We describe a pulsed blue (485 nm) laser source based on frequency quadrupling a pulsed Tm fiber laser. Up to 1.2 W at 485 nm was generated with an M2 of 1.3. At 10 kHz pulse repetition frequency, the output pulse at 485 nm was 65 ns FWHM resulting in an estimated peak power of 1.8 kW. We anticipate further improvements in power scaling with higher power Tm fiber lasers and improved conversion efficiency to the blue with optimized AR coatings and nonlinear optical crystals.
KEYWORDS: Infrared lasers, Fiber lasers, Optical amplifiers, Nonlinear crystals, High power lasers, Diode pumped solid state lasers, Laser applications, Frequency conversion, Infrared telescopes, Control systems
An air-cooled, light-weight, fiber-based, high power green laser has been prototyped. The system consists of an all-fibercoupled
IR pump laser at 1064 nm and a frequency-conversion module in a compact and flexible configuration. The IR
laser operates in QCW mode, with 10 MHz pulse repetition frequency and 3-5 ns pulse width, to generate sufficient peak
power for frequency doubling in the converter module. The IR laser can produce more than 200 W in a linearlypolarized
diffraction-limited output beam with high spectral brightness for frequency conversion. The converter module
has an input telescope and an oven with a nonlinear crystal to efficiently convert the 1064-nm IR fiber laser output to
532-nm green output. The IR laser and conversion module are connected via a stainless-steel protected delivery fiber for
optical beam delivery and an electrical cable harness for electrical power delivery and system control. The beam quality
of the 532 nm output remains near diffraction-limited, with M2<1.4. Up to 101 W of 532 nm output was demonstrated
and multi-hour runs were characterized at 75 W output. The weights of the IR laser package and doubler are 69 lbs and
14 lbs respectively. An overview of the system and full characterization results will be presented. Such compact, highbrightness
green laser sources are expected to enable various scientific, defense and industrial applications.
A chirped fiber Bragg grating with a dispersion of 1651ps/nm is used to generate temporally stretched,
frequency chirped pulses from a passively mode locked fiber laser that generates pulses of ~1ps (FWHM)
duration at a repetition rate of 20MHz with 3.5mW average power (peak power of 175W). The use of a
chirped fiber Bragg grating enables the generation of temporally stretched pulses with low peak power so
that non-linear effects in the fiber can be avoided. A fiber based interferometeric arrangement is used for
interfering a reference signal with the reflected signal from the target to realize a coherent heterodyne
detection scheme. In the RF domain, the detected heterodyne beat frequency shifts as the target distance is
changed. A round trip target distance of 14km in air is simulated using 9.3km of optical fiber and a
resolution of less than a millimeter is observed.
Ultrashort pulse lasers based on fiber optic architecture will play a dominant role in the spread of these lasers into research and industrial applications. The principle challenge is to generate adequate pulse energy from singlemode or quasi-singlemode amplifiers which have small cross-sectional area. We demonstrate a robust, all-fiber erbium amplifier system that produces >100 μJ per pulse with 701 fs pulsewidth and M2 < 1.3. We will discuss the salient amplifier dynamics that influence the pulse generation, shaping, and propagation phenomena in state-of-the-art erbium fiber lasers. Furthermore, we show data relevant to applications and implementation of ultrashort pulse lasers.
We demonstrate a chirped-pulse amplification system generating 25 μJ compressed pulses at a center wavelength of
1552.5 nm. The seed module and the amplifier chain are all in-fiber (with a few small fiber-pigtailed free-space
components), followed by a free-space diffraction grating pulse compressor. The amplifier chain contains a pre-amplifier
and a booster whose gain fibers are 45/125 μm core/cladding-diameter, core-pumped Er-doped fibers. The pump lasers
for both amplifiers are single-mode 1480 nm Raman lasers capable of up to 8 W output. The seed module generates up
to 2 ns chirped pulses that are amplified and subsequently compressed to <800 fs duration. At a repetition rate of 50 kHz,
the 2 ns pulses from the seed module were amplified to 72 μJ, resulting in 25 μJ after pulse compression. The
corresponding peak power levels after the amplifier chain and compressor were 36 kW and 31 MW, respectively.
