About laser crystals – all you need to know

Special features:

– High conversion efficiency;

– Excellent optical properties;

– Lasing modes: continuous, free generation or Q-modulation;

– The lowest generation threshold among standard erbium-doped crystals;

– the highest differential quantum efficiency among standard erbium-doped crystals;

– Natural disorder leading to an increase in the width of the spectral pumping line and in strength;

– Flash lamp (chromium absorption bands) or diode (erbium bands) pumping;

– Long fluorescence lifetime.

Main properties of Er,Cr:YSGG crystals:

A laser diode-pumped Nd:YVO4 crystal was combined with crystals with a high non-linearity factor (LBO, BBO  or KTP) to shift the frequency of the lasing output from the near-IR to the green, blue or even UV spectral region.  This combination in solid-state lasers is an ideal tool for most common laser applications, including material processing, spectroscopy, wafer quality control systems, laser printing, etc. It is proven that diode-pumped ND: YVO4 solid-state lasers quickly gain markets where water-cooled ion lasers and lamp-pumped lasers traditionally dominate, especially when a compact design and emission with a single longitudinal mode are required.

Advantages of Nd:YVO4 lasers over Nd:YAG:

– The absorption coefficient is 5 times greater in the whole wide pumping range around 808 nm (besides, the dependence on the pump wavelength is much lower, and there is also a strong tendency to form single-mode emission);

– The stimulated emission cross-section is 3 times larger at a wavelength of 1064 nm;

– Lower generation threshold and higher differential quantum efficiency;

– Uniaxial crystal with double refraction: linearly polarized radiation.

Special features:

– Doping: 0.1% – 3%;

– Doping material concentration tolerance: ±0.05% (atoms%<1%), ±0.1% (atoms%≥1%);

– Crystals of various sizes and of high quality;

– 10 000 items Nd:YVO4 per month 3x3x0.5 – 4x4x8 mm³ in size;

– Competing prices.

Nd:YVO4 crystal absorption curve ( 0.5% doping, 4 mm thick)

Nd:YVO4 crystal properties

Nd:YVO4 lasers properties 

1. One of the most appealing properties of Nd:YVO4 crystals is their absorption coefficient, which is 5 times bigger than that of Nd:YAG crystals in a wide range with a peak around 808 nm, what corresponds to the standard wavelength of laser diodes of high power. It means that it is possible to use more compact crystals in lasers, resulting in size reduction of a coherent radiation source system as a whole. Besides, lower power of a pumping laser diode is needed, which, in its turn, increases the laser diode lifetime. The absorption bandwidth of Nd:YVO4 may be 2.4 – 6.3 times bigger than that of Nd:YAG crystals. High efficiency of pumping allows choosing less expensive laser diodes for pumping.

2. Nd:YVO4 crystals have a wider cross-section of stimulated emission at both 1064 nm and 1342 nm wavelengths.  At 1064 nm wavelength lasing, this cross-section is 4 times as big as the cross-section of a similar Nd:YAG crystal; at  1340 nm lasing the cross-section is 18 times bigger. This enables Nd:YVO4 lasers to support powerful single-mode radiation at both wavelengths.

3. Unlike Nd:YAG crystals with cubic symmetry, Nd:YVO4 crystals are single uniaxial, which makes it possible to generate linear polarized emission. Though, the service lifetime of Nd:YVO4 is 2.7 times shorter than that of  Nd:YAG, their differential quantum efficiency is rather high due to the high pumping efficiency.

Comparison of Nd:YVO4 and Nd:YAG characteristics is given below:

stimulated emission cross-section (σ), absorption coefficient (α), fluorescence lifetime (τ), absorption length (Lα), threshold power (Pth) and quantum efficiency of pumping (ηs).

Nd:YVO4 and Nd:YAG characteristics

Comparison of Nd:YVO4 and diode-doped Nd:YAG lasers

Diode-pumped Nd:YVO4+KTP laser

– 8 W green light generated by an Nd:YVO4 (0.5% doping, 15 W pumping laser diode. KTP crystal inside the resonator.

– 200 mW green light generated by an Nd:YVO4 (2% doping, 1 W pumping laser diode.

– KTP crystal: 2x2x5 mm³, Nd:YVO4 crystal: 3x3x1 mm³.

