Darren Rand

High-energy, kHz-repetition-rate, ps cryogenic Yb:YAG chirped-pulse amplifier

We demonstrate amplification of picosecond laser pulses to 40?mJ at a 2?kHz pulse repetition frequency (PRF) from a two-stage cryogenic chirped-pulse Yb:YAG amplifier, composed of a regenerative amplifier (RGA) and a two-pass booster amplifier. The RGA produces 8.2mJ of energy at 2kHz PRF and 13.2mJ at 1kHz PRF with excellent energy stability (approximately 0.3% rms) and beam quality (M(2)<1.1). Pulse stretching and compression are achieved by using a chirped fiber Bragg grating and a multilayer dielectric grating pair, respectively. Compressed 15?ps pulses from the RGA are obtained with a throughput efficiency of approximately 80% (approximately 6.5 mJ for 2kHz). The booster amplifier further amplifies the pulses to 40mJ at 2kHz PRF, and approximately 32 mJ, approximately 15 ps pulses are expected after compression. The amplifier chain seeded from a femtosecond Yb-fiber laser enables the optical self-synchronization between signal and pump in optical parametric chirped-pulse amplifier applications.

On the Experimental Characterization of Beat Noise in 2-D Time-Spreading Wavelength-Hopping OCDMA Systems

The results of a preliminary experimental characterization of beat noise for the case of a particular two-dimensional time-spreading wavelength-hopping optical code family are presented. Beat noise is evaluated at a data rate of 2.5 Gb/s with and without time gating. Results indicate that this form of noise introduces significant system power penalties for both cases, with the former approach more robust in this respect

Cryogenic Yb 3+ -doped materials for pulsed solid-state laser applications [Invited]

We review recent progress in pulsed lasers using cryogenically-cooled Yb3+-doped gain media, with an emphasis on high average power. Recent measurements of thermo-optic properties for various host materials at both room and cryogenic temperature are presented, including thermal conductivity, coefficient of thermal expansion and refractive index. Host materials reviewed include Y2O3, Lu2O3, Sc2O3, YLF, YSO, GSAG and YVO4. We report on the performance of several cryogenic Yb lasers operating at 5-kHz pulse repetition frequency (PRF). A Q-switched Yb:YAG laser is shown to operate at 114-W average power, with 16-ns pulse duration. A chirped pulse amplifier achieves 115-W output using a Yb:YAG power amplifier. Output power of 73 W is obtained from a composite Yb:YAG/Yb:GSAG amplifier, with pulses that compress to 1.6 ps. Finally, a high-average-power femtosecond laser based on Yb:YLF is discussed, with results for a 10-W regenerative amplifier at 10-kHZ PRF.

Suppression of beating noise of narrow-linewidth erbium-doped fiber ring lasers by use of a semiconductor optical amplifier

Beating noise in narrow-linewidth erbium-doped fiber ring lasers puts severe limitations on applications of the lasers. We demonstrate the suppression of beating noise in fiber ring lasers by using a semiconductor optical amplifier in the laser cavity, which acts as a high-pass filter. Two different ring structures are presented as examples to demonstrate this beating noise suppression.

100-W

This work describes a cryogenic, electro-optically <i>Q</i>-switched Yb:YAG laser that generates 114-W average TEM₀₀ power with 47% optical-to-optical efficiency. Pulse repetition frequency is 5 kHz, pulse duration is 16 ns full-width at half-maximum, and <i>M</i> ² is less than 1.05.

Q

A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps. The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG.

-switched Cryogenically Cooled Yb:YAG Laser

In this paper, we have shown that optical code division multiplexing (O-CDMA) systems at 10 Gb/s that can support at least 10 simultaneous users with BER<10/sup -9/ can be effectively designed for implementation in real networks. The carrier-hopping prime code is chosen to offer the optimum correlation values and maximum cardinality while providing a satisfactory bit error rate (BER). The encoder design can be advantageous of scalability allowed by increasing the code matrix size and the complementary decoder reduces cardinality limitations.

Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG

A multistage cryogenic chirped pulse amplifier has been developed, utilizing two different Yb-doped gain materials in subsequent amplifier stages. A Yb:GSAG regenerative amplifier followed by a Yb:YAG power amplifier is able to deliver pulses with a broader bandwidth than a system using only one of these two gain media throughout. We demonstrate 90 mJ of pulse energy (113 W of average power) uncompressed and 67 mJ (84 W of average power) compressed at 1.25 kHz pulse repetition frequency, 3.0 ps FWHM Gaussian pulse width, and near-diffraction-limited (M2<1.3) beam quality.

A scalable wavelength-hopping, time-spreading optical-CDMA system

Semiconductor cylinder fibers (SCFs) are novel amplifying waveguide structures in which a semiconducting film is interlaid between conventional core and cladding fiber layers. We investigate the modal properties of SCFs by way of a comprehensive model which takes into account the wavelength-dependent refractive indexes of both the core and cladding glass layers and the semiconductor. Our semiconductor model also includes both thin-film effects and carrier-induced changes in the complex refractive index. We show that annular modes which are highly confined to the semiconductor are supported, and we calculate the corresponding modal effective indexes. Finally, we demonstrate that, depending on the pump-induced carrier concentration, a large gain is possible across a broad spectral region.

Picosecond kilohertz-class cryogenically cooled multistage Yb-doped chirped pulse amplifier

A laser amplifier using two cryogenically cooled materials, Gd₃Sc₂Al₃O₁₂ (GSAG) and YAG, demonstrates tens of millijoule pulse energy at kilohertz repetition rates. The near-diffraction-limited output was compressed to picosecond pulse duration.