Diffraction-limited Pulses Research Articles

1 kHz single-frequency, injection-seeded Er:YAG laser with an optical feedback

A novel 1 kHz single-frequency, Q-switched Er-doped yttrium aluminum garnet (Er:YAG) laser pumped by a 1470 nm laser diode is demonstrated. The 500 ns, 5.52 mJ single-frequency, diffraction-limited pulses are obtained by using a ‘ramp-fire’ injection-seeding technique and an optical feedback architecture. The full width at half-maximum of the pulse spectrum is measured to be 1.47 MHz by using the heterodyne technique. The beam quality M2 factors are measured to be 1.18 and 1.24 in the x and y directions, respectively.

Raman-shifted wavelength-selectable pulsed fiber laser with high repetition rate and high pulse energy in the visible.

A high-pulse-energy, diffraction-limited, wavelength-selectable, visible source, based on Raman frequency shifting of a frequency-doubled Yb-doped fiber laser, has been studied. The relative length-scaling laws of Raman gain and self-phase modulation push the design towards short fiber lengths with large core size. It is experimentally demonstrated that the Raman clean-up effect in a graded-index multi-mode fiber is not sufficient to obtain diffraction-limited beam quality in the short fiber length. Thus, a large-core photonic crystal fiber is used to maintain diffraction-limited performance and output pulse energies of ~1 μJ, at a 1-MHz repetition rate and 1.3-ns pulse-width are successfully achieved. This step-tunable visible source should find applications in photoacoustic microscopy.

Simulations of a FIR Oscillator with Large Slippage parameter at Jefferson Lab for FIR/UV pump-probe experiments

We previously proposed a dual FEL configuration on the UV Demo FEL at Jefferson Lab that would allow simultaneous lasing at FIR and UV wavelengths [1]. The FIR source would be an FEL oscillator with a short wiggler providing diffraction-limited pulses with pulse energy exceeding 50 microJoules, using the exhaust beam from a UVFEL as the input electron beam. Since the UV FEL requires very short pulses, the input to the FIR FEL is extremely short compared to a slippage length and the usual Slowly Varying Envelope Approximation (SVEA) does not apply. We use a non-SVEA code [2] to simulate this system both with a small energy spread (UV laser off) and with large energy spread (UV laser on).

Photon Source Capabilities of the Jefferson Lab FEL

Jefferson Lab operates a superconducting energy recovered linac which is operated with CW RF and which powers oscillator-based IR and UV Free-Electron Lasers (FELs) with diffraction limited sub-picosecond pulses with >1013 photons per pulse (1.0%BW) at pulse repetition frequencies up to 75 MHz. Useful harmonics extend into the vacuum ultraviolet (VUV). Based on FEL model calculations validated using this facility, we have designed both an oscillator-based VUV-FEL that would produce 6 × 1012 coherent (0.5% BW) 100 eV photons per pulse at multi-MHz repetition rates in the fundamental, and a dual FEL configuration that would allow simultaneous lasing lasing at THz and UV wavelengths. The VUV-FEL would utilize a novel high gain, low Q cavity, while the THz source would be an FEL oscillator with a short wiggler providing diffraction limited pulses with pulse energy exceeding 50 microJoules. The THz source would use the exhaust beam from a UV FEL. Such multiphoton capabilities would provide unique opportunities for out of equilibrium dynamical studies at time-scales down to 50 fs. The fully coherent nature of all these sources results in peak and average brightness values that are many orders of magnitude higher than storage rings.

150-ps pulse Raman generator pumped by a 1-kHz sub-nanosecond passively Q-switched laser system

Raman conversion with a single Ba(NO3)2 crystal (barium nitrate) either in single- and double-pass travelling-wave setups has been investigated. A Master-Oscillator-Power-Amplifier (MOPA) system, based on a passively Q-switched (PQS) laser generating 500-ps pulses and delivering a total energy of 350 μJ at 1 kHz, was used as pump source for the Raman generator. The two-passes setup yielded 116-μJ, 150-ps Fourier- and diffraction-limited pulses at 1198 nm for ≈3× the Raman threshold with no additional Stokes lines, and conversion efficiency of 35%. Such results are interesting not only for direct applications of the wavelength-shifted laser source, but also for further pulse-compression and supercontinuum generation in fibers. Indeed, self-phase modulation up to 0.82 nm has been demonstrated (pulse compression down to 5 ps) as well as 120-nm supercontinuum.

Resonantly diode-pumped continuous-wave and Q-switched Er:YAG laser at 1645 nm

We describe an efficient Er:YAG laser that is resonantly pumped using continuous-wave (CW) laser diodes at 1470 nm. For CW lasing, it emits 6.1 W at 1645 nm with a slope efficiency of 36%, the highest efficiency reported for an Er:YAG laser that is pumped in this manner. In Q-switched operation, the laser produces diffraction-limited pulses with an average power of 2.5 W at 2 kHz PRF. To our knowledge this is the first Q-switched Er:YAG laser resonantly pumped by CW laser diodes.

