Intracavity Birefringent Filter Research Articles

Quasi-three-level continuous wave Nd:Na2La4(WO4)7 lasers at 0.9 μm

A diode-pumped continuous wave (CW) Nd:Na2La4(WO4)7 (Nd:NLW) laser operating at 0.9 μm on 4F3/2 → 4I9/2 transition was demonstrated. Four single- wavelengths (the 889 nm and 912 nm in σ-polarization, the 890 nm and 905 nm in π-polarization) were obtained by rotating an intracavity birefringent filter (BF).At an absorbed pump power of 17.4 W at 808 nm, the highest output power of single-wavelength at 912 nm was 3.4 W. Furthermore, the dual-wavelength at 889 and 912 nm in σ-polarization and the dual-wavelength at 890 and 905 nm in π-polarization were also achieved, respectively. At an absorbed pump power of 17.4 W, the maximum total output powers of the dual-wavelengths at 889 and 912 nm was 2.12 W. To the best of our knowledge, this is the first quasi-three-level Nd:NLW laser operating at 0.9 μm.

Pushing the tuning limits of femtosecond Yb-based solid-state lasers to 1 µm: a Yb:YVO4 laser tunable down to 1004 nm.

We have obtained what we believe to be the shortest fs tuning wavelength (1004 nm) from a Yb-based solid-state laser system. As the working horse, we have chosen Yb:YVO4 due to its blueshifted gain spectrum. While using a single 10 W 952 nm diode for pumping and a semiconductor saturable absorber mirror (SESAM) for mode-locking, we have achieved 266 fs long pulses with up to 1.24 W of output power around 1021 nm. Using an intracavity birefringent filter, the central wavelength of the fs pulses could be tuned smoothly between 1004-1038 nm and 1009-1061 nm while employing the E//a and E//c axis of the material, respectively. By using an additional hard aperture to increase the modulation depth, we have also attained 100 fs level pulses in the 1012.5-1019 nm range, which shows the suitability of the system in seeding cryogenic Yb:YLF-based amplifiers.

Semiconductor saturable absorber mirror mode-locked Yb:YLF laser with pulses of 40 fs.

We have generated pulses as short as 40 fs with an average power of 265 mW from a semiconductor saturable absorber mirror (SESAM) mode-locked Yb:YLF oscillator employing a 1% transmitting output coupler (OC). The room-temperature laser is pumped by a low-cost 960 nm single-emitter multimode diode and dispersion compensation is provided via double chirped mirrors (DCMs). The 40-fs pulses are centered around 1050 nm with a width of 34 nm at a repetition rate of 87.3 MHz. By increasing the output coupling to 5% and by using Gires-Tournois interferometer (GTI) mirrors for dispersion compensation, we have also demonstrated 380-fs pulses with 1.85 W of average power around 1025 nm at a repetition rate of 190.4 MHz. Using an intracavity off-surface optic axis birefringent filter, the central wavelength of the pulses could be tuned in the 1020-1025 nm and 1019-1047 nm ranges for the 5% and 1% transmitting OCs, respectively. To the best of our knowledge, these are the shortest pulses and highest average and peak powers generated from room-temperature Yb:YLF lasers to date.

Mode-locked Cr:LiSAF laser far off the gain peak: tunable sub-200-fs pulses near 1 µm.

We report, to the best of our knowledge, the first mode-locking results of a Cr:LiSAF laser near the 1 µm region. The system is pumped only by a single 1.1 W high-brightness tapered diode laser at 675 nm. A semiconductor saturable absorber mirror (SESAM) with a modulation depth of 1.5% and non-saturable losses below 0.5% was used for mode-locking. Once mode-locked, the Cr:LiSAF laser produced almost-transform-limited sub-200-fs pulses with up to 12.5 mW of average power at a repetition rate of 150 MHz. Using an intracavity birefringent filter, the central wavelength of the pulses could be smoothly tuned in the 1000-1020 nm range. Via careful dispersion optimization, pulse widths could be reduced down to the 110-fs level. The performance in this initial study was limited by the design parameters of the SESAM used, especially its passive losses and could be improved with an optimized SESAM design.