Despite the growing number of biomedical and micromachining applications enabled by ultra-short pulse lasers in
laboratory environments, realworld applications remain scarce due to the lack of robust, affordable and flexible laser
sources with meaningful energy and average power specifications. In this presentation, we will describe a laser source
developed at the eye-safe wavelength of 1552.5 nm around a software architecture that enables complete autonomous
control of the system, fast warm-up and flexible operation. Our current desktop ultra-short pulse laser system offers
specifications (1-5 microJ at 500 kHz, 800 fs-3 ps pulse width, variable repetition rate from 1 Hz to 500 kHz) that are
meaningful for many applications ranging from medical to micromachining. We will also present an overview of
applications that benefit from the range of parameters provided by our desktop platform. Finally, we will present a novel
scalable approach for fiber delivery of high peak power pulses using a hollow core Bragg fiber recently developed for
the first time by Raydiance and the Massachusetts Institute of Technology for operation around 1550 nm. We will
demonstrate that this fiber supports single mode operation for core sizes up to 100 micron, low dispersion and low
nonlinearities with acceptable losses. This fiber is a good candidate for flexible delivery of ultra-short laser pulses in
applications such as minimally accessible surgery or remote detection.
Modelocked semiconductor diode lasers are used as compact sources for multiwavelength generation. The generation of multiple wavelengths can be grouped into 2 general categories: 1) multiple continuous wave, phase locked optical frequencies, or 2) multiple, synchronized modelocked wavelength channels. Applications of these sources are demonstrated in areas of optical sampling, access networks, and arbitrary waveform generation.
Low-capacitance, two-section, curved-waveguide gain elements were packaged with lensed polarization-maintaining fiber within standard-sized butterfly-style packages and shown to produce low-jitter pulses when used within a harmonically modelocked sigma cavity laser (jitter = 25 fs; 10 Hz - 10 MHz). Incorporation of a high finesse etalon filter into the sigma-cavity loop resulted in greater than 25 dB suppression of the supermode spurs while maintaining low integrated phase noise (jitter = 30 fs; 10 Hz - 10 MHz). A module containing the in-line sigma-cavity modelocked laser source and packaged semiconductor optical amplifiers was developed to create a configurable low jitter pulse source.
We report optical frequency comb drift stabilization of an external cavity semiconductor laser hybridly modelocked at the 10 GHz cavity fundamental using the Pound-Drever-Hall frequency stabilization scheme. Laser longitudinal mode comb was locked to a Fabry-Perot reference cavity with a finesse value of 214. The frequency error signal was fed back to the bias current of the semiconductor gain medium to change the effective laser cavity length through the coupling between carrier density and refractive index. The peak-to-peak 2.4 GHz frequency drift of the comb of longitudinal modes was reduced to a RMS fluctuation of 30 MHz for up to 5 minutes. To the authors’ knowledge, this is the first optical frequency comb stabilization of a modelocked semiconductor laser. The intended application of the optical frequency stabilization is to keep the laser optical frequency comb locked to a WDM filter that is used for spatially separating the individual longitudinal modes of the laser for photonic arbitrary waveform generation.
We report the measurement of electric field correlations of a hybridly modelocked external linear cavity semiconductor laser as a function pulse delay. We also report the measurement of residual phase noise corner frequency and longitudinal mode linewidth as a function of laser cavity length. We find that the pulses in the modelocked pulsetrain are correlated at only multiples of the cavity roundtrip time. Excellent agreement between residual phase noise corner frequency and longitudinal mode linewidth measurements suggest that the corner frequency is the average longitudinal mode linewidth. This relationship leads to a fundamental limit in the timing jitter of modelocked lasers.
A novel approach to residual jitter measurement examines the intensity cross correlation generated by two optical pulses with various relative delays. A relative delay of 25 pulses produces a residual jitter value of 26 fsec RMS for a 10 GHZ actively mode-locked ring laser. The phase noise measurement carried out to the Nyquist frequency offset gives 47 fsec RMS pulse-to-pulse timing jitter. The field correlation measurement obtains a 10 asec RMS pulse-to-pulse optical carrier jitter.
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