Q-switched Cavity Research Articles

Deep ultraviolet laser at 223.8 nm with adjustable repetition rate and narrow pulse width.

We presented the first, to our knowledge, demonstration of an ultraviolet (UV) laser at 223.8 nm by six-harmonic generation of an electro-optic Q-switched cavity dumping 1342 nm Nd:YVO4 laser. It offers high power, constant short pulse duration, and adjustable pulse repetition rate. The pulse duration is independent of the pump power and repetition rate compared to classical Q-switched oscillators. The output efficiency of the UV laser is optimized by adjusting the focusing lens. With the incident pump power of 30 W, an maximum average output power of 249 mW was obtained at 13 kHz. The pulse width maintained 3.4-3.5 ns from 5 to 20 kHz. The maximum pulse energy of 28.1 µJ was obtained at 5 kHz, and the corresponding peak power was up to 8.1 kW.

Numerical simulation of a laser with a Q-switched cavity for production of ultrashort pulses

A theoretical model was developed to calculate lasing modes for giant pulses in solid-state lasers with Q-switched cavities. The lasing process begins with steady-state mode locking. Then, when a control pulse is fed to the cavity electro-optic modulator, the light propagating in the cavity is amplified. When the laser pulse reaches maximum energy, the cavity opens, producing a single ultrashort pulse. Simulations performed using a commercial 50 W Nd:YAG solid-state CW laser diode pump module indicated that, when the driver parameters for the electro-optical modulator are optimized, the cavity switching mode can be used for high-efficiency extraction of almost all the energy (up to 20 mJ) stored in the laser medium in steady-state mode in the form of a single pulse with a duration in the hundreds of picoseconds.

Widely-duration-tunable nanosecond pulse Nd:YVO4 laser based on double Pockels cells

The development of duration-tunable pulse lasers with constant output power is important for scientific research and materials processing. We present a widely-duration-tunable nanosecond (ns) pulse Nd:YVO4 laser based on double Pockels cells (PCs), i.e. inserting an extra PC into a conventional electro-optic Q-switched cavity dumped laser resonator. Under the absorbed pump power of 24.9 W, the pulse duration is adjustable from 31.9 ns to 5.9 ns by changing the amplitude of the high voltage on the inserted PC from 1100 V to 4400 V at the pulse repetition rate of 10 kHz. The corresponding average output power is almost entirely maintained in the range of 3.5–4.1 W. This represents more than three times increase in pulse duration tunable regime and average power compared to previously reported results for duration-tunable ns lasers. The laser beam quality factor was measured to be M2 < 1.18.

Generation of RF Intensity-Modulated Laser Pulses by Dual-Frequency Injection Seeding

In order to obtain high peak power RF intensity-modulated pulses for long-distance applications, a Q-switched Nd:YAG laser is injection seeded by a dual-frequency laser signal. The beat note frequency of the dual-frequency laser signal is adjusted to the frequency spacing of two adjacent longitudinal modes of the Q-switched laser. When the dual-frequency signal is injected into the Q-switched slave resonator, simultaneously two cavity axial modes are tuned to allow the injected wave frequencies within the axial modes selection range, the two selected slave cavity modes will oscillate due to phase-pulling effect. The Interference of the two modes results in intensity modulated pulses. The modulation frequency equals to a free spectral range of the Q-switched cavity, which is 225 MHz in our experiment. Maximum intensity-modulated pulse energy of 7 mJ and pulsewidth of 16 ns are measured. The dependence of locking bandwidth to the injected power is also studied experimentally, it is confirmed that the locking bandwidth increases with respect to the injected power of the seed signal. The high peak power RF intensity-modulated pulsed light source is a promising candidate for long-distance lidar-radar applications.

Pulse width adjustable Q-switched cavity dumped laser by rotating a quarter-wave plate and a Pockels cell.

A pulse width adjustable 1064nm Q-switched cavity dumped Nd:YVO4 laser was realized for the first time, to the best of our knowledge, by rotating an intracavity quarter-wave plate (QWP) and a Pockels cell (PC). The pulse width adjustment range was 4.8-7.8ns with a constant output power of 3.6W, and it reached 4.8-13.5ns for a lower output power of 1.3W. The pulse width was dependent mostly on the rotating angle of the QWP and PC, but independent of the gain and pulse repetition rate.