Zinc-indiffused MgO:PPLN waveguides for blue/UV generation via VECSEL pumping.

We present the design and characterization of a zinc-indiffused periodically poled lithium-niobate ridge waveguide for second-harmonic generation of ∼390nm light from 780nm. We use a newly developed, broadband near-infrared vertical external-cavity surface-emitting laser (VECSEL) to investigate the potential for lower-footprint nonlinear optical pump sources as an alternative to larger commercial laser systems. We demonstrate a VECSEL with an output power of 500mW, containing an intracavity birefringent filter for spectral narrowing and wavelength selection. In this first demonstration of using a VECSEL to pump a nonlinear waveguide, we present the ability to generate 1mW of ∼390nm light with further potential for increased efficiency and size reduction.

Stable fundamental and dual-pulse mode locking of red-emitting VECSELs

We present a thorough characterization of a red-emitting mode-locked semiconductor disk laser producing the first stable fundamental mode-locked pulse train in the red spectral range. The achievable temporal FWHM pulse length of the Lorentzian-shaped pulses is just below 3 which represents the shortest pulses obtained in a fully-resonant absorber and gain structure design. We also include an intracavity birefringent filter to stabilize and tune the emission wavelength between and . This, in combination with a real-time sampling of the emitted pulse train, allows us to distinguish three regimes according to their round-trip dynamics. The first regime resembles stable fundamental mode locking and is observed for wavelengths below while for an emission wavelength of the continuous wave regime is observed. These two operating regimes enclose the dual-pulse mode locking regime appearing between and . This regime is characterized by an energy exchange between the individual pulses of the dual-pulse mode locking regime and we clearly relate the side-peaks in the radio frequency spectrum to the dual-pulse energy-exchange frequency and the temporal interpulse spacing to the individual arm lengths of the gain-folded external cavity. Overall, we attribute these different operating regimes to near-bandgap operation of the SESAM which allows for dispersion of saturation fluence and modulation depth.

High-power passively mode-locked cryogenic Yb:YLF laser.

We report, to the best of our knowledge, the first mode-locked operation of Yb:YLF gain media at cryogenic temperatures. A saturable Bragg reflector was used for initiating and sustaining mode locking. Once aligned, the system was self-starting and quite robust. Using output couplers in the 10-40% range, 3-5 ps long pulses with an average power as high as 28 W were achieved. The repetition rate was 46.45 MHz, and the corresponding pulse energy and peak power were as high as 602 nJ and 126.5 kW, respectively. The central wavelength of the mode-locked pulses could be tuned in the 1013.5-1019 nm range using an intracavity birefringent filter. The achieved output power performance is two to three orders of magnitude higher than previous room-temperature Yb:YLF systems.

Suppression of FM-to-AM conversion in a broadband Nd:glass regenerative amplifier with an intracavity birefringent filter.

In order to suppress the frequency modulation to amplitude modulation (FM-to-AM) conversion induced by a Nd:glass regenerative laser amplifier, a birefringent quartz crystal was designed by theoretical simulation and inserted into the regenerative amplifier. A broadband Nd:glass regenerative laser amplifier with a flattop region of ∼3.7 nm in the gain spectrum was developed. An all-fiber front-end system was used to generate a 2 ns shaped pulse with a spectral width of ∼0.5 nm, which was broadened by a two-stage phase modulator. Then, the laser pulse was amplified by a spectral-broadened regenerative amplifier. The amplified output temporal waveform modulation depth was reduced from a maximum of 47.7% to 17.3% at a center wavelength of 1053.328 nm. The experimental results show that the FM-to-AM conversion can be effectively suppressed in the spectral-broadened Nd:glass regenerative laser amplifier, which indicates that it has potential application as a preamplifier of large-scale laser facilities.

