Optical encryption using phase modulation generated by thermal lens effect

We present the implementation of an experimental optical encryption configuration in the Fresnel domain using the thermal lens effect to modulate the phase of the illumination beam. We corroborate the basic performance of our cryptosystem by performing the encryption-decryption procedure of a single object. Then, we test the tolerance of the proposed scheme to decrypt decryption with keys registered for different modulations of the illumination beam induced by the phase generated due to thermal lens effect. These different phase modulations are obtained by introducing axial displacements of a sample, where the thermal lens effect is induced by an excitation beam. Considering the phase modulation changes in the illumination due to sample displacements, we propose an undercover procedure to further protect the target information using decoy data. The key associated with the target information is obtained when the probe and excitation beams are focused on the same point of the sample, while the decoy object key is registered when the beams are not focused on the same region of the sample. Finally, we analyzed the resistance of the undercover ciphertext to some of the attacks reported in the literature. All experimental results presented in this work demonstrate the basic capabilities, viability, and versatility of our proposals.

The interferometric measurement of thermal lens effect in a LD pumped Tm-doped bulk laser

Directly measuring thermal focal length is important for designing and optimizing the mode locking oscillator, especially for a 2-μm mode-locking laser. In this paper, we propose a novel interferometric method for measuring the thermal focal length in a 2-μm mode-locking laser. This method could give a precise measurement of the thermal focal length inside a long-folded oscillator in both lasing and non-lasing operation. We also theoretically calculate the thermal focal length based on the temperature distribution inside the laser crystal, which matches well with the experimental result

Thermal Lens Technique as a Potential Optical Tool

The spectroscopic characterization of materials involves the use of various optical tools. Spectrometers, interferometers etc, are some of the examples of optical tools. Thermal lens technique is one of the potential optical tools for the thermal characterization of different materials. The thermal lens effect is a photothermal effect which results when energy from a laser beam is absorbed by a sample, causing heating of the sample along the beam path. In this paper an overview of thermal lensing, its significance as potential optical tool and its applications are discussed. Index Terms: Optical tool, Photothermal spectroscopy, TLS application, Thermal diffusivity

Compact 50 W All-Solid-State Picosecond Laser System at 1 kHz

Compact, stable, high-power and high repetition rate picosecond laser systems are excellent sources for optical parametric chirped pulse amplification systems and laser satellite ranging systems. Compared with the traditional complex high-power amplifier, this article reports a compact high-power picosecond laser system at a repetition rate of 1 kHz based on Nd:YAG bulk crystal. The thermal lens effect limits the regenerative amplifier to directly output higher energy. For this reason, multi-stage traveling-wave amplifiers are usually used to gradually increase the laser pulse energy. So as to achieve a compact structure, a regenerative amplifier that can output higher power at 1 kHz is designed in the laser system. The regenerative amplifier can output the power of 6.5 W at the pump power of 41.5 W; the beam quality of M2 factor was about 1.3. A more flexible thermal depolarization compensation structure is applied in the side-pumped amplifier, which can effectively compensate for thermal lens effect and thermal depolarization at different pump powers. Finally, the laser pulse can achieve an output power higher than 50 W at 1 kHz after passing through an end-pumped traveling-wave amplifier and a side-pumped traveling wave amplifier.