The results of the development of repetitively pulsed, diode-pumped, electro-optically controlled picosecond Nd:YAG lasers of two designs are presented. The first design uses the active—passive mode locking with electro-optical lasing control and semiconductor saturable absorber mirrors (SESAM). This design allows the generation of 15–50-ps pulses with an energy up to 0.5 mJ and a maximum pulse repetition rate of 100 Hz. The laser of the second design generates 30-ps pulses due to combination of positive and negative electro-optical feedback and the control of the electro-optical modulator by the photocurrent of high-speed semiconductor structures.

https://iopscience.iop.org/article/10.1070/QE2005v035n01ABEH002893/pdf

Pulsed-diode-pumped, all-solid-state, electro-optically controlled picosecond Nd:YAG lasers

Feedback-controlled mode locking (FCM) of Nd:YAG-, YAP-, and YLF-laser oscillators with superior pulse properties is demonstrated. Microsecond trains of ultrashort laser pulses are generated with durations of 11 psec (YAG), 9.8 psec (YAP), and 6.7 psec (YLF), respectively, governed by the fluorescence linewidths. Inserting an antiresonantly tuned etalon in the cavity yields stable operation with even shorter pulses of 6.4, 5.9, and 4.7 psec, respectively, and a reproducibility of ±5%.

Feedback-controlled mode-locking operation of Nd-doped crystal lasers

The development of a stable pulsed yttrium aluminate laser with hybrid mode locking and passive intracavity negative feedback utilizing a GaAs laser is reported. The laser emits bandwidth-limited pulses of 4.5 ± 0.5 ps duration with an energy instability of 1.5%.

Stable picosecond YAlO3:Nd crystal laser with hybrid mode locking and passive intracavity feedback utilizing a GaAs crystal

An electrically controlled feedback loop was used in a phosphate glass laser with passive mode locking to ensure stable generation of 500–600 fs pulses. This negative feedback loop ensured a high reproducibility of the energy and time characteristics of the pulses. The product of the spectral width of the pulses and their duration was 0.44.

Highly stable subpicosecond neodymium (Nd3+) glass laser with passive mode locking and negative feedback

Additive-pulse modelocking of non-cw neodymium lasers

Reproducible generation of steady-state ultrashort pulses (of ~7.4 psec duration) was achieved for the first time in a pulsed ruby laser with passive mode locking. The lasing was stabilized by a slow-response negative feedback established by an electrooptic switch. An experimental study was made of the formation of steady-state ultrashort pulses from initial radiation fluctuations. The proposed method should be suitable for the generation of reproducible pulses of ~100 fsec duration in wide-band amplifying media.

Steady-state ultrashort pulses generated by passive mode locking of a solid-state laser with an active feedback

A superregenerative amplification scheme was used to obtain unidirectional stimulated emission from a ruby ring laser under free-oscillation and Q-switched conditions. The duration of external control pulses was either tc > L/c or tc < L/c. The carrier frequency of giant pulses could be tuned within a range of 0.25 nm when the spectrum was 6×10–5 nm wide. Reproducible generation of short high-coherence light pulses was achieved.

Ruby ring laser subjected to an external signal

An experimental investigation was made of a new method for controlling the duration of ultrashort pulses in the widest possible range (for pulses shorter than the resonator length) from the axial period to the reciprocal of the width of the gain band of the active medium. The method ensured complete reproducibility of all the parameters of the output radiation. A ruby laser with a saturable absorber in the resonator emitted pulses of ~35 psec duration when pulses of ~1.5 nsec duration were injected from outside into the resonator (the reduction in the pulse duration thus exceeded a factor of 40). The width of the emission spectrum was then close to the limit for a pulse with an exponential envelope.

Control of the duration of ultrashort pulses emitted from a Q-switched solid-state laser

A strong (by a factor of almost 100) narrowing of the spectrum was observed in quasi-stady operation of a solid-state laser with neodymium-doped potassium gadolinium tungstate when the cavity contained a negative feedback loop and a slow-response saturable absorber. The role of a nonlinear narrow-band selector, which reduced the width of the spectrum, was played by a periodic saturated-absorption grating formed by a standing intracavity laser radiation wave in a lithium fluoride crystal containing F2- colour centres and used as a saturable absorber.

Narrowing of the emission spectrum of a solid-state laser with a slow-response saturable absorber and negative feedback

Two-beam interferometer with fixed mirrors and fixed recording media, analytical analysis of optical scheme and design of the construction are presented. Tuning of the spatial frequency of the interference pattern on the media is carried out by rotation simulation mechanism. A working sample device of interferometer based on a beam-splitting cube 20 mm in size and implementing the investigated concept has been created. In the device, a half of convergence angle of interfering beams with a diameter of 5 mm is tunable in the range from 11 to 19°, its value is setting using a degree scale with a resolution of 0.1°. The deviation of actual value of the angle through the scale reading is experimentally obtained in the device. It was found that the absolute error does not exceed 1%. Developed interferometer may be useful an instance in holographic (including liquid) materials studies, development a new design of static Fourier spectrometers and making the interference based lithography process. 

V D Ugozhaev

Papers

Steady-state ultrashort pulses generated by passive mode locking of a solid-state laser with an active feedback

Ruby ring laser subjected to an external signal

Control of the duration of ultrashort pulses emitted from a Q-switched solid-state laser

Narrowing of the emission spectrum of a solid-state laser with a slow-response saturable absorber and negative feedback

A two-beam interferometer with the tuning of the interference pattern period by simulating its rotation