Dual-Wavelength Nanosecond Nd:YVO4 Laser With Switchable Inhomogeneous Polarization Output

We report a compact dual-wavelength nanosecond Nd:YVO4 laser with switchable radially and azimuthally polarized output. The single-wavelength (1064.66 nm) or dual-wavelength (1064.50 and 1064. 66 nm) operation can be delivered and switched by adjusting the intracavity birefringent filter. In addition, the switchable radially and azimuthally polarized beams could be obtained in the continuous-wave (CW) and actively Q-switched operation via the intracavity polarization manipulation. In the CW operation regime, the slope efficiency of single- and dual-wavelength laser could reach up to 11.3% and 25.5%, respectively. For the actively Q-switched operation, the single-wavelength laser can deliver pulse with the shortest duration 30 ns and the peak power 0.65 kW, and the dual-wavelength laser can deliver the pulse with the shortest pulse duration 28 ns and the peak power 0.83 kW. This multifunctional laser could enrich the manipulation potential of the solid-state laser, and would benefit lots of applications, such as THz wave generation, materials processing, fiber, and free space communication.

1.4 µm continuous-wave diamond Raman laser.

The longest wavelength (~1.4 µm) emitted by a diamond Raman laser pumped by a semiconductor disk laser (SDL) is reported. The output power of the intracavity-pumped Raman laser reached a maximum of 2.3 W with an optical conversion efficiency of 3.4% with respect to the absorbed diode pump power. Narrow Stokes emission (FWHM <0.1 nm) was attained using etalons to limit the fundamental spectrum to a single etalon peak. Tuning of the Raman laser over >40 nm was achieved via rotation of an intracavity birefringent filter that tuned the SDL oscillation wavelength.

100-nm tunable femtosecond Cr:LiSAF laser mode locked with a broadband saturable Bragg reflector.

We report broad tunability of a femtosecond (fs) diode-pumped Cr:LiSAF laser mode-locked with a broadband saturable Bragg reflector (SBR). The SBR had seven pairs of AlxOy(n∼1.5) and Al0.17Ga0.83As(n∼3.5) layers in its Bragg stack, enabling a 250nm reflectivity bandwidth around 850nm. A 6-nm-thick strained In0.15Ga0.85As quantum well placed between Al0.17Ga0.83As cladding layers was used as a broadband saturable absorber in the 800-920nm wavelength range. The laser was pumped by 6 single mode diodes-four at 640 nn and two at 660nm. Mode locking was self-starting and fs pulses could be continuously tuned from 800nm to 905nm by an intracavity birefringent filter with an out-of-plane optic axis. The pulse widths varied from 70fs to 255fs as the laser was tuned. The laser had an 85.5MHz repetition rate and the output power varied from 80mW to 180mW with tuning.

Wavelength tuning in cryogenically cooled lasers based on Er-doped orthovanadates.

Continuous tuning between 1590 and 1612nm has been demonstrated in cryogenically cooled lasers with composite active media consisting of Er:YVO4, Er:LuVO4, and Er:GdVO4 crystals resonantly pumped by a fiber-coupled laser diode emitting at 1529nm. Wavelength tuning was implemented using an intracavity single-plate birefringent filter.

Tunable eye-safe Er:YAG laser

Er:YAG crystal was investigated as the gain medium in a diode (1452 nm) pumped tunable laser. The tunability was reached in an eye-safe region by an intracavity birefringent filter. The four tuning bands were obtained peaking at wavelengths 1616, 1632, 1645, and 1656 nm. The broadest continuous tunability was 6 nm wide peaking at 1616 nm. The laser was operating in a pulsed regime (10 ms pulse length, 10 Hz repetition rate). The maximum mean output power was 26.5 mW at 1645 nm. The constructed system demonstrated the tunability of a resonantly diode-pumped Er:YAG laser which could be useful in the development of compact diode-pumped lasers for spectroscopic applications.

1180 nm VECSEL with output power beyond 20 W

The highest power result for an optically-pumped single-chip vertical external-cavity surface-emitting laser with emission near 1180 nm is reported. The gain mirror was grown by molecular beam epitaxy and incorporated a strain compensated GaInAs/GaAs/GaAsP active region. An intra-cavity diamond heat spreader was attached to the gain mirror for thermal management. In free-running operation, the laser emitted more than 20 W at a mount temperature of about 12 °C. The output spectrum was centred between 1165–1190 nm depending on the mount temperature and pump power. By using an intra-cavity birefringent filter, the full width at half-maximum linewidth could be narrowed to ≤1 nm and at the same time achieved approximately 14 W of output power near 1178 nm. Moreover, the lasing wavelength could be tuned over more than 40 nm.

