YAG Oscillator Research Articles

Single mode injection seeded Nd:YAG oscillator with an adjustable pulse length between 20 and 50 ns

Highly stable single axial mode operation is obtained in a pulsed injection seeded oscillator with an adjustable pulse length from 20 ns to more than 50 ns, at a constant output energy. The adjustment principle is described experimentally and analysed theoretically. The peak to peak time jitter added to a slow time drift is of the order of 1 nanosecond for a 20 nanoseconds pulse length.

Induced birefringence in optically isotropic glass by a short pulsed Nd:YAG laser

We have observed laser induced birefringence in optically isotropic glasses as well as in Nd:YAG crystal using polarized pulses of wavelength 1.06 µm and duration 100 ps with an intensity near 109 W cm−2. The laser used in the experiment was a Nd:YAG oscillator–amplifier system. The change in the material induced by the laser was not a permanent change but existed for as long as the laser pulse lasted. We observed conoscopic patterns when the laser was passed through glass or the Nd:YAG crystal. These patterns are typically seen when light is passed through birefringent materials kept between a polarizer and analyser. This observation immediately suggests that the glass or the crystal possesses optical birefringence. This birefringence is demonstrated in fused silica glass, Nd:glass and Nd:YAG crystal. The circular symmetric conoscopic patterns show that the optic axis is formed along the direction of laser propagation. The laser induced birefringence depended on the laser intensity and we characterized the magnitude of this change by measuring the output pulse at the end of the crossed polarizer.

Compact laser-diode-based femtosecond sources

This paper describes the development of compact femtosecond laser systems that are capable of being directly pumped by laser diodes or are based directly on laser diodes. The paper demonstrates the latest results in a highly efficient vibronic based gain medium and a diode-pumped Yb:KYW laser is reported that has a wall plug efficiency >14%. A Cr4+:YAG oscillator is described that generates transform-limited pulses of 81 fs duration at a pulse repetition frequency of >4 GHz. The development of Cr3+:LiSAF lasers that can be operated using power supplies based on batteries is briefly discussed. We also present a summary of work being carried out on the generation of fs-pulses from laser diodes and discuss the important issues in this area. Finally, we outline results obtained on the generation of pulses as short as 550 fs directly from a two-section quantum dot laser without any external pulse compression.

Theoretical and experimental investigations of quasi-continuous wave diode array side-pumped Yb:YAG slab laser

An analytical model of quasi-continuous wave (quasi-CW) diode array side-pumped slab laser for Yb:YAG oscillator in long-pulse free-running has been developed based on the CW model. In this model we first introduce a new parameter, pump pulse width and make the model available for use in the quasi-CW model. We also give an analytical equation of laser delay time to calculate the laser pulse width. A detailed model is also presented for a new structure laser design, taking account of the geometry of Yb:YAG slab. A quasi-CW diode array side-pumped Yb:YAG slab laser is investigated theoretically and experimentally. Experiments yield a quasi-CW output energy up to 20.36 mJ with the laser pulse width of 654.55 μs at 1049 nm when the diode arrays operate at 25 Hz and 1 ms pulse width. The crystal dimensions are 3 mm×8 mm×1 mm and the doping density is 10 at.%. The experimental results are in good agreement with the predictions of the theoretical model.

Characterization of Radiative and Nonradiative Processes in Nd:YAG Lasers by Comparing Direct and Band Pumping

Heat generation and laser performance of Nd:YAG oscillators pumped in two regimes, band pumping at /spl sim/808 nm and "thermally boosted" (TB) pumping at 884.5 nm, are compared. The crystal, pumped with a Ti:sapphire laser, lased with slope efficiencies of 52% and 57% when pumped at 802 and 884.5 nm, respectively. The heat generated during lasing was found to be 27% lower with TB pumping as compared to traditional band pumping. Moreover, the experimental results suggest that the coupling efficiency between the pump band and the upper lasing level (the quantum efficiency) is unity, and about 8% of the upper lasing level population decays via nonradiative channels.

Picosecond laser for performance of efficient nonlinear spectroscopy from 10 to 21 microm.

Laser tunability from 10 to 21 microm is obtained by use of an optical parametric oscillator based on a KTP crystal followed by a difference-frequency stage with a CdSe crystal. An all-solid-state picosecond Nd:YAG oscillator mode locked by a frequency-doubling nonlinear mirror is used for synchronous pumping.

50-mJ, Q-switched, 2.09-microm holmium laser resonantly pumped by a diode-pumped 1.9-microm thulium laser.

