The combination of LEDs and LC in this LED-LC system presents several advantages, including enhanced ruggedness, stability, and cost-effectiveness compared to other laser pumping methods. This review explores the various techniques employed to pump solid-state lasers using LED-LC as a pump source, along with improvements made to enhance the brightness of LEDs in this context.

Absolute calibration of a streaked optical pyrometer at nanosecond time scale with a luminescent concentrator.

The Streaked Optical Pyrometer (SOP) is a visible diagnostic widely used to study the warm dense matter regime at high energy laser facilities, gas guns, or ion accelerators. It is usually coupled with a Velocity Interferometer System for Any Reflector (VISAR) diagnostic for simultaneous shock wave velocity, reflectivity, and temperature measurements to study the Equation of State (EOS) of materials. While VISAR is a well-mastered technology that provides velocity measurements with low relative uncertainties (close to percent), SOP diagnostics still suffer from high imprecision. In this article, we present a new calibration method in order to obtain absolute temperature measurements with reduced uncertainties. This approach is based on a novel light source: a Ce:YAG luminescent concentrator pumped by LEDs. This device produces enough optical power for calibration at the nanosecond sweep duration of the streak camera. As a demonstration, it has first been installed at the LULI facility and tested on quartz samples shocked at temperatures above 4000 K.

Enhancing brightness of Lambertian light sources with luminescent concentrators: the light extraction issue.

Luminescent concentrators (LC) enable breaking the limit of geometrical concentration imposed by the brightness theorem. They enable increasing the brightness of Lambertian light sources such as (organic) light-emitting diodes. However, for illumination applications, light emitted in the high-index material needs to be outcoupled to free space, raising important light extraction issues. Supported by an intuitive graphical representation, we propose a simple design for light extraction: a wedged output side facet, breaking the symmetry of the traditional rectangular slab design. Angular emission patterns as well as ray-tracing simulations are reported on Ce:YAG single crystal concentrators cut with different wedge angles, and are compared with devices having flat or roughened exit facets. The wedge output provides a simple and versatile way to simultaneously enhance the extracted power (up to a factor of 2) and the light directivity (radiant intensity increased by up to 2.2.).

High-power diode-pumped cryogenically cooled Yb:CaF2 laser with extremely low quantum defect.

High-power diode-pumped laser operation at 992-993 nm under a pumping wavelength of 981 of 986 nm is demonstrated with Yb:CaF2 operating at cryogenic temperature (77 K), leading to extremely low quantum defects of 1.2% and 0.7%, respectively. An average output power of 33 W has been produced with an optical efficiency of 35%. This represents, to the best of our knowledge, the best laser performance ever obtained at such low quantum defects on intense laser lines.

Thermal behaviour of ytterbium-doped fluorite crystals under high power pumping.

We report an in situ thermal study of Yb-doped fluorite crystals Yb:CaF(2) and Yb:SrF(2) under high power pumping, with or without laser operation. The experiment combines simultaneously thermography and measurement of the thermal aberrations. This setup allows us to measure temperature gradients, thermal lens, and absorption coefficients. From these measurements, we evaluate the thermal conductivity, fractional thermal load, and thermo-optic coefficient. Great differences are observed between the lasing and non lasing regimes. Our measured thermal lenses are greater than what are expected from the thermo-optic parameters found in previous work. Based on this thermal study, we design a laser cavity operating with large output power and TEM(00), leading to better performances for Yb:CaF(2) than Yb:SrF(2).

Nd:GdVO4 as a three-level laser at 879 nm.

We present what we believe to be the first true three-level laser based on a Nd-doped crystal. From the 4F3/24I9/2 laser transition, the lower laser level being the ground state, emission at 879 nm in NdGdVO4 has been obtained with diode pumping. Up to 0.8 W of power has been achieved in cw operation and 24 microJ per pulse (35 ns) in the Q-switched regime. Intracavity second-harmonic generation in the pulsed regime is also demonstrated with 17 8 mW of average output power at 439.5 nm, corresponding to an energy of 17microJ per pulse.

47-fs diode-pumped Yb3+:CaGdAlO4 laser.