Generation of deep ultraviolet narrow linewidth laser by mixing frequency Ti:sapphire laser at 5 kHz repetition rate

We demonstrate a scheme to generate deep ultraviolet source by the single-stage high-power Ti:sapphire laser with linewidth of 0.05 nm cryogenically operating at repetition rate of 5 kHz. The fundamental laser was tuned by an intracavity birefringent filter and three etalons with an output power greater than 8 W, corresponding to about 17% optical efficiency. The pulse width was 112 ns and M2<1.1. By using the nonlinear crystals BiB3O6 and KBe2BO3F2, the output power of 2.2 W at second harmonic and 8.5 mW at fourth harmonic laser of about 195 nm were produced. This compact high-repetition rate laser with narrow linewidth would be a promising tunable source for spectroscopy.

Sub-MHz-Linewidth 200-mW Actively Stabilized 2.3-μm Semiconductor Disk Laser

We report on the realization of an actively stabilized single-frequency vertical-external-cavity surface-emitting semiconductor laser (VECSEL) at a wavelength of 2.3 μ m. The laser was locked to a high-finesse Fabry-Pérot interferometer with a free-spectral range of 1 GHz. From the error signal of the control feedback loop a laser linewidth of 390 kHz could be derived (1-s sampling time). Reducing the sampling time to 100 μs, a much narrower linewidth of 55 kHz was obtained, indicating the dominant effect of low-frequency technical noise. The output power exceeded 200 mW. By rotating the intracavity birefringent filter, a wide tuning range of 62 nm could be achieved. Changing the resonator length with the help of a piezoelectric transducer mounted to a cavity mirror, a modehop-free fine tuning range of 5.5 GHz was achieved.

Broadly tunable 1250 nm quantum dot-based semiconductor disk laser

Optically pumped semiconductor disk lasers with antiresonant design based on Stranski-Krastanow-grown quantum dots are demonstrated to extend the spectral coverage of such type of devices up to 1250 nm. A continuous wave output power up to 1.6 W was achieved using an intracavity diamond heat spreader. Intracavity birefringent filter was used to tune the wavelength of the device in 25 nm range.

Characterization of Single-Frequency Yb:$ \hbox{KYF}_{4}$ Lasers at 1.03 $\mu\hbox{m}$ for Optical Frequency Metrology

A longitudinally pumped, widely tunable, solid-state Yb:KYF4 laser was developed with special design for applications to optical frequency metrology and absolute frequency stabilization. The KYF4 crystalline host, combined with efficient diode pumping, allows for wide wavelength tunability at about 1.03 mum in a single transverse mode. Two different laser cavity designs were experimentally investigated. The combined use of an intracavity birefringent filter and uncoated glass etalons provides single-frequency output power at the 100-mW level in a folded-cavity resonator. A second hemispherical linear cavity was also developed with one or two coated intracavity etalons for single-frequency operation. The novel laser sources were thoroughly characterized in terms of output power and beam quality, amplitude noise, wavelength tunability, and single-axial-mode operation. High-quality TEM00 single-frequency laser radiation opens the way to the development of a new optical frequency standard based on the I 2 molecule at 0.5- mum wavelength.

GaN diode-pumping of red semiconductor disk laser

A red-wavelength semiconductor disk laser (SDL) optically pumped by gallium nitride laser diodes is reported. This is believed to be the first demonstration of a directly diode-pumped visible wavelength SDL. In this initial demonstration, pump-power-limited continuous-wave output power up to 12.2 mW was achieved around room temperature in a single transverse mode with 2 output coupling. Insertion of an intracavity birefringent filter allowed tuning of the output over 11 nm around a centre wavelength of 672 nm.

Tunable single-frequency diode-pumped, intracavity-doubled, traveling-wave Nd:YAG and Yb:YAG lasers

Single-frequency traveling-wave Nd:YAG and Yb:YAG lasers combining the functions of intracavity second harmonic generation and birefringent filter on one nonlinear crystal are discussed. The lasers were developed for spectroscopy and metrology applications. Output characteristics and spectral tuning ranges of the lasers are presented.