We report >50-mJ Q-switched energy output from a 2.09-microm Ho:YAG oscillator, resonantly pumped at 1.9-microm by a diode-pumped Tm:YLF laser. We demonstrate a Q-switched-to-normal-mode extraction efficiency of 100% at an output energy of 30 mJ and over 64% at the 50-mJ output level. Operating at 50 mJ (60 Hz) of output, a pulse width of 14 ns is achieved from the holmium oscillator, which corresponds to approximately 3.6 MW of peak power. At the 50-mJ output level, a beam-propagation factor M2 approximately 1.2 is achieved.

Development of a two-color picosecond optical parametric oscillator, pumped by a Nd:YAG laser mode locked using a nonlinear mirror, for doubly-resonant sum frequency generation spectroscopy

We set up a doubly-resonant sum frequency generation (DR-SFG) spectrometer based on the use of an all-solid-state flash-lamp-pumped Nd:YAG laser that synchronously pumps two parametric oscillators. Pulses as short as 12 ps FWHM are generated by mode locking a Nd:YAG oscillator using a frequency doubling nonlinear mirror combined with a two-photon absorber. The available pump power is shared between a LiNbO 3/AgGaS 2 optical parametric oscillator (OPO), tunable from 3800 to 1100 cm −1 and a BBO OPO tunable from 410 to 2600 nm. Spectral resolution and pulse are 2 and 3 cm −1 in the infrared and visible spectral ranges, respectively. First DR-SFG spectra of self-assembled monolayers on Au are presented.

Increase in phase-conjugate reflectivity of a holographic Nd:YAG oscillator due to resonant refractive-index grating

We have studied both experimentally and numerically the role of resonant refractive-index gratings (RIGs) in a self-pumped phase-conjugate mirror based on an Nd:YAG amplifier with nonreciprocal feedback loop. In experiment the generation of the phase-conjugating laser was delayed with respect to the recording of a holographic nonlinear mirror by an external beam. An increase in the phase-conjugate reflectivity at a delay time of about 3 μs was measured. The numerical calculation confirmed the additional contribution that the resonant RIG formed in a pumped Nd:YAG crystal because of excitation of a higher-lying level of Nd 3+ ions make to the efficiency of phase conjugation.

Spatial mode control of a diode-pumped Nd:YAG laser by use of an intracavity holographic phase plate

We present a new method of realizing phase plates by phase-volume holography on a photopolymer film. We implement such a component in a diode-pumped Nd:YAG oscillator to control the output spatial beam profile. Flattop super-Gaussian and square-shaped beams are obtained.

Nd:YAG oscillator–amplifier system with a passive ring self-pumped phase-conjugate mirror

A ring self-pumped phase-conjugate mirror with rhodium-doped barium titanate is used to correct aberrations in a laser-diode-pumped zigzag slab Nd:YAG oscillator-amplifier system. A diffraction-limited output of 360 mJ is achieved in a 36-ns pulse duration at a repetition rate of 100 Hz.

High-repetition rate 1-J green laser system

A laser-diode-pumped high-repetition-rate zigzag slab Nd:YAG oscillator-amplifier system is developed as the pumping source of a high-average-power and terawatt Ti:sapphire chirped pulse amplification laser system. This system can produce a greater than 2-J high-energy fundamental laser pulse at a repetition rate of 100 Hz. The frequency-doubled energy with a diffusion-bonded KTP crystal is 1 J at a repetition rate of 100 Hz.

The Laser Vegetation Imaging Sensor: a medium-altitude, digitisation-only, airborne laser altimeter for mapping vegetation and topography

The Laser Vegetation Imaging Sensor (LVIS) is an airborne, scanning laser altimeter, designed and developed at NASA's Goddard Space Flight Center (GSFC). LVIS operates at altitudes up to 10 km above ground, and is capable of producing a data swath up to 1000 m wide nominally with 25-m wide footprints. The entire time history of the outgoing and return pulses is digitised, allowing unambiguous determination of range and return pulse structure. Combined with aircraft position and attitude knowledge, this instrument produces topographic maps with dm accuracy and vertical height and structure measurements of vegetation. The laser transmitter is a diode-pumped Nd:YAG oscillator producing 1064 nm, 10 ns, 5 mJ pulses at repetition rates up to 500 Hz. LVIS has recently demonstrated its ability to determine topography (including sub-canopy) and vegetation height and structure on flight missions to various forested regions in the US and Central America. The LVIS system is the airborne simulator for the Vegetation Canopy Lidar (VCL) mission (a NASA Earth remote sensing satellite due for launch in year 2000), providing simulated data sets and a platform for instrument proof-of-concept studies. The topography maps and return waveforms produced by LVIS provide Earth scientists with a unique data set allowing studies of topography, hydrology, and vegetation with unmatched accuracy and coverage.