Anti-reflective coating

– Both butt-ends with anti-reflective coating for 1064/808 nm, R<0.2% at 1064 nm, R<2% at 808 nm;

– 1 surface: high reflective coefficient coating at 1064&532 nm, with high transmittance coefficient for 808 nm, R>99.8% at 1064&532, T>90% at 808 nm;

– 2 surface: anti-reflective coating at 1064&532 nm, R<0.2% at 1064 nm; R<0.5% at 532 nm;

– 1 surface: high reflective coefficient coating at 1064 nm, with high transmittance coefficient for 808 nm, R>99.8% at 1064, T>95% at 808 nm;

– 2 surface: anti-reflective coating at 1064 nm, R<0.1% at 1064 nm;

– 1, 2 surface: anti-reflective coating, 3 surface: gilding / chrome plating;

– Both butt-ends with anti-reflective coating at 1064 nm, 3 surface anti-reflection coating for 808 nm;

– Other variants of coating at request.

Special features:

– Wide cross-section of stimulated emission at the laser wavelength;

– High absorption coefficient and wide operation range at the pumping wavelength;

– Low pumping wavelength dependency;

– High thermal conductivity;

– Low lasing threshold, high differential quantum efficiency;

– High damage threshold;

– Highly polarized laser radiation;.

Main properties:

– Wavefront distortion: <λ/4 at 633 nm;

– Crystal dimension limit: (W±0.1 mm)x(H±0.1 mm)x(L+0.2/-0.1mm);

– Aperture: >90%;

– Flatness: λ/8 at 633 nm, λ/4 at 633 nm for crystals< 2 mm thick;

– Surface quality 10/5 Scratch/Dig (characteristic chip size) (MIL-PRF-13830B);

– Parallelism: < 20 arcseconds;

– Perpendicularity: ≤5 arcseconds;

– Angle tolerance: ＜±30′.

Nd:GdVO4 crystals characteristics+

Nd:GdVO4 and Nd:YVO4 properties comparison

Comparison of neodymium laser material properties

Nd:YAG crystals advantages:

– High gain coefficient;

– Low lasing threshold;

– High efficiency;

– High optic characteristics;

– Low losses at 1064 nm;

– Good thermal conductivity and thermostability;

– High mechanical toughness;

– Lasing modes: continuous, pulse, Q modulation, mode synchronization.

Special features:

– Size: 15×180 mm² – 40×2 mm²;

– Nd doping: 0.3~2.0(±0.1) % atoms;

– Diameter tolerance: ±0.05 mm;

– Length tolerance: ±0.5 mm;

– Perpendicularity: ≤5 angular minutes;

– Parallelism: <10 angular minutes;

– Wavefront distortion: λ/8;

– Flatness: λ/10;

– Surface quality: 10/5 (MIL-O-13830A);

– Highly reflective coating: R>99.8% at 1064 nm, R< 5% at 808 nm;

– Anti-reflective coating (one layer of MgF₂): R<0.25% for each surface (at 1064 nm);

– Other reflective coatings for 1064/532 nm, 946 nm, 1319 nm, etc.;

– Damage threshold: >500 MW/ cm².

Nd:YAG crystals main features

Nd:YAG crystals optic parameters

Optional Nd:YAG rods and sheets are available for ordering, Nd:YAG rods for 946 nm and 1319 nm. Er:YAG, Yb:YAG and other ion-doped YAG crystals are delivered at request.

Cr ⁴⁺ :YAG crystals with doping in the range of 0.5 mole% – 3 mole% are available for ordering. Crystal sizes vary from 2×2 mm² to 14×14 mm² , from 0.1 mm to 12 mm long. The transmittance coefficient may vary from 10% to 92% according to the request.

Preliminary experiments with Cr 4+: YAG crystals showed that the pulse width of passively Q-switched lasers can be shorter than 5 ns for diode-pumped Nd: YAG lasers, and a pulse repetition rate of 10 kHz for diode-pumped Nd: YV lasers.

Cr ⁴⁺ :YAG crystals can be also used as laser crystals for lasers adjustable in the range of 1.35 – 1.55 um. When   Nd:YAG laser pumped at a wavelength of 1.064 um, this source can generate ultrashort pulses.

Attention: when ordering Cr ⁴⁺ :YAG crystals specify the size, coating type and crystal transmittance coefficient.