The experimental demonstration of a diode-pumped passively mode-locked femtosecond laser based on an Yb3+:CaGdAlO4 single crystal is reported. The oscillator is directly diode pumped by a high-brightness 5 W fiber coupled laser diode, and pulses are produced by use of a semiconductor saturable-absorber mirror. It permits the production of pulses as short as 47 fs at 1050 nm, which are to our knowledge the shortest laser pulses obtained from an oscillator based on Yb3+-doped bulk materials. The average power is 38 mW, and the repetition rate is 109 MHz.

Diode-pumped passively mode-locked Nd:YVO4 laser at 914 nm.

We demonstrate, for the first time, to our knowledge, a diode-pumped passively mode-locked Nd:YVO4 laser, operating on the 4F(3/2)-4I(9/2) transition of the neodymium ion at 914 nm. We obtained 8.8 ps pulses at approximately 914 nm at a repetition rate of 94 MHz, and an averaged output power of 87 mW by using a semiconductor saturable absorber mirror.

Diode-pumped continuous-wave and femtosecond laser operations of a heterocomposite crystal Yb3+: SrY4(SiO4)3O parallel Y2Al5O12.

We report cw and femtosecond laser operations under diode pumping of a diffusion-bonding heterocomposite Yb-doped crystal: Yb3+:SrY4(SiO4)3O parallel Y2Al5O12(YAG paralell SYS:Yb). To show the advantages of this heterocomposite crystal over classical Yb:SYS crystal, we first investigate the high-power cw regime. A cw power of 4.3 W is demonstrated. The femtosecond regime is also investigated, and 1-W-average-power, 130-fs pulses at 1070 nm are produced, which represents, to our knowledge, the first demonstration of an Yb-doped heterocomposite mode-locked laser.

Fluorescence lifetime imaging with a low-repetition-rate passively mode-locked diode-pumped Nd:YVO4 oscillator.

We report a wide-field fluorescence lifetime imaging microscope based on a low-repetition-rate (3.7-MHz) passively mode-locked diode-pumped laser source. This inexpensive and compact laser source operating in the visible and UV range can excite a wide range of fluorophores of biological interest. We demonstrate that the power of this laser source is highly sufficient for studying biological systems with low quantum yields (autofluorescence of tissues and stained living cells). The maximum measurable lifetime is also strongly increased with this laser source, as fluorescence intensity measurement can occur 250 ns after the excitation pulse.

High-power diode-pumped Yb3+:CaF2 femtosecond laser.

We report what is believed to be the first demonstration of a high-power passively mode-locked diode-pumped femtosecond laser based on an Yb3+:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at. % Yb3+ -doped sample and prisms for dispersion compensation we obtained pulses as short as 150 fs, with 880 mW of average power and up to 1.4-W average output power, with a pulse duration of 220 fs, centered at 1049 nm. The laser wavelength could be tuned from 1040 to 1053 nm in the femtosecond regime. Using chirped mirrors for dispersion compensation, the oscillator provided up to 1.74 W of average power, with a pulse duration of 230 fs, corresponding to a pulse energy of 20 nJ and a peak power of 85 kW.

High-power tunable diode-pumped Yb3+:CaF2 laser.

Results of diode-pumped cw laser operation of an Yb3+:CaF2 single crystal are reported for what is to our knowledge the first time. With a 5-at.% Yb3+ -doped sample we obtained 5.8-W output power at 1053 nm for 15 W of incident power at 980 nm. The laser wavelength could be tuned from 1018 to 1072 nm, and a small-signal gain as high as 1.8 was achieved, showing the great potential of Yb3+:CaF2 as an amplifier medium for femtosecond pulses.

Passively mode-locked diode-pumped Nd:YVO4 oscillator operating at an ultralow repetition rate.

We demonstrate the operation of an ultralow-repetition-rate, high-peak-power, picosecond diode-pumped Nd:YVO4 passively mode-locked laser oscillator. Repetition rates lower than 1 MHz were achieved with the use of a new design for a multiple-pass cavity and a semiconductor saturable absorber. Long-term stable operation at 1.2 MHz with a pulse duration of 16.3 ps and an average output power of 470 mW, corresponding to 24-kW peak-power pulses, is reported. These are to our knowledge the lowest-repetition-rate high-peak-power pulses ever generated directly from apicosecond laser resonator without cavity dumping.