Output energy fluctuations of the Nd:YAG amplifier chain of a photoinjector drive laser system

In the Etude d'un LaSer Accordable, electron bunches consist of trains of picosecond pulses extracted from a photocathode by a drive laser system: This system consists of a mode-locked Nd:YAG oscillator followed by a pulse compressor, an amplifier chain, and a second-harmonic-generation stage. The performance of the linac critically depends on the energy stability of this system. It is demonstrated theoretically and experimentally that the energy fluctuations of the Nd:YAG oscillator are significantly reduced by the amplifier chain, that the remaining energy fluctuations of the whole system are mainly due to amplifier pump fluctuations, and that the amplifier chain can be optimized to reduce the global energy fluctuations from 1.5% rms to <1% rms.

Diode-pumped high-efficiency high-brightness Q-switched ND:YAG slab laser

A high-efficiency diode-pumped Q-switched Nd:YAG oscillator designed for future spaceborne applications has been demonstrated and characterized. The laser is based on a side-pumped slab geometry and uses an unstable resonator with a radially variable-reflectivity output coupler. The laser provides an output pulse energy of 100 mJ at a 100-Hz repetition rate, with a near-diffraction-limited beam and an overall electrical optical efficiency exceeding 6%.

Diode-pumped grazing incidence slab lasers

Diode-pumped grazing incidence slab (GISL) lasers, and materials which may be used with this configuration, are discussed. Of the materials investigated so far, Nd:YVO/sub 4/ has been shown to yield high efficiency and high small-signal gain, and a compact, 1-kHz repetition rate laser, using a Nd:YVO/sub 4/ slab has generated 3-ns duration, millijoule pulses with high beam quality. A numerical model for GISL lasers has been developed and used to simulate a hybrid Nd:YVO/sub 4//Nd:YAG oscillator. A preliminary, experimental investigation of such a hybrid system has yielded results that are consistent with the model predictions.

Laser drilling of advanced materials: Effects of peak power, pulse format, and wavelength

The quality of laser-drilled holes is significantly influenced by the laser peak power, pulse format, and wavelength. Three advanced materials are used to demonstrate the importance of choosing the correct laser parameters for a specific material. The materials are: (1) intermetallic single crystal nickel aluminide (NiAl) alloy; (2) N5, a single crystal nickel-based superalloy; and (3) a silicon carbide (SiC) ceramic matrix composite (CMC). The laser peak power is varied in terms of the pulse duration and format. For low peak powers, long pulse format (pulse lengths on the order of ms), conventional and also shaped-pulse (burst) commercial rod Nd:YAG laser systems were used. For high peak powers, a short pulse format was adopted for the laser used, namely a cw-pumped Q-switched or modelocked/Q-switched Nd:YAG oscillator followed by a cw-pumped multipass amplifier using a face-pumped, total internal reflection Nd:YAG slab as the gain medium. Finally, a KrF excimer laser operating at a 248 nm wavelength was used. The excimer wavelength was chosen to be close to the Nd:YAG fourth harmonic.

All-solid-state gain-switched Cr 4+:forsterite laser

We developed an all-solid-state Cr 4+:forsterite laser pumped by a kHz Q-switched diode-pumped Nd:YAG oscillator. The laser is tunable from 1190 to 1310 nm, and generates pulses with duration ≈ 70–100 ns and maximum energy ≈ 14 μJ at 1230 nm, corresponding to a pumping efficiency ≈ 10%. This system could be employed as a regenerative amplifier in an ultrafast all-solid-state system based on Cr 4+:forsterite.

Energy optimisation of an Nd:YAG-based four-wave-mixing oscillator with feedback and investigation of its adaptive properties in the pulse-periodic regime

Theoretical and experimental optimisation was made of the parameters of an Nd:YAG oscillator based on four-wave mixing (FWMF) with feedback. Use was made of a thermal-nonlinearity hologram and the energy efficiency under conditions of generation of giant pulses was determined. The efficiency reached was 60% when the energy pulse was 200 mJ for a 2-mm input beam of 50 mJ energy. The ability of the system to operate in the pulse-periodic (up to 25 Hz) conditions was demonstrated.

Pulse-periodic Nd:YAG laser system with compensation of wavefront distortions

A pulse-periodic Nd:YAG oscillator—amplifier system with compensation of wavefront distortions was assembled. The success of the compensation was deduced from the efficiency of second-harmonic generation in a KDP crystal. Right up to the pulse repetition frequency of 50 Hz the system retained near-diffraction divergence of the output radiation.