Cr ⁴⁺ :YAG crystals properties

Specific features:

– High differential quantum efficiency;

– Lamp or diode pumping;

– Operation at room temperature;

– Operates at the eye-safe wavelength.

Ho:Cr:Tm:YAG crystals technical features

Special features:

– High efficiency;

– Low lasing threshold;

– UV exposure resistance;

– High thermal resistance;

– High quality.

Optic and spectral properties of Nd:Ce:YAG crystals

Characteristic features:

– Heating: less than 11 %;

– High differential quantum efficiency;

– Wide absorption band: 8 nm at 940 nm;

– No absorption from excited state;

– Reliable InGaAs diode pumping at 940 nm (or 970 nm);

– High  thermal conductivity and endurance;

– Excellent optic qualities.

Yb:YAG crystals technical features

Specific features

– High differential quantum efficiency;

– Very good for operation at room temperature;

– Works at a relatively eye-safe spectral wavelength range.

Technical features of Er:YAG crystals

Special features:

– Rod size (diameter), 1 – 150 mm(long);

– Rod axis  orientation  against crystal axis:  around 1;

– Polished  surface or anti-reflective coating;

– Doping elements concentration  (Nd): 0.4 – 1.2 at. %;

– Other doping elements sizes and concentrations are available at request.

 Nd:YLF crystal optical  properties

Nd:YLF crystals physical properties

Refraction index of Nd:YLF crystals

Thermo-optic coefficients of Nd:YLF dn/dT crystals

Sellmeyer’s ratio (λ in um)

n_o²=1.38757+0.70757λ²/(λ²-0.00931)+0.18849λ²/(λ²-50.99741)

n_e²=1.31021+0.84903λ²/(λ²-0.00876)+0.53607λ²/(λ²-134.9566)

Nd:YLF laser crystals specification

Specific features:

– Sizes:  from 2 to 6 mm (rod diameter), 1 – 180 mm (rod length);

– Doping elements concentration (Cr): 0.5~1.0 mole%;

– Parallelism: <10 ″;

– Perpendicularity: <5 ′;

– Angularity: 0.13±0.07 mm ×45°;

– Surface quality: 10/5 (MIL-PRF-13830B);

– Flatness: λ/8 at 632.8 nm;

– Anti-reflective coating: R<0.10% at 850 nm.

Other rod sizes and crystals with non-standard doping elements concentration are available at request.

Cr:LiSAF crystals physical properties

Cr:LiSAF crystal optic properties:

Sellmeyer’s equations (λ in um)

n_c² =1.98448+0.00235/(λ²-0.010936)-0.01057λ²

n_a²=1.97673+0.00309/(λ²-0.00935)-0.00828λ²

Nd:KGW: crystals main properties

Nd:KGW crystals properties:

Nd:KGW crystals specific features

Crystal transmittance curve  Nd:KGW

Yb:KGW crystals main features  

Application:

– Tuneable wavelength in the range of 700 – 1000 nm makes Ti:Sapphire lasers a perfect alternative to dye lasers;

– Ti:Sapphire lasers can be used for UV generation of far UV band (up to 193 nm) with the pulse length up to 10 fs using non-linear crystals (e.g. BBO) to double frequency;

– Ti:Sapphire lasers are also widely used as pumping radiation sources for OPO (optical parametric oscillators) to increase the adjustment range.

Special features:

– Orientation: the optical axis С is perpendicular to the rod axis;

– Concentration of Ti₂O₃: 0.06 – 0.2 mass %;

– Quality index (FOM): 100~250 (>250 at request);

– α₄₉₀: 1.0~4.0 cm^-1;

– Diameter: 2~30 mm or as required;

– Optical path length: 2~30 mm or as required;

– Butt-end configuration: flat or Brewster angled;

– Flatness: <λ/10 at 633 nm;

– Parallelism: 10 angular seconds;

– Surface quality: :<40/20 scratch/dig (MIL-PRF-13830B);

– Wavefront distortion: <λ/4 per inch.

Notes: Anti-reflective coating at request.

Main properties of Ti:sapphire crystals

There are 3 type of diffusion-bonded crystals: YVO₄+Nd:YVO₄+YVO_4, YAG+ Nd:YAG+YAG, Cr:YAG+Nd:YAG

Diffusion-bonded crystals

The following crystals are available to order:

Diffuse-bonded crystals with different structure configuration are supplied by request.