Optical parametric chirped-pulse amplification source suitable for seeding high-energy systems

A short-pulse source based on optical parametric chirped-pulse amplification (OPCPA) technology has been developed with properties that make it a suitable seed for a high-energy OPCPA system. This source generated a diffraction-limited pulse at 910 nm with a full bandwidth of > 165 nm and a spectrum having a transform-limited pulse duration of less than 15 fs. The technique has potential for generating bandwidths > 200 nm and pulse durations < 10 fs.

11 MW peak-power, 7 W average-power, high-spectral-brightness, diffraction-limited pulses from a photonic crystal fiber amplifier

We report a large-core, Yb-doped photonic crystal fiber amplifier generating diffraction-limited (M2 = 1.04), approximately 0.45 ns, approximately 8 GHz linewidth pulses with energies of 540 microJ, peak power in excess of 1.1 MW, and average power of approximately 7.2 W at a repetition rate of 13.4 kHz. The pulse peak spectral brightness exceeds 10 kW/(sr Hz cm2) and is the highest generated by a fiber source, to our knowledge.

1-mJ energy, 1-MW peak-power, 10-W average-power, spectrally narrow, diffraction-limited pulses from a photonic-crystal fiber amplifier

We report on a diode-pumped master-oscillator/fiber-amplifier (MOFA) system consisting of a passively Q-switched, single-frequency Nd:LSB microchip laser that seeds a dual-stage Yb-doped fiber amplifier. A large-core, single-mode photonic crystal fiber was used for the final amplifier. The MOFA generated 1062nm wavelength, 1-ns long, ~10kHz repetition-rate, diffraction-limited pulses of energy >1mJ, peak power >1MW, average power >10W, and spectral linewidth ~9 GHz.

1 ps, 3 mJ KrF laser pulses generated using stimulated Raman scattering and fast Pockels cell

A new simple picosecond KrF laser source was developed by the saturated amplification of sharp leading-edge pulses generated by fast Pockels cell and stimulated Raman scattering (backward Raman pulse compression and four-wave anti-Stokes generation in methane gas). Short-laser pulses of 1.1 ps and 3.2 mJ with a beam quality closed to that of a diffraction-limited pulse were generated at a repetition rate of 10 Hz. The measured brightness contrast ratio of the main pulse to ASE was more than 1010. A stable and long-life operation has been achieved using a fast Pockels cell.

Generation and Complete Electric-Field Characterization of Intense Ultrashort Tunable Far-Infrared Laser Pulses

Intense rapidly tunable picosecond laser pulses have been generated in the far infrared from 30 to 250 \ensuremath{\mu}m, a range not well covered by other sources. The transform-limited, diffraction-limited pulses have energies of up to 17 \ensuremath{\mu}J, peak powers of more than 1 MW, a length of only 18 optical periods, and focused intensities of 0.1 $\mathrm{GW}/{\mathrm{cm}}^{2}$. Measurements of both the optical field amplitude and the phase have been performed at 150 \ensuremath{\mu}m with a rapid-scanning cross-correlation technique probing the field-induced birefringence in ZnTe with a 10-fs Ti:sapphire laser. The far-infrared laser opens up the exciting possibility of performing nonlinear experiments in a relatively unexplored spectral range.

1.5 Watt passively Q-switched diode-pumped cw Nd:YAG laser

A medium-power all-solid-state diode-pumped cw Nd:YAG laser, passively Q-switched employing Cr 4+:YAG as saturable absorber, has been developed. Optimum coupling operation at the 1064 nm working wavelength resulted in 100 μJ, 36 ns, nearly diffraction limited pulses at 15 kHz repetition frequency, with 1.5 W average power output. We discuss the characterisation of the passive Q-switching elements and the laser operation.

Generation of 15-μm radiation through intracavity solid-state Raman shifting in Ba(NO_3)_2 nonlinear crystals

An intracavity solid-state Ba(NO3)2 Raman shifter produces 1.535–1.556-μm radiation when pumped by a Nd3+:YAG laser operating at 1.318–1.338 μm. Raman beam cleanup and 48% energy conversion efficiency have been observed. Second Stokes lines at 1.82–186 μm were observed in the output at higher pump input energy levels. Diffraction-limited pulses of 0.25 J at 1.535–1.56 μm have been achieved.

An efficient ruby laser pumped, diffraction limited dye laser

A longitudinal pumping configuration is described whereby diffraction limited pulses of 15 nsec duration are obtained from a dye oscillator pumped by a giant-pulse single gaussian mode, ruby laser system. Tunable output pulses of 100 kW peak power and a linewidth of 0.16 Å are obtained with a high degree of reproducibility and a conversion efficiency of 6%.