Round-trip Cavity Loss Research Articles

Drastic thermal effects reduction through distributed face cooling in a high power giant-pulse tiny laser

Shape design of sapphire/Nd3+:YAG based distributed face cooling (DFC) chip is reported with reduction of thermal effects as compared with those from a conventional Nd3+:YAG chip. The CW diode laser pumped round-trip cavity loss was 0.51% from a 9-disk bonded DFC chip, which was close to the theoretically calculated total Fresnel reflection loss of 0.2% from 8 Sapphire/Nd3+:YAG interfaces. The depolarization ratio from an 8-disk bonded DFC chip was 40 times lower than that from YAG/Nd3+:YAG chip. The DFC chip underwent no crack at pump power of 86 W while Nd3+:YAG single chip suffered crystal crack under pump power around 54 W. Over megawatt peak power from DFC tiny integrated laser is demonstrated at 1 kHz with 3-pulse burst modes. It is concluded that DFC structure could relieve thermal effects as expected.

CW and tunable performances of Yb3+:LuAG transparent ceramics with different doping concentrations

We report the CW laser operation and wavelength tunability of 10 at%, 15 at% and 20 at% Yb3+-doping LuAG ceramics pumped at 970 nm. The absorption saturation effects were taken into account herein. For 10 at% Yb3+-doping sample, the maximum slop efficiency and output power was 60.7% and 1.8 W, respectively. Furthermore, the slop efficiencies of 52.3% (15 at%) and 46.5% (20 at%) were reported. What's more, the maximum optical-to-optical efficiency for our samples was determined to be 40.1%, 36.8%, and 33.1% at the incident pump power of 4 W, respectively. The round-trip cavity loss of the laser system based on our Yb3+:LuAG ceramics were evaluated. The tuning curve of a 20 at% Yb3+:LuAG ceramic extended from 1018 nm up to 1062 nm, and that of 10 at% and 15 at% samples became much more broader, making Yb3+:LuAG ceramics possible candidates for ultrashort pulse generation.

Deep red diode-pumped Pr³⁺:KY₃F₁₀ continuous-wave laser.

We report the first observation of continuous-wave laser emission at 720 nm, in the deep red region, of a Pr3+:KY3F10 (Pr:KYF) single crystal, pumped with a blue InGaN-based laser diode at 446 nm. We employed a hemispherical cavity with three different output coupling mirrors transmitting 0.7%, 1.4%, and 2.7% of laser radiation. We obtained a maximum output power of 207 mW with a slope efficiency of 24.3%, comparable for the first time to what has been reported for other praseodymium-doped fluoride crystals. The round-trip cavity losses for our sample were estimated to be between 0.3% and 0.6%, a remarkably small value for this material.

Emission properties and CW laser operation of Pr:YLF in the 910 nm spectral range.

The polarized emission spectra for the 3P0→1G4 emission transition of the Pr3+ ion around 910 nm in the Pr3+:LiYF4 (Pr:YLF) laser crystal were registered and calibrated in unit of cross sections for the first time. Continuous-wave (CW) laser operation is demonstrated at 915 nm in π polarization by pumping the crystal with an optically pumped semiconductor laser (OPSL) at 479.2 nm. An output power of 218 mW is thus obtained with a laser slope efficiency of about 24% for an output coupler (OC) transmission of 1.9%. CW laser operation is also demonstrated at 907 nm in σ polarization by using a thin plate oriented at Brewster angle. An output power of about 89 mW with a slope efficiency of about 10% is then obtained for an OC transmission of 0.8%.The round-trip cavity losses are estimated for different experimental cavity configurations to be about 1% and the typical beam quality M2 factors measured in the transverse x and y directions are found equal to about 1.07 and 1.04, respectively. Finally, we also report on a double laser wavelength operation by using an OC with a transmission of about 0.05%, such effect resulting from joint-etalon effects inside the cavity.

Investigation of the roundtrip cavity loss in laser diode pumped erbium:ytterbium-phosphate glass microchip lasers

We present a method for determination of the roundtrip cavity loss in the laser diode pumped erbium:ytterbium-codoped phosphate glass microchip laser. Slope efficiency and laser threshold were measured in the experiment and their dependencies on roundtrip cavity loss were derived through rate equations. According to the energy levels, cumulative upconversion and cooperative upconversion are taken into consideration to ensure the accuracy of the derivation. Roundtrip cavity losses in different cavity configurations were investigated.