Diode-pumped Yb:Sr(3)Y(BO(3))(3) femtosecond laser.

We have developed a diode-pumped Yb(3+)Sr(3)Y(BO(3))(3) (Yb:BOYS) laser generating 69-fs pulses, at a central wavelength of 1062 nm. This laser is mode locked by use of a semiconductor saturable-absorber mirror and emits 80 mW of average power at 113 MHz. This is, to our knowledge, the first mode-locked Yb:BOYS laser and the shortest duration obtained from an ytterbium laser with a crystalline host. The central wavelength can be tuned from 1051 to 1070 nm, for sub-100-fs pulses. We have also achieved an average power as high as 300 mW with pulse duration of 86 fs at 1068 nm.

Apatite-structure crystal, Yb(3+):SrY(4)(SiO(4))(3)O, for the development of diode-pumped femtosecond lasers.

We report what is believed to be the first diode-pumped Yb(3+): SrY(4)(SiO(4)) (3)O laser. We investigate both the cw and the mode-locked regimes. In the cw regime an average output power of 1.05 W is demonstrated for 3.6 W of incident pump power. In the femtosecond regime a pulse duration of 94 fs for an average power of 110 mW is obtained at a central wavelength of 1068 nm. This is, to our knowledge, the first femtosecond mode-locked oscillator made with an Yb-doped apatitelike crystal. These properties are related to the unique spectroscopic properties of Yb(3+) ions in this atypical apatite-family crystal.

High-Power Continuous-Wave Diode-Pumped Nd:YAlO(3) Laser that Emits on Low-Gain 1378- and 1385-nm Transitions.

Efficient operation of a diode-pumped Nd:YAlO(3) laser on low-gain 1378- and 1385-nm transitions is reported for the first time, to our knowledge. A three-mirror folded cavity with a prism yielded a cw laser output power of 800 mW for an absorbed pump power of 11 W. The laser beam was TEM(00). We managed to eliminate the instabilities in the output power by purging the cavity of water vapor with nitrogen.

Generation of 90-fs pulses from a mode-locked diode-pumped Yb(3+):Ca(4)GdO(BO(3))(3) laser.

A diode-pumped Yb>(3+):Ca(4)GdO(BO>(3))(3) (Yb:GdCOB) laser generating 90-fs pulses at a center wavelength of 1045 nm is demonstrated. This is, to our knowledge, the shortest pulse duration obtained from an ytterbium laser with a crystalline host. This laser is mode locked with a high-finesse semiconductor saturable-absorber mirror and emits 40 mW of average power at a repetition rate of 100 MHz.

High-repetition-rate 300-ps pulsed ultraviolet source with a passively Q-switched microchip laser and a multipass amplifier.

We demonstrate a new kind of picosecond laser source in the UV at a high repetition rate of -45 kHz , using only passive, compact, and simple elements. This system is based on a microchip laser and a very efficient multipass amplifier, both pumped with recently developed high-brightness laser diodes. The system has been optimized to deliver, at a high repetition rate, subnanosecond pulses at the wavelength 355 nm with an energy per pulse of close to 1 muJ (38-mW average power). This source is to our knowledge the first totally passive 300-ps UV laser source at this high repetition rate.

Efficient and tunable continuous-wave diode-pumped Yb3+:Ca4GdO(BO3)3 laser.

A Yb(3+):Ca(4)GdO(BO(3))(3) (Yb:GdCOB) crystal has been diode pumped for the first time to our knowledge. We obtained 47.5% slope efficiency at 6 degrees C, producing 191 mW of power at 1050 nm, with a 2.4% output coupler. Temperature does not significantly affect the laser performance: At room temperature we still obtained 180 mW of power for the same cavity. We achieved tunability of the Yb:GdCOB laser from 1035 to 1088 nm with a 1.7% output coupler and 100-nm tunability with a low-transmission output coupling (T = 0.03%).

Intracavity testing of KTiOPO4 crystals for second-harmonic generation at 532 nm.

We have developed a diode-pumped Nd:YVO4 cw laser for testing KTiOPO4 crystals designed for intracavity second-harmonic generation at 532 nm. We demonstrate that this source is extremely sensitive to defects inside the crystal, inducing losses at 1064 nm and an index mismatch between fundamental and harmonic waves.