Jonna Paajaste

Passively Q-switched Tm 3+ , Ho 3+ -doped silica fiber laser using a highly nonlinear saturable absorber and dynamic gain pulse compression

We demonstrate a compact core-pumped 2 microm Tm(3+), Ho(3+)- doped all-fiber laser passively Q-switched with an antimony-based saturable absorber. The 20 ns pulses are the shortest Q-switched pulses from a fiber laser operating beyond 1850 nm and were produced at a repetition rate of 57 kHz and pulse energy of 15 microJ using a short-length (4 ns) cavity. The large absorber modulation depth of approximately 70% together with transient gain compression is shown to provide an efficient mechanism for Q-switched pulse shortening.

Mode-locking of 2 μm Tm,Ho:YAG laser with GaInAs and GaSb-based SESAMs

We have investigated passive mode-locking of Tm,Ho:YAG lasers with GaInAs- and GaSb-based semiconductor saturable absorber mirrors (SESAMs). With a GaInAs-based SESAM, stable dual-wavelength mode-locking operation was achieved at 2091 nm and 2097 nm, generating pulses with duration of 56.9 ps and a maximum output power of 285 mW. By using the GaSb-based SESAMs, we could generate mode-locked pulses as short as 21.3 ps at 2091 nm with a maximum output power of 63 mW. We attribute the shorter pulse duration obtained with the GaSb SESAMs to the ultrafast recovery time of the absorption and higher nonlinearity compared to standard GaInAs SESAMs.

Picosecond passively mode-locked GaSb-based semiconductor disk laser operating at 2μm

We report on a passively mode-locked optically pumped GaSb-based semiconductor disk laser producing stable picosecond optical pulses at a 1.95 μm wavelength. The gain mirror was comprised of a 15 quantum well InGaSb/GaSb structure. A fast semiconductor saturable absorber mirror with three InGaSb/GaSb quantum wells was used to attain self-starting mode-locked operation at a fundamental repetition rate of 881.2 MHz. The laser produced pulses with 30 pJ energy and a duration of 1.1 ps within a factor of 2 of the Fourier limit.

GaSb-based SESAM mode-locked Tm:YAG ceramic laser at 2 µm

Tunable and mode-locked laser operation near 2 µm based on different Tm-doped YAG ceramics, 4 at.% and 10 at.%, is demonstrated. Several designs of GaSb-based surface-quantum-well SESAMs are characterized and studied as saturable absorbers for mode-locking. Best mode-locking performance was achieved using an antireflection-coated near-surface quantum-well SESAM, resulting in a pulse duration of ~3 ps and ~150 mW average output power at 89 MHz. All mode-locked Tm:YAG ceramic lasers operated at 2012 nm, with over 133 nm demonstrated tuning for continuous-wave operation.

Mode-locked Tm,Ho:KLu(WO(4))(2) laser at 2060 nm using InGaSb-based SESAMs.

Passive mode-locking of a Tm,Ho:KLu(WO(4))(2) laser operating at 2060 nm using different designs of InGaAsSb quantum-well based semiconductor saturable absorber mirrors (SESAMs) is demonstrated. The self-starting mode-locked laser delivers pulse durations between 4 and 8 ps at a repetition rate of 93 MHz with maximum average output power of 155 mW. Mode-locking performance of a Tm,Ho:KLu(WO(4))(2) laser is compared for usage of a SESAM to a single-walled carbon nanotube saturable absorber.

Absorption recovery dynamics in 2 µm GaSb-based SESAMs

The interplay between growth and design parameters of GaSb-based quantum-well semiconductor saturable absorber mirrors (SESAMs) and their corresponding absorption recovery time is investigated. The analysis proves an inherently rapid absorption recovery time of GaSb SESAMs operating at a 2??m wavelength range, which is surprisingly independent of the growth temperature for a large temperature range from 350 to 530??C. Moreover, SESAMs incorporating InxGa1?xAsySb1?y quantum wells exhibit a weak variation of the absorption recovery time with changing indium content and with varying lattice strain. The strongest reduction of the absorption recovery time is observed upon placing the quantum wells in the proximity of the SESAMs top layer, and applying an antireflection coating to enhance the interaction with the optical field. Stable mode-locking of a Tm?:?YAG laser at 2??m is obtained with an antireflection coated sample incorporating a single surface quantum well.

GaSb-Based Semiconductor Disk Laser With 130-nm Tuning Range at 2.5

We demonstrate a GaSb-based semiconductor disk laser emitting 0.6 W of output power at 2.5 μm in a fundamental mode regime (M2 <; 1.6). A gain structure grown by molecular beam epitaxy and assembled with an intracavity diamond heat spreader demonstrates a promising potential for power scaling and broad wavelength tuning. A tuning range of 130 nm with output power up to 310 mW has been achieved which represents the largest spectral coverage reported to date for disk lasers at this wavelength.

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We present a gallium antimonide-based semiconductor saturable absorber mirror (SESAM) operating at 2 μm wavelength region. GaSb-based material system is the preferred choice for fabricating surface-normal devices operating beyond 2 μm because it enables the use of highly reflective semiconductor reflectors and quantum wells for wide wavelength range. For the purpose of generating short laser pules, the SESAM was carefully designed to attain a large modulation depth. The device was utilised successfully to passively Q-switch a 2 μm Tm3+-/Ho3+ -doped fiber laser, demonstrating record-short Q-switch pulses of about 20 ns.

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We review recent results concerning the development of GaSb-based heterostructures for semiconductor disk lasers. We focus on fabrication and design details of gain and semiconductor saturable absorber mirrors used to demonstrate disk lasers exhibiting high output power, broad tunability, and short pulse generation. We demonstrate a 2 μm gain structure with 15 InGaSb quantum wells emitting more than 4 W of output power at 15°C. Almost 1W output power was measured at an elevated temperature of 50°C. A tuning range of more than 150 nm was achieved by employing a gain mirror comprising quantum wells with different widths to provide broadband gain. Ultra-short pulse generation based on synchronous mode-locking and a preliminary demonstration of passively mode-locked semiconductor disk lasers based on GaSb saturable absorber mirrors are also discussed.

Highly nonlinear GaSb-based saturable absorber mirrors

A mode-locked thulium-doped YAG ceramic laser delivering 6.3 ps pulses at 2012 nm is demonstrated. The self-starting oscillator is mode-locked by a near-surface GaInSb quantum-well based SESAM.