Multiwavelength fibre laser with wavelength selectable from 1590 to 1645 nm

A multiwavelength fibre laser with a semiconductor optical amplifier is reported. The lasing wavelength of the laser can be adjusted from 1590 to 1645 nm by adjusting the round-trip cavity loss. Simultaneous lasing of over 40 wavelengths with signal-to-noise ratio of over 40 dB was achieved from 1612 to 1645 nm.

Universality of mode-locked jitter performance

It is shown experimentally that the jitter of actively mode-locked laser pulses is determined by two factors: first, by spontaneous noise associated with cavity loss, and second, by round-trip propagation time. As the round-trip time is increased, a characteristic frequency which defines the high-frequency limit of phase noise decreases. For a comparable round-trip time and cavity loss, the jitter of mode-locked lasers based on diverse gain media, whether semiconductor or erbium ion is universal and independent of the upper-state transition lifetime.

Optical fiber ring resonator characterization by optical time-domain reflectometry

A novel method for characterization of optical fiber resonators by an optical time-domain reflectometry (OTDR) technique is reported. This easy-to-use technique yields accurate results for cavity lengths ranging from a few meters to several kilometers. A simple relationship is established between the round-trip cavity loss and the position where the OTDR signal is maximum. The value obtained for the round-trip cavity loss turns out to be quite insensitive to uncertainties in the determination of the OTDR maximum position.

Lasing in visible of a storage-ring free electron laser at ETL

Lasing at 598 nm of a storage-ring free electron laser (FEL) has been observed at the Electrotechnical Laboratory (ETL), though the output power was weak because of the low gain due to the short straight section of the ring. The storage ring was operated in a 3-bunch mode at 230 MeV instead of a full 18-bunch mode. Coherent instabilities of the stored electron beam was suppressed by exploiting a Landau cavity with the 2nd harmonic of the ring frequency 171.62 MHz. The beam current during the oscillation ranged from 5 mA to 3 mA per bunch. A 1.47 m optical klystron consisting of NEOMAX-35 permanent-magnet blocks has been used to enhance the FEL gain. The number of periods (76 mm) in a usual-undulator section is eight. The round-trip cavity loss of dielectric multilayer mirrors, separated by 5.238 m, was measured to be about 2×10 −4. The laser linewidth was about 0.3 nm, and the peak FEL output power was deduced to be at least 10 mW from a rough measurement.

Free electron laser experiment at ETL

A FEL experiment using a storage ring and an optical klystron is being carried out at the Electrotechnical Laboratory (ETL) for the purpose of achieving laer oscillation at around 590 nm. The storage ring is a medium-sized one with a maximum energy of 800 MeV, and the optical klystron is made of NEOMAX-35 permanent magnets and is 1.47 m in length. Gain was measured at around 590 nm to be 1 × 10 −4 with a low beam current of 1.6 mA/bunch, which is just above the initial round-trip cavity loss measured by a cavity-decay-time method. A laser-oscillation experiment is in progress in the higher beam-current region.

Room-temperature continuous-wave operation of a Ti:Al_2O_3 laser

Room-temperature cw operation of a Ti:Al(2)O(3) laser has been demonstrated for the first reported time. Laser emission at 770 nm was excited with an all-line Ar-ion laser pump. The maximum output power was 1.6 W. Values of (64 +/- 10)% for the internal quantum efficiency and (2.4 +/- 0.5)% for the round-trip cavity loss are obtained from the thresholds and slope efficiencies measured with 0.7 and 4.9% output couplers. The cavity-loss value places an upper bound of 0.007 cm(-1) on the absorption coefficient of the laser rod for the pi polarization (E ||ĉ) || at 770 nm, compared with 0.73 cm(-1) measured at 490 nm, the peak of the Ti(3+) pump band.

LED end-pumped Nd:YAG lasers

Experimental results are reported on the room-temperature operation of Nd:YAG lasers end pumped with an LED. The radiation from a 10-percent-efficient 0.46-mm-diam domed LED was coupled to the end of a 0.46-mm-diam × 5.0-mm-long laser rod with a large hemispherical reflector. At 20°C, a multimode laser power of 0.25 mW was obtained at an LED current of 250 mA. By measuring the variation of threshold pump power with rod temperature and the laser power versus pump power just above threshold, both the laser cavity loss and the output mirror transmission were determined. A round-trip cavity loss as low as 0.022 percent was measured. A calculation of the fractional pump power absorbed in the rod for the LED spectrum gave 56 percent for a 5-mm-long rod while measurements showed that 30 to 35 percent of the LED power was being absorbed indicating an LED-to-laser rod coupling efficiency of 54 to 63 percent for this arrangement. With such efficient absorption of pump power and low cavity loss, end-pumped Nd:YAG lasers with high slope efficiencies above threshold are possible.