Cavity enhanced rephased amplified spontaneous emission

Amplified spontaneous emission is usually treated as an incoherent noise process. Recent theoretical and experimental work using rephasing optical pulses has shown that rephased amplified spontaneous emission (RASE) is a potential source of wide bandwidth time-delayed entanglement. Due to poor echo efficiency the plain RASE protocol does not in theory achieve perfect entanglement. Experiments done to date show a very small amount of entanglement at best. Here we show that RASE can, in principle, produce perfect multimode time-delayed two mode squeezing when the active medium is placed inside a Q-switched cavity.

Gain versus tuning issues to Q-switch with Yb3+:LSO and amplify broad-bandwidth pulses

The capability of a thin slab of Yb3+:LSO to be tuned within a Q-switched cavity is demonstrated in a range of laser wavelengths from 1052 to 1065 nm. Using a side-pump architecture, to create a linear gain-stripe in the crystal of which the dimensions can be finely controlled, we generate 50 to 150 ns-wide pulses in the range 1–5 mJ. These experimental data are fitted with the theoretical predictions by means of comprehensive modeling. Our model involves all the relevant parameters for the discussion of energetic, spectral and spatial issues of interest to evaluate the potential of this quasi-three-level material in the field of broadband regenerative amplification. Thanks to pure homogeneous broadening, this finally helps us to size a consistent pump design dedicated to the amplification of broad-bandwidth pulses up to a few milli-joules near 1053–1056 nm, the range of wavelengths involved in ICF.

Q-switched chemical HF laser

A numerical simulation was made of pulse-periodic operation of an ultrasonic chemical HF laser with a Q-switched cavity. This simulation was based on a combination of mathematical models of cw and pulsed chemical lasers. Calculations were made specifically for an experimental HF chemical laser with a combustion chamber. It was found that pulse-periodic operation can ensure a 20–28-fold increase in the output power, compared with cw operation, at the expense of a reduction in the average radiation power by a factor less than 2. The energy per unit mass of the active medium increases with increase in the Q-switching frequency, reaching 60 kJ kg-1 (which is half the value obtainable under cw conditions) at the switching frequency of 250 kHz.

Optimal control of the profile and duration of pulses generated in a Q-switched cavity with a dynamic mirror

It is shown that the formation of pulses with a given profile and duration in a cavity Q-switched, in accordance with a specific law, by dynamic control of the reflection coefficient of the output mirror can have an energy efficiency equal to the maximum efficiency of pulse generation by instantaneous Q-switching. A solution is given of the inverse problem of determination of the optimal law of control of the reflection coefficient of the output mirror of the cavity, which ensures generation of pulses with a given profile and duration. Examples of the optimal laws of this kind are considered.

Influence of the spatial structure of seeding radiation on the generation of giant pulses in a laser with a Q-switched cavity

An experimental investigation was made of the special features of the formation of the spatial structure of giant pulses from narrow-band seeding radiation. This radiation was used successfully not only to reduce the width of the spectral band, but also to form the desired structure of the field of giant pulses. It was established that when the 'on' state of a Q switch was sufficiently long (~1 μs), a change in the ratio of the losses experienced by different transverse oscillation modes resulted in the generation of a second giant pulse. The latter pulse was formed from the wideband noise of the amplified luminescence and it represented a different transverse mode with a higher Q factor than that of the seeding radiation.

14- and 16-μ gasdynamic CO2 lasers

Laser action at 16 μ has been obtained between the (02°0) and (0110) levels as well as between the (10°0) and (0110) levels at 14 μ. A 9- or 10-μ saturating pulse equilibrates the (001) level with either the (02°0) or (10°0) level and creates the transient 14- or 16-μ inversion. Extraction efficiencies of 20% have been achieved on a single pulse. Repetition frequencies of 200 Hz have been achieved using a single Q-